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KSH(1)                               General Commands Manual                               KSH(1)

NAME
       ksh, rksh - KornShell, a standard/restricted command and programming language

SYNOPSIS
       ksh [ +-abcefhiklmnprstuvxBCDEGH ] [ +-o option ] ... [ - ] [ arg ... ]
       rksh [ +-abcefhiklmnpstuvxBCDEGH ] [ +-o option ] ... [ - ] [ arg ... ]

DESCRIPTION
       Ksh is a command and programming language that executes commands read from a terminal or a
       file.  Rksh is a restricted version of the command interpreter ksh; it is used to  set  up
       login  names  and execution environments whose capabilities are more controlled than those
       of the standard shell.  See Invocation below for the meaning of arguments to the shell.

   Definitions.
       A metacharacter is one of the following characters:

              ;   &   (   )   |   <   >   new-line   space   tab

       A blank is a tab or a space.  An identifier is a sequence of letters,  digits,  or  under-
       scores  starting with a letter or underscore.  Identifiers are used as components of vari-
       able names.  A vname is a sequence of one or more identifiers separated by a . and option-
       ally  preceded  by  a ..  Vnames are used as function and variable names.  A word is a se-
       quence of characters from the character set defined by the current locale, excluding  non-
       quoted metacharacters.

       A  command  is  a  sequence  of characters in the syntax of the shell language.  The shell
       reads each command and carries out the desired action either directly or by invoking sepa-
       rate  utilities.   A built-in command is a command that is carried out by the shell itself
       without creating a separate process.  Some commands are built-in  purely  for  convenience
       and  are  not documented here.  Built-ins that cause side effects in the shell environment
       and built-ins that are found before performing a path search  (see  Execution  below)  are
       documented  here.  For historical reasons, some of these built-ins behave differently than
       other built-ins and are called special built-ins.

   Commands.
       A simple-command is a list of variable assignments (see Variable Assignments below)  or  a
       sequence  of blank separated words which may be preceded by a list of variable assignments
       (see Environment below).  The first word specifies the name of the command to be executed.
       Except as specified below, the remaining words are passed as arguments to the invoked com-
       mand.  The command name is passed as argument 0 (see exec(2)).  The value of a simple-com-
       mand  is its exit status; 0-255 if it terminates normally; 256+signum if it terminates ab-
       normally (the name of the signal corresponding to the exit status can be obtained via  the
       -l option of the kill built-in utility).

       A  pipeline  is a sequence of one or more commands separated by |.  The standard output of
       each command but the last is connected by a pipe(2) to the standard input of the next com-
       mand.   Each  command,  except  possibly the last, is run as a separate process; the shell
       waits for the last command to terminate.  The exit status of a pipeline is the exit status
       of  the last command unless the pipefail option is enabled.  Each pipeline can be preceded
       by the reserved word !  which causes the exit status of the pipeline to become  0  if  the
       exit  status of the last command is non-zero, and 1 if the exit status of the last command
       is 0.

       A list is a sequence of one or more pipelines separated by ;, &, |&, &&, or  ||,  and  op-
       tionally terminated by ;, &, or |&.  Of these five symbols, ;, &, and |& have equal prece-
       dence, which is lower than that of && and ||.  The symbols  &&  and  ||  also  have  equal
       precedence.  A semicolon (;) causes sequential execution of the preceding pipeline; an am-
       persand (&) causes asynchronous execution of the preceding pipeline (i.e., the shell  does
       not wait for that pipeline to finish).  The symbol |& causes asynchronous execution of the
       preceding pipeline with a two-way pipe established to the parent shell; the standard input
       and  output of the spawned pipeline can be written to and read from by the parent shell by
       applying the redirection operators <& and >& with arg p to commands and by using -p option
       of  the  built-in  commands read and print described later.  The symbol && (||) causes the
       list following it to be executed only if the preceding pipeline returns a zero  (non-zero)
       value.   One  or  more new-lines may appear in a list instead of a semicolon, to delimit a
       command.  The first item  of the first pipeline of a list that is a simple command not be-
       ginning  with  a  redirection, and not occurring within a while, until, or if list, can be
       preceded by a semicolon.  This semicolon is ignored unless the showme option is enabled as
       described with the set built-in below.

       A  command  is  either a simple-command or one of the following.  Unless otherwise stated,
       the value returned by a command is that of the last simple-command executed  in  the  com-
       mand.

       for vname [ in word ... ] ;do list ;done
              Each  time  a for command is executed, vname is set to the next word taken from the
              in word list.  If in word ...  is omitted, then the for  command  executes  the  do
              list  once for each positional parameter that is set starting from 1 (see Parameter
              Expansion below).  Execution ends when there are no more words in the list.

       for (( [expr1] ; [expr2] ; [expr3] )) ;do list ;done
              The arithmetic expression expr1 is evaluated first (see Arithmetic  Evaluation  be-
              low).   The  arithmetic expression expr2 is repeatedly evaluated until it evaluates
              to zero and when non-zero, list is executed and  the  arithmetic  expression  expr3
              evaluated.  If any expression is omitted, then it behaves as if it evaluated to 1.

       select vname [ in word ... ] ;do list ;done
              A  select  command  prints  on standard error (file descriptor 2) the set of words,
              each preceded by a number.  If in word ...  is omitted, then the positional parame-
              ters  starting  from  1  are used instead (see Parameter Expansion below).  The PS3
              prompt is printed and a line is read from the standard input.  If  this  line  con-
              sists  of  the  number  of  one of the listed words, then the value of the variable
              vname is set to the word corresponding to this number.  If this line is empty,  the
              selection  list is printed again.  Otherwise the value of the variable vname is set
              to null.  The contents of the line read from standard input is saved in  the  vari-
              able  REPLY.   The list is executed for each selection until a break or end-of-file
              is encountered.  If the REPLY variable is set to null by  the  execution  of  list,
              then  the  selection  list is printed before displaying the PS3 prompt for the next
              selection.

       case word in [ [(]pattern [ | pattern ] ... ) list ;; ] ... esac
              A case command executes the list associated with the  first  pattern  that  matches
              word.   The  form  of  the patterns is the same as that used for pathname expansion
              (see Pathname Expansion below).  The ;; operator causes execution of case to termi-
              nate.  If ;& is used in place of ;; the next subsequent list, if any,  is executed.

       if list ;then list [ ;elif list ;then list ] ... [ ;else list ] ;fi
              The  list  following if is executed and, if it returns a zero exit status, the list
              following the first then is executed.  Otherwise, the list following elif  is  exe-
              cuted  and,  if  its  value  is zero, the list following the next then is executed.
              Failing each successive elif list, the else list is executed.  If the if  list  has
              non-zero  exit status and there is no else list, then the if command returns a zero
              exit status.

       while list ;do list ;done
       until list ;do list ;done
              A while command repeatedly executes the while list and, if the exit status  of  the
              last  command  in the list is zero, executes the do list; otherwise the loop termi-
              nates.  If no commands in the do list are executed, then the while command  returns
              a zero exit status; until may be used in place of while to negate the loop termina-
              tion test.

       ((expression))
              The expression is evaluated using the rules for arithmetic evaluation described be-
              low.   If the value of the arithmetic expression is non-zero, the exit status is 0,
              otherwise the exit status is 1.

       (list)
              Execute list in a separate environment.  Note, that if two adjacent open  parenthe-
              ses  are  needed  for  nesting,  a space must be inserted to avoid evaluation as an
              arithmetic command as described above.

       { list;}
              list is simply executed.  Note that unlike the metacharacters ( and ), { and }  are
              reserved  words  and must occur at the beginning of a line or after a ; in order to
              be recognized.

       [[ expression ]]
              Evaluates expression and returns a zero exit status when expression is  true.   See
              Conditional Expressions below, for a description of expression.

       function varname { list ;}
       varname () { list ;}
              Define  a  function  which is referenced by varname.  A function whose varname con-
              tains a .  is called a discipline function and the portion of the varname preceding
              the  last  .   must refer to an existing variable.  The body of the function is the
              list of commands between { and }.  A function defined  with  the  function  varname
              syntax  can  also  be used as an argument to the .  special built-in command to get
              the equivalent behavior as if the varname() syntax were used to  define  it.   (See
              Functions below.)

       namespace identifier { list ;}
              Defines  or  uses  the  name space identifier and runs the commands in list in this
              name space.  (See Name Spaces below.)

       & [ name [ arg... ]  ]
              Causes subsequent list commands terminated by & to be placed in the background  job
              pool name.  If name is omitted a default unnamed pool is used.  Commands in a named
              background pool may be executed remotely.

       time [ pipeline ]
              If pipeline is omitted the user and system time for the current shell and completed
              child  processes is printed on standard error.  Otherwise, pipeline is executed and
              the elapsed time as well as the user and system time are printed on standard error.
              The TIMEFORMAT variable may be set to a format string that specifies how the timing
              information should be displayed.  See Shell Variables below for  a  description  of
              the TIMEFORMAT variable.

       The  following reserved words are recognized as reserved only when they are the first word
       of a command and are not quoted:

       if then else elif fi case esac for while until do done { } function select time [[ ]] !

   Variable Assignments.
       One or more variable assignments can start a simple command or can  be  arguments  to  the
       typeset,  enum, export, or readonly special built-in commands as well as to other declara-
       tion commands created as types.  The syntax for an assignment is of the form:

       varname=word
       varname[word]=word
              No space is permitted between varname and the = or between = and word.

       varname=(assign_list)
              No space is permitted between varname and the =.  The variable varname is unset be-
              fore the assignment.  An assign_list can be one of the following:
                      word ...
                             Indexed array assignment.
                      [word]=word ...
                             Associative  array  assignment.  If preceded by typeset -a this will
                             create an indexed array instead.
                      assignment ...
                             Compound variable assignment.  This creates a compound variable var-
                             name  with  subvariables of the form varname.name, where name is the
                             name portion of assignment.  The value of varname will  contain  all
                             the  assignment  elements.   Additional assignments made to subvari-
                             ables of varname will also be displayed as part of the value of var-
                             name.   If  no assignments are specified, varname will be a compound
                             variable allowing subsequence child elements to be defined.
                      typeset [options] assignment ...
                             Nested variable assignment.  Multiple assignments can  be  specified
                             by  separating  each  of them with a ;.  The previous value is unset
                             before the assignment.  Other declaration commands such as readonly,
                             enum,  and  other declaration commands can be used in place of type-
                             set.
                      . filename
                             Include the assignment commands contained in filename.

       In addition, a += can be used in place of the = to signify adding to or appending  to  the
       previous  value.  When += is applied to an arithmetic type, word is evaluated as an arith-
       metic expression and added to the current value.  When applied to a string  variable,  the
       value  defined  by  word is appended to the value.  For compound assignments, the previous
       value is not unset and the new values are appended to the current ones provided  that  the
       types are compatible.

       The  right hand side of a variable assignment undergoes all the expansion listed below ex-
       cept word splitting, brace expansion, and pathname expansion.  When the left hand side  is
       an  assignment  is  a compound variable and the right hand is the name of a compound vari-
       able, the compound variable on the right will be copied or appended to the compound  vari-
       able on the left.

   Comments.
       A word beginning with # causes that word and all the following characters up to a new-line
       to be ignored.

   Aliasing.
       The first word of each command is replaced by the text of an alias if an  alias  for  this
       word  has  been  defined.   An  alias  name consists of any number of characters excluding
       metacharacters, quoting characters, file expansion  characters,  parameter  expansion  and
       command  substitution characters, the characters / and =.  The replacement string can con-
       tain any valid shell script including the metacharacters listed above.  The first word  of
       each  command  in  the  replaced text, other than any that are in the process of being re-
       placed, will be tested for aliases.  If the last character of the alias value is  a  blank
       then  the  word  following the alias will also be checked for alias substitution.  Aliases
       can be used to redefine built-in commands but cannot be  used  to  redefine  the  reserved
       words  listed  above.  Aliases can be created and listed with the alias command and can be
       removed with the unalias command.

       Aliasing is performed when scripts are read, not while they are executed.  Therefore,  for
       an  alias  to take effect, the alias definition command has to be executed before the com-
       mand which references the alias is read.

       The following aliases are automatically preset when the shell is invoked as an interactive
       shell, unless invoked in POSIX compliance mode (see Invocation below).  Preset aliases can
       be unset or redefined.
                           history='hist -l'
                           r='hist -s'

   Tilde Expansion.
       After alias substitution is performed, each word is checked to see if it  begins  with  an
       unquoted ~.  For tilde expansion, word also refers to the word portion of parameter expan-
       sion (see Parameter Expansion below).  If a word is  preceded  by  a  tilde,  then  it  is
       checked  up  to  a / to see if it matches a user name in the password database (see getpw-
       name(3)).  If a match is found, the ~ and the matched login name are replaced by the login
       directory of the matched user.  If no match is found, the original text is left unchanged.
       A ~ by itself, or in front of a /, is replaced by $HOME, unless the HOME variable  is  un-
       set, in which case the current user's home directory as configured in the operating system
       is used.  A ~ followed by a + or - is replaced by $PWD or $OLDPWD respectively.

       In addition, when expanding a variable assignment (see Variable Assignments above),  tilde
       expansion  is attempted when the value of the assignment begins with a ~, and when a ~ ap-
       pears after a :.  A : also terminates a user name following a ~.

       The tilde expansion mechanism may be extended or modified by defining one  of  the  disci-
       pline functions .sh.tilde.set or .sh.tilde.get (see Functions and Discipline Functions be-
       low).  If either exists, then upon encountering a tilde word to expand, that  function  is
       called  with  the tilde word assigned to either .sh.value (for the .sh.tilde.set function)
       or .sh.tilde (for the .sh.tilde.get function).  Performing tilde expansion within a disci-
       pline  function  will  not recursively call that function, but default tilde expansion re-
       mains active, so literal tildes should still be quoted where  required.   Either  function
       may  assign  a  replacement  string to .sh.value.  If this value is non-empty and does not
       start with a ~, it replaces the default tilde  expansion  when  the  function  terminates.
       Otherwise, the tilde expansion is left unchanged.

   Command Substitution.
       The  standard output from a command list enclosed in parentheses preceded by a dollar sign
       ( $(list) ), or in a brace group preceded by a dollar sign ( ${ list;} ), or in a pair  of
       grave  accents  (``) may be used as part or all of a word; trailing new-lines are removed.
       In the second case, the { and } are treated as a reserved words so that { must be followed
       by  a  blank  and  } must appear at the beginning of the line or follow a ;.  In the third
       (obsolete) form, the string between the quotes is processed for special quoting characters
       before  the command is executed (see Quoting below).  The command substitution $(cat file)
       can be replaced by the equivalent but faster $(<file).  The  command  substitution  $(n<#)
       will expand to the current byte offset for file descriptor n.  Except for the second form,
       the command list is run in a subshell so that no side effects are possible.  For the  sec-
       ond form, the final } will be recognized as a reserved word after any token.

   Arithmetic Expansion.
       An  arithmetic expression enclosed in double parentheses preceded by a dollar sign ( $(())
       ) is replaced by the value of the arithmetic expression within the double parentheses.

   Process Substitution.
       Each command argument of the form <(list) or >(list) will run process list  asynchronously
       connected to some file in /dev/fd if this directory exists, or else a fifo a temporary di-
       rectory.  The name of this file will become the argument to the command.  If the form with
       >  is  selected then writing on this file will provide input for list.  If < is used, then
       the file passed as an argument will contain the output of the list process.  For example,

              paste <(cut -f1 file1) <(cut -f3 file2) | tee >(process1) >(process2)

       cuts fields 1 and 3 from the files file1 and file2 respectively, pastes  the  results  to-
       gether,  and  sends  it to the processes process1 and process2, as well as putting it onto
       the standard output.  Note that the file, which is passed as an argument to  the  command,
       is a UNIX pipe(2) so programs that expect to lseek(2) on the file will not work.

       Process  substitution of the form <(list) can also be used with the < redirection operator
       which causes the output of list to be standard input or the input for  whatever  file  de-
       scriptor is specified.

   Parameter Expansion.
       A  parameter is a variable, one or more digits, or any of the characters *, @, #, ?, -, $,
       and !.  A variable is denoted by a vname.  To create a variable whose vname contains a  .,
       a  variable  whose  vname  consists of everything before the last . must already exist.  A
       variable has a value and zero or more attributes.  Variables can be  assigned  values  and
       attributes by using the typeset special built-in command.  The attributes supported by the
       shell are described later with the typeset special built-in command.   Exported  variables
       pass  their  attributes  to the environment so that a newly invoked ksh that is a child or
       exec'd process of the current shell will automatically import them, unless the posix shell
       option is on.

       The  shell  supports both indexed and associative arrays.  An element of an array variable
       is referenced by a subscript.  A subscript for an indexed array is denoted  by  an  arith-
       metic  expression (see Arithmetic Evaluation below) between a [ and a ].  To assign values
       to an indexed array, use vname=(value ...) or set -A vname  value ... .  The value of  all
       non-negative subscripts must be in the range of 0 through 4,194,303.  A negative subscript
       is treated as an offset from the maximum current index +1 so that -1 refers  to  the  last
       element.   Indexed  arrays  can be declared with the -a option to typeset.  Indexed arrays
       need not be declared.  Any reference to a variable with a valid subscript is legal and  an
       array will be created if necessary.

       An  associative  array is created with the -A option to typeset.  A subscript for an asso-
       ciative array is denoted by a string enclosed between [ and ].

       Referencing any array without a subscript is equivalent to referencing the array with sub-
       script 0.

       The value of a variable may be assigned by writing:

              vname=value [ vname=value ] ...

       or
              vname[subscript]=value [ vname[subscript]=value ] ...
       Note that no space is allowed before or after the =.
       Attributes  assigned  by the typeset special built-in command apply to all elements of the
       array.  An array element can be a simple variable, a compound variable or an  array  vari-
       able.  An element of an indexed array can be either an indexed array or an associative ar-
       ray.  An element of an associative array can also be either.  To refer to an array element
       that  is part of an array element, concatenate the subscript in brackets.  For example, to
       refer to the foobar element of an associative array that is defined as the  third  element
       of the indexed array, use ${vname[3][foobar]}
       A  nameref  is  a  variable that is a reference to another variable.  A nameref is created
       with the -n attribute of typeset.  The value of the variable at the time  of  the  typeset
       command  becomes  the  variable  that  will be referenced whenever the nameref variable is
       used.  The name of a nameref cannot contain a ..  When a variable or  function  name  con-
       tains  a  .,  and the portion of the name up to the first . matches the name of a nameref,
       the variable referred to is obtained by replacing the nameref portion with the name of the
       variable  referenced  by  the nameref.  If a nameref is used as the index of a for loop, a
       name reference is established for each item in the list.  A nameref provides a  convenient
       way  to  refer  to the variable inside a function whose name is passed as an argument to a
       function.  For example, if the name of a variable is passed as the  first  argument  to  a
       function, the command
              typeset -n var=$1
       inside  the function causes references and assignments to var to be references and assign-
       ments to the variable whose name has been passed to the function.
       If any of the floating point attributes, -E, -F, or -X, or the integer attribute,  -i,  is
       set for vname, then the value is subject to arithmetic evaluation as described below.
       Positional parameters, parameters denoted by a number, may be assigned values with the set
       special built-in command.  Parameter $0 is set from argument zero when the  shell  is  in-
       voked.
       The character $ is used to introduce substitutable parameters.
       ${parameter}
              The  shell  reads  all the characters from ${ to the matching } as part of the same
              word even if it contains braces or metacharacters.  The value, if any, of  the  pa-
              rameter  is  substituted.   The braces are required when parameter is followed by a
              letter, digit, or underscore that is not to be interpreted as  part  of  its  name,
              when  the variable name contains a ..  The braces are also required when a variable
              is subscripted unless it is part of an Arithmetic Expression or a  Conditional  Ex-
              pression.  If parameter is one or more digits then it is a positional parameter.  A
              positional parameter of more than one digit must be enclosed in braces.  If parame-
              ter  is  *  or @, then all the positional parameters, starting with $1, are substi-
              tuted (separated by a field separator character).  If an array vname with last sub-
              script  *  @,  or  for indexed arrays of the form sub1 ..  sub2.  is used, then the
              value for each of the elements between sub1 and sub2 inclusive (or all elements for
              * and @) is substituted, separated by the first character of the value of IFS.
       ${#parameter}
              If parameter is * or @, the number of positional parameters is substituted.  Other-
              wise, the length of the value of the parameter is substituted.
       ${#vname[*]}
       ${#vname[@]}
              The number of elements in the array vname is substituted.

       ${@vname}
              Expands to the type name (See Type Variables  below) or attributes of the  variable
              referred to by vname.
       ${!vname}
              Expands  to  the name of the variable referred to by vname.  This will be vname ex-
              cept when vname is a name reference.
       ${!vname[subscript]}
              Expands to name of the subscript unless subscript is *, @.  or of the form sub1  ..
              sub2.   When  subscript  is *, the list of array subscripts for vname is generated.
              For a variable that is not an array, the value is 0 if the variable is set.  Other-
              wise it is null.  When subscript is @, same as above, except that when used in dou-
              ble quotes, each array subscript yields a separate argument.  When subscript is  of
              the  form  sub1 ..  sub2 it expands to the list of subscripts between sub1 and sub2
              inclusive using the same quoting rules as @.
       ${!prefix@}
       ${!prefix*}
              These both expand to the names of the variables whose names begin with prefix.  The
              expansions otherwise work like $@ and $*, respectively (see under Quoting below).
       ${parameter:-word}
              If parameter is set and is non-null then substitute its value; otherwise substitute
              word.
       ${parameter:=word}
              If parameter is not set or is null then set it to word; the value of the  parameter
              is then substituted.  Positional parameters may not be assigned to in this way.
       ${parameter:?word}
              If  parameter  is  set  and is non-null then substitute its value; otherwise, print
              word and exit from the shell (if not interactive).  If word is omitted then a stan-
              dard message is printed.
       ${parameter:+word}
              If  parameter  is  set  and  is non-null then substitute word; otherwise substitute
              nothing.
       In the above, word is not evaluated unless it is to be used as the substituted string,  so
       that, in the following example, pwd is executed only if d is not set or is null:
              print ${d:-$(pwd)}
       If  the  colon  (  :  )  is omitted from the above expressions, then the shell only checks
       whether parameter is set or not.
       ${parameter:offset:length}
       ${parameter:offset}
              Expands to the portion of the value of parameter starting at the character  (count-
              ing from 0) determined by expanding offset as an arithmetic expression and consist-
              ing of the number of characters determined by the arithmetic expression defined  by
              length.   In  the  second  form, the remainder of the value is used.  If A negative
              offset counts backwards from the end of parameter.  Note that one or more blanks is
              required in front of a minus sign to prevent the shell from interpreting the opera-
              tor as :-.  If parameter is * or @, or is an array name indexed by  *  or  @,  then
              offset  and length refer to the array index and number of elements respectively.  A
              negative offset is taken relative to one greater than the highest subscript for in-
              dexed arrays.  The order for associative arrays is unspecified.
       ${parameter#pattern}
       ${parameter##pattern}
              If  the  shell  pattern  matches  the beginning of the value of parameter, then the
              value of this expansion is the value of the  parameter  with  the  matched  portion
              deleted;  otherwise  the value of this parameter is substituted.  In the first form
              the smallest matching pattern is deleted and in the second form the largest  match-
              ing  pattern  is  deleted.   When parameter is @, *, or an array variable with sub-
              script @ or *, the substring operation is applied to each element in turn.

       ${parameter%pattern}
       ${parameter%%pattern}
              If the shell pattern matches the end of the value of parameter, then the  value  of
              this  expansion is the value of the parameter with the matched part deleted; other-
              wise substitute the value of parameter.  In the first form  the  smallest  matching
              pattern  is deleted and in the second form the largest matching pattern is deleted.
              When parameter is @, *, or an array variable with subscript @ or *,  the  substring
              operation is applied to each element in turn.

       ${parameter/pattern/string}
       ${parameter//pattern/string}
       ${parameter/#pattern/string}
       ${parameter/%pattern/string}
              Expands  parameter and replaces the longest match of pattern with the given string.
              Each occurrence of \n in string is  replaced  by  the  portion  of  parameter  that
              matches  the n-th subpattern.  In the first form, only the first occurrence of pat-
              tern is replaced.  In the second form, each match for pattern is  replaced  by  the
              given  string.   The third form restricts the pattern match to the beginning of the
              string while the fourth form restricts the pattern match to the end of the  string.
              When  string  is null, the pattern will be deleted and the / in front of string may
              be omitted.  When parameter is @, *, or an array variable with subscript  @  or  *,
              the  substitution  operation is applied to each element in turn.  In this case, the
              string portion of word will be re-evaluated for each element.

   Shell Variables.
       The following parameters are automatically set by the shell:
              #      The number of positional parameters in decimal.
              -      Options supplied to the shell on invocation or by the set command.
              ?      The exit status returned by the last executed command. Its  meaning  depends
                     on  the  command or function that defines it, but there are conventions that
                     other commands often depend on: zero typically means  'success'  or  'true',
                     one  typically  means 'non-success' or 'false', and a value greater than one
                     typically indicates some kind of error. Only the 8 least significant bits of
                     $?  (values  0  to 255) are preserved when the exit status is passed on to a
                     parent process, but within the same (sub)shell environment, it is  a  signed
                     integer  value with a range of possible values as shown by the commands get-
                     conf INT_MIN and getconf INT_MAX. Shell functions that run  in  the  current
                     environment may return status values in this range.
              $      The  process  ID  of  the  main shell process. Note that this value will not
                     change in a subshell, even if the subshell runs in a different process.  See
                     also .sh.pid.
              _      Initially, the value of _ is an absolute pathname of the shell or script be-
                     ing executed as passed in the environment.  Subsequently it is assigned  the
                     last  argument  of the previous command.  This parameter is not set for com-
                     mands which are asynchronous.  This parameter is also used to hold the  name
                     of the matching MAIL file when checking for mail.  While defining a compound
                     variable or a type, _ is initialized as a reference to the compound variable
                     or  type.  When a discipline function is invoked, _ is initialized as a ref-
                     erence to the variable associated with the call to this  function.   Finally
                     when  _  is used as the name of the first variable of a type definition, the
                     new type is derived from the type of the first variable. (See Type Variables
                      below.)
              !      The  process  id or the pool name and job number of the last background com-
                     mand invoked or the most recent job put in the background with the bg built-
                     in  command.   Background  jobs  started in a named pool will be in the form
                     pool.number where pool is the pool name and number is the job number  within
                     that pool.
              .sh.command
                     When  processing  a  DEBUG  trap, this variable contains the current command
                     line that is about to run.  The value is in the same format  as  the  output
                     generated by the xtrace option (minus the preceding PS4 prompt).
              .sh.edchar
                     This  variable  contains the value of the keyboard character (or sequence of
                     characters if the first character is an ESC, ASCII 033) that  has  been  en-
                     tered  when  processing a KEYBD trap (see Key Bindings below).  If the value
                     is changed as part of the trap action, then the new value replaces  the  key
                     (or key sequence) that caused the trap.
              .sh.edcol
                     The  character  position  of the cursor at the time of the most recent KEYBD
                     trap.
              .sh.edmode
                     The value is set to ESC when processing a KEYBD  trap  while  in  vi  insert
                     mode.   (See  Vi  Editing  Mode  below.)  Otherwise, .sh.edmode is null when
                     processing a KEYBD trap.
              .sh.edtext
                     The characters in the input buffer at the time  of  the  most  recent  KEYBD
                     trap.  The value is null when not processing a KEYBD trap.
              .sh.file
                     The pathname of the file that contains the current command.
              .sh.fun
                     The name of the current function that is being executed.
              .sh.level
                     Set  to the current function depth.  This can be changed inside a DEBUG trap
                     and will set the context to the specified level.
              .sh.lineno
                     Set during a DEBUG trap to the line number for the caller of each function.
              .sh.match
                     An indexed array which stores the most recent match and  subpattern  matches
                     after  conditional pattern matches that match and after variables expansions
                     using the operators #, %, or /.  The 0-th element stores the complete  match
                     and the i-th.  element stores the i-th submatch.  The .sh.match variable be-
                     comes unset when the variable that has expanded is assigned a new value.
              .sh.math
                     Used for defining arithmetic functions (see Arithmetic Evaluation below) and
                     stores the list of user defined arithmetic functions.
              .sh.name
                     Set  to  the  name of the variable at the time that a discipline function is
                     invoked.
              .sh.subscript
                     Set to the name subscript of the variable at  the  time  that  a  discipline
                     function is invoked.
              .sh.subshell
                     The current depth for subshells and command substitution.
              .sh.pid
                     Set  to the process ID of the current shell.  This is distinct from $$ as in
                     forked subshells this is set to the process ID of the  subshell  instead  of
                     the  parent  shell's  process  ID.  In virtual subshells .sh.pid retains its
                     previous value.
              .sh.value
                     Set to the value of the variable at the time that the set or  append  disci-
                     pline  function  is invoked.  When a user defined arithmetic function is in-
                     voked, the value of .sh.value is saved and .sh.value is set to  long  double
                     precision floating point.  .sh.value is restored when the function returns.
              .sh.version
                     Set to a value that identifies the version of this shell.
              KSH_VERSION
                     A name reference to .sh.version.
              LINENO The current line number within the script or function being executed.
              OLDPWD The previous working directory set by the cd command.
              OPTARG The value of the last option argument processed by the getopts built-in com-
                     mand.
              OPTIND The index of the last option argument processed by the getopts built-in com-
                     mand.
              PPID   The process id of the parent of the shell.
              PWD    The present working directory set by the cd command.
              RANDOM Each  time this variable is referenced, a random integer, uniformly distrib-
                     uted between 0 and 32767, is generated.  The sequence of random numbers  can
                     be initialized by assigning a numeric value to RANDOM.
              REPLY  This  variable  is set by the select statement and by the read built-in com-
                     mand when no arguments are supplied.
              SECONDS
                     Each time this variable is referenced, the number of seconds since shell in-
                     vocation  is returned.  If this variable is assigned a value, then the value
                     returned upon reference will be the value that was assigned plus the  number
                     of seconds since the assignment.
              SHLVL  An  integer variable that is incremented and exported each time the shell is
                     invoked.  If SHLVL is not in the environment when the shell is  invoked,  it
                     is set to 1.

       The following variables are used by the shell:
              CDPATH The search path for the cd command.
              COLUMNS
                     If  this  variable is set, the value is used to define the width of the edit
                     window for the shell edit modes and for printing select lists.
              EDITOR If the VISUAL variable is not set,  the  value  of  this  variable  will  be
                     checked  for the patterns as described with VISUAL below and the correspond-
                     ing editing option (see Special Command set below) will be turned on.
              ENV    If this variable is set, then parameter expansion, command substitution, and
                     arithmetic  expansion are performed on the value to generate the pathname of
                     the script that will be executed when the  shell  is  invoked  interactively
                     (see  Invocation below).  This file is typically used for alias and function
                     definitions.  The default value is $HOME/.kshrc.  On systems that support  a
                     system  wide   /etc/ksh.kshrc initialization file, if the filename generated
                     by the expansion of ENV begins with /./ or ././ the system wide  initializa-
                     tion file will not be executed.
              FCEDIT Obsolete  name  for the default editor name for the hist command.  FCEDIT is
                     not used when HISTEDIT is set.
              FIGNORE
                     A pattern that defines the set of filenames that will be ignored  when  per-
                     forming filename matching.
              FPATH  The  search path for function definitions.  The directories in this path are
                     searched for a file with the same name as the function  or  command  when  a
                     function  with  the  -u  attribute  is  referenced and when a command is not
                     found.  If an executable file with the name of that command is  found,  then
                     it  is  read and executed in the current environment.  Unlike PATH, the cur-
                     rent directory must be represented explicitly by .  rather than by  adjacent
                     : characters or a beginning or ending :.
              HISTCMD
                     Number of the current command in the history file.
              HISTEDIT
                     Name for the default editor name for the hist command.
              HISTFILE
                     If  this  variable  is  set when the shell is invoked, then the value is the
                     pathname of the file that will be used to store  the  command  history  (see
                     Command Re-entry below).
              HISTSIZE
                     If this variable is set when the shell is invoked, then the number of previ-
                     ously entered commands that are accessible by this  shell  will  be  greater
                     than or equal to this number.  The default is 512.
              HOME   The default argument (home directory) for the cd command.
              IFS    Internal  field  separators, normally space, tab, and new-line that are used
                     to separate the results of command substitution or parameter  expansion  and
                     to  separate  fields with the built-in command read.  The first character of
                     the IFS variable is used to separate arguments for the "$*"  expansion  (see
                     Quoting below).  Each single occurrence of an IFS character in the string to
                     be split, that is not in the isspace character class, and any adjacent char-
                     acters in IFS that are in the isspace character class, delimit a field.  One
                     or more characters in IFS that belong to the isspace  character  class,  de-
                     limit  a field.  In addition, if the same isspace character appears consecu-
                     tively inside IFS, this character is treated as if it were not in  the  iss-
                     pace class, so that if IFS consists of two tab characters, then two adjacent
                     tab characters delimit a null field.
              JOBMAX This variable defines the maximum number running background  jobs  that  can
                     run at a time.  When this limit is reached, the shell will wait for a job to
                     complete before starting a new job.
              LANG   This variable determines the locale category for any category  not  specifi-
                     cally selected with a variable starting with LC_ or LANG.
              LC_ALL This  variable  overrides  the  value of the LANG variable and any other LC_
                     variable.
              LC_COLLATE
                     This variable determines the locale category for character collation  infor-
                     mation.
              LC_CTYPE
                     This  variable  determines  the locale category for character handling func-
                     tions.  It determines the character classes for pattern matching (see  Path-
                     name Expansion below).
              LC_NUMERIC
                     This  variable  determines the locale category for the decimal point charac-
                     ter.
              LINES  If this variable is set, the value is used to determine  the  column  length
                     for  printing  select lists.  Select lists will print vertically until about
                     two-thirds of LINES lines are filled.
              MAIL   If this variable is set to the name of a mail file and the MAILPATH variable
                     is not set, then the shell informs the user of arrival of mail in the speci-
                     fied file.
              MAILCHECK
                     This variable specifies how often (in seconds)  the  shell  will  check  for
                     changes  in the modification time of any of the files specified by the MAIL-
                     PATH or MAIL variables.  The default value is 600 seconds.   When  the  time
                     has elapsed the shell will check before issuing the next prompt.
              MAILPATH
                     A  colon  ( : ) separated list of file names.  If this variable is set, then
                     the shell informs the user of any modifications to the specified files  that
                     have occurred within the last MAILCHECK seconds.  Each file name can be fol-
                     lowed by a ?  and a message that will be printed.  The message will  undergo
                     parameter expansion, command substitution, and arithmetic expansion with the
                     variable $_ defined as the name of the file that has changed.   The  default
                     message is you have mail in $_.
              PATH   The search path for commands (see Execution below).  The user may not change
                     PATH if executing under rksh (except in .profile).
              PS1    Every time a new command line is started on an interactive shell, the  value
                     of this variable is expanded to resolve backslash escaping, parameter expan-
                     sion, command substitution, and arithmetic expansion.   The  result  defines
                     the  primary  prompt  string  for that command line.  The default is ``$ ''.
                     The character !  in the primary prompt string is  replaced  by  the  command
                     number  (see Command Re-entry below).  Two successive occurrences of !  will
                     produce a single !  when the prompt string is printed.  Note that any termi-
                     nal  escape  sequences  used in the PS1 prompt thus need every instance of !
                     in them to be changed to !!.
              PS2    Secondary prompt string, by default ``> ''.
              PS3    Selection prompt string used within a select loop, by default ``#? ''.
              PS4    The value of this variable is expanded  for  parameter  evaluation,  command
                     substitution,  and  arithmetic expansion and precedes each line of an execu-
                     tion trace.  By default, PS4 is ``+ ''.  In addition when PS4 is unset,  the
                     execution trace prompt is also ``+ ''.
              SHELL  The pathname of the shell is kept in the environment.  At invocation, if the
                     basename of this variable is rsh, rksh, or krsh, then the shell becomes  re-
                     stricted.
              TIMEFORMAT
                     The  value  of  this parameter is used as a format string specifying how the
                     timing information for pipelines prefixed with the time reserved word should
                     be displayed.  The % character introduces a format sequence that is expanded
                     to a time value or other information.  The format sequences and their  mean-
                     ings are as follows.
                     %%        A literal %.
                     %[p][l]R  The elapsed time in seconds.
                     %[p][l]U  The number of CPU seconds spent in user mode.
                     %[p][l]S  The number of CPU seconds spent in system mode.
                     %P        The CPU percentage, computed as (U + S) / R.

                     The brackets denote optional portions.  The optional p is a digit specifying
                     the precision, the number of fractional digits after  a  decimal  point.   A
                     value  of 0 causes no decimal point or fraction to be output.  At most three
                     places after the decimal point can be displayed; values of p greater than  3
                     are treated as 3.  If p is not specified, the value 3 is used.

                     The  optional  l  specifies a longer format, including hours if greater than
                     zero, minutes, and seconds of the form HHhMMmSS.FFs.  The value of p  deter-
                     mines whether or not the fraction is included.

                     All  other  characters  are  output without change and a trailing newline is
                     added.  If unset, the default value, $'\nreal\t%2lR\nuser\t%2lU\nsys\t%2lS',
                     is used.  If the value is null, no timing information is displayed.

              TMOUT  Terminal  read timeout. If set to a value greater than zero, the read built-
                     in command and the select compound command time out after TMOUT seconds when
                     input is from a terminal.  An interactive shell will issue a warning and al-
                     low for an extra 60 second timeout grace period before terminating if a line
                     is  not entered within the prescribed number of seconds while reading from a
                     terminal.  (Note that the shell can be compiled with  a  maximum  bound  for
                     this value which cannot be exceeded.)

              VISUAL If  the  value  of this variable matches the pattern *[Vv][Ii]*, then the vi
                     option (see Special Command set below) is turned on.  If the  value  matches
                     the  pattern  *gmacs* , the gmacs option is turned on.  If the value matches
                     the pattern *macs*, then the emacs option will be turned on.  The  value  of
                     VISUAL overrides the value of EDITOR.

       The  shell  gives default values to PATH, PS1, PS2, PS3, PS4, MAILCHECK, FCEDIT, TMOUT and
       IFS, while HOME, SHELL, ENV, and MAIL are not set at all by the shell  (although  HOME  is
       set by login(1)).  On some systems MAIL and SHELL are also set by login(1).

   Field Splitting.
       After  parameter  expansion  and  command  substitution,  the results of substitutions are
       scanned for the field separator characters (those found in IFS) and  split  into  distinct
       fields  where  such  characters  are found.  Explicit null fields ("" or '') are retained.
       Implicit null fields (those resulting from parameters that have no values or command  sub-
       stitutions with no output) are removed.

   Brace Expansion.
       If  the  braceexpand  (-B)  option  is  set then each of the fields resulting from IFS are
       checked to see if they contain one or  more  of  the  brace  patterns  {*,*},  {l1..l2}  ,
       {n1..n2}  ,  {n1..n2% fmt} , {n1..n2 ..n3} , or {n1..n2 ..n3%fmt} , where * represents any
       character, l1,l2 are letters and n1,n2,n3 are signed numbers and fmt is a format specified
       as  used  by printf.  In each case, fields are created by prepending the characters before
       the { and appending the characters after the } to each of the  strings  generated  by  the
       characters  between the { and }.  The resulting fields are checked to see if they have any
       brace patterns.

       In the first form, a field is created for each string between { and ,, between  ,  and  ,,
       and  between  ,  and }.  The string represented by * can contain embedded matching { and }
       without quoting.  Otherwise, each { and } with * must be quoted.

       In the seconds form, l1 and l2 must both be either upper case or both be lower case  char-
       acters  in  the C locale.  In this case a field is created for each character from l1 thru
       l2.

       In the remaining forms, a field is created for each number starting at n1  and  continuing
       until  it reaches n2 incrementing n1 by n3.  The cases where n3 is not specified behave as
       if n3 where 1 if n1<=n2 and -1 otherwise.  If forms which specify %fmt any  format  flags,
       widths  and  precisions can be specified and fmt can end in any of the specifiers cdiouxX.
       For example, {a,z}{1..5..3%02d}{b..c}x expands to  the  8  fields,  a01bx,  a01cx,  a04bx,
       a04cx, z01bx, z01cx, z04bx and z04cx.

   Pathname Expansion.
       This  is  also  known  as globbing or sometimes filename generation.  Following splitting,
       each field is scanned for the characters *, ?, (, and [ unless the -f option has been set.
       If  one  of  these  characters appears, then the word is regarded as a pattern.  Each file
       name component that contains any pattern character is replaced  with  a  lexicographically
       sorted  set  of  names  that  matches the pattern from that directory.  If no file name is
       found that matches the pattern, then that component of the filename is left unchanged  un-
       less  the  pattern  is  prefixed with ~(N) in which case it is removed as described below.
       The special traversal names .  and ..  are never matched.  If FIGNORE is  set,  then  each
       file  name  component  that matches the pattern defined by the value of FIGNORE is ignored
       when generating the matching filenames.  If FIGNORE is not set, the character  .   at  the
       start  of  each file name component will be ignored unless the first character of the pat-
       tern corresponding to this component is the character .  itself.   Note,  that  for  other
       uses of pattern matching the / and .  are not treated specially.

              *      Matches  any  string, including the null string.  When used for filename ex-
                     pansion, if the globstar option is on, an isolated pattern of  two  adjacent
                     *'s  will  match  all files and zero or more directories and subdirectories.
                     If followed by a / then only directories and subdirectories will match.
              ?      Matches any single character.
              [...]  Matches any one of the enclosed characters.  A pair of characters  separated
                     by  -  matches  any character lexically between the pair, inclusive.  If the
                     first character following the opening [ is a !  or ^ then any character  not
                     enclosed is matched.  A - can be included in the character set by putting it
                     as the first or last character.
                     Within [ and ], character classes can be specified with the syntax [:class:]
                     where  class is one of the following classes defined in the ANSI C standard:
                     (Note that word is equivalent to alnum plus the character _.)
                     alnum alpha blank cntrl digit graph  lower  print  punct  space  upper  word
                     xdigit
                     Within  [ and ], an equivalence class can be specified with the syntax [=c=]
                     which matches all characters with the same primary collation weight (as  de-
                     fined by the current locale) as the character c.  Within [ and ], [.symbol.]
                     matches the collating symbol symbol.
       A pattern-list is a list of one or more patterns separated from each other with a & or  |.
       A  &  signifies that all patterns must be matched whereas | requires that only one pattern
       be matched.  Composite patterns can be formed with one or more of  the  following  subpat-
       terns:
              ?(pattern-list)
                     Optionally matches any one of the given patterns.
              *(pattern-list)
                     Matches zero or more occurrences of the given patterns.
              +(pattern-list)
                     Matches one or more occurrences of the given patterns.
              {n}(pattern-list)
                     Matches n occurrences of the given patterns.
              {m,n}(pattern-list)
                     Matches  from  m to n occurrences of the given patterns.  If m is omitted, 0
                     will be used.  If n is omitted at least m occurrences will be matched.
              @(pattern-list)
                     Matches exactly one of the given patterns.
              !(pattern-list)
                     Matches anything except one of the given patterns.
       By default, each pattern, or subpattern will match the longest string possible  consistent
       with  generating  the  longest overall match.  If more than one match is possible, the one
       starting closest to the beginning of the string will be chosen.   However, for each of the
       above  compound patterns a - can be inserted in front of the ( to cause the shortest match
       to the specified pattern-list to be used.

       When pattern-list is contained within parentheses, the backslash character  \  is  treated
       specially  even  when  inside a character class.   All ANSI C character escapes are recog-
       nized and match the specified character.  In addition the following escape  sequences  are
       recognized:
              \d     Matches any character in the digit class.
              \D     Matches any character not in the digit class.
              \s     Matches any character in the space class.
              \S     Matches any character not in the space class.
              \w     Matches any character in the word class.
              \W     Matches any character not in the word class.

       A  pattern of the form %(pattern-pair(s)) is a subpattern that can be used to match nested
       character expressions.  Each pattern-pair is a two character sequence which cannot contain
       &  or  |.   The  first  pattern-pair  specifies the starting and ending characters for the
       match.  Each subsequent pattern-pair represents the beginning and ending characters  of  a
       nested  group  that  will  be  skipped  over  when  counting starting and ending character
       matches.  The behavior is unspecified when the first character of a  pattern-pair  is  al-
       phanumeric except for the following:
              D      Causes the ending character to terminate the search for this pattern without
                     finding a match.
              E      Causes the ending character to be interpreted as an escape character.
              L      Causes the ending character to be interpreted as a quote  character  causing
                     all characters to be ignored when looking for a match.
              Q      Causes  the  ending character to be interpreted as a quote character causing
                     all characters other than any escape character to be  ignored  when  looking
                     for a match.
       Thus, %({}Q"E\), matches characters starting at { until the matching } is found not count-
       ing any { or } that is inside a double quoted string or preceded by the  escape  character
       \.  Without the {} this pattern matches any C language string.

       Each  subpattern in a composite pattern is numbered, starting at 1, by the location of the
       ( within the pattern.  The sequence \n, where n is a single digit and \n comes  after  the
       n-th. subpattern, matches the same string as the subpattern itself.

       Finally  a  pattern can contain subpatterns of the form ~(options:pattern-list), where ei-
       ther options or :pattern-list can be omitted.  Unlike the other compound  patterns,  these
       subpatterns  are  not  counted in the numbered subpatterns.  :pattern-list must be omitted
       for options F, G, N , and V below.  If options is present, it can consist of one  or  more
       of the following:
              +      Enable the following options.  This is the default.
              -      Disable the following options.
              E      The  remainder  of  the pattern uses extended regular expression syntax like
                     the egrep(1) command.
              F      The remainder of the pattern uses fgrep(1) expression syntax.
              G      The remainder of the pattern uses basic regular expression syntax  like  the
                     grep(1) command.
              K      The  remainder  of  the  pattern uses shell pattern syntax.  This is the de-
                     fault.
              N      This is ignored.  However, when it is the first  letter  and  is  used  with
                     pathname  expansion,  and  no matches occur, the file pattern expands to the
                     empty string.
              X      The remainder of the pattern uses augmented regular expression  syntax  like
                     the xgrep(1) command.
              P      The  remainder  of  the pattern uses perl(1) regular expression syntax.  Not
                     all perl regular expression syntax is currently implemented.
              V      The remainder of the pattern uses System V regular expression syntax.
              i      Always treat the match as case-insensitive, regardless of the globcasedetect
                     shell option.
              g      File the longest match (greedy).  This is the default.
              l      Left anchor the pattern.  This is the default for K style patterns.
              r      Right anchor the pattern.  This is the default for K style patterns.
       If  both options and :pattern-list are specified, then the options apply only to  pattern-
       list.  Otherwise, these options remain in effect until they are disabled by  a  subsequent
       ~(...) or at the end of the subpattern containing ~(...).

   Quoting.
       Each of the metacharacters listed earlier (see Definitions above) has a special meaning to
       the shell and causes termination of a word unless  quoted.   A  character  may  be  quoted
       (i.e., made to stand for itself) by preceding it with a \.  The pair \new-line is removed.
       All characters enclosed between a pair of single quote marks ('') that is not preceded  by
       a  $  are quoted.  A single quote cannot appear within the single quotes.  A single quoted
       string preceded by an unquoted $ is processed as an ANSI C string except for  the  follow-
       ing:
       \0     Causes the remainder of the string to be ignored.
       \E     Equivalent to the escape character (ASCII 033),
       \e     Equivalent to the escape character (ASCII 033),
       \cx    Expands to the character control-x.
       \C[.name.]
              Expands to the collating element name.

       Inside  double quote marks (""), parameter and command substitution occur and \ quotes the
       characters \, `, ", and $.  A $ in front of a double quoted string will be ignored in  the
       "C" or "POSIX" locale, and may cause the string to be replaced by a locale specific string
       otherwise.  The meaning of $* and $@ is identical when not quoted or when used as a  vari-
       able  assignment  value or as a file name.  However, when used as a command argument, "$*"
       is equivalent to "$1d$2d...", where d is the first character of the IFS variable,  whereas
       "$@"  is equivalent to "$1" "$2" ....  Inside grave quote marks (``), \ quotes the charac-
       ters \, `, and $.  If the grave quotes occur within double quotes, then \ also quotes  the
       character ".

       The  special  meaning of reserved words or aliases can be removed by quoting any character
       of the reserved word.  The recognition of function names or built-in command names  listed
       below cannot be altered by quoting them.

   Arithmetic Evaluation.
       The  shell  performs arithmetic evaluation for arithmetic expansion, to evaluate an arith-
       metic command, to evaluate an indexed array subscript, and to evaluate  arguments  to  the
       built-in commands shift and let as well as arguments to numeric format specifiers given to
       print -f  and printf.  Evaluations are performed using  double  precision  floating  point
       arithmetic  or  long  double  precision  floating point for systems that provide this data
       type.  Floating point constants follow the ANSI C programming language floating point con-
       ventions.  The case-insensitive floating point constants NaN and Inf can be used to repre-
       sent "not a number" and infinity respectively, unless the posix shell option is on.  Inte-
       ger constants follow the ANSI C programming language integer constant conventions although
       only single byte character constants are recognized and character  casts  are  not  recog-
       nized.   In  addition constants can be of the form [base#]n where base is a decimal number
       between two and sixty-four representing the arithmetic base and n  is  a  number  in  that
       base.   The  digits above 9 are represented by the lower case letters, the upper case let-
       ters, @, and _ respectively.  For bases less than or equal to 36,  upper  and  lower  case
       characters can be used interchangeably.

       An arithmetic expression uses the same syntax, precedence, and associativity of expression
       as the C language.  All the C language operators that apply to floating  point  quantities
       can  be used.  In addition, the operator ** can be used for exponentiation.  It has higher
       precedence than multiplication and is left associative.  In addition, when the value of an
       arithmetic  variable or subexpression can be represented as a long integer, all C language
       integer arithmetic operations can be performed.   Variables  can  be  referenced  by  name
       within  an  arithmetic  expression  without  using the parameter expansion syntax.  When a
       variable is referenced, its value is evaluated as an arithmetic expression.

       Any of the following math library functions that are in the C math  library  can  be  used
       within an arithmetic expression:

       abs  acos acosh asin asinh atan atan2 atanh cbrt ceil copysign cos cosh erf erfc exp exp10
       exp2 expm1 fabs fdim finite float floor fma fmax fmin fmod fpclass fpclassify hypot  ilogb
       int  isfinite  isgreater  isgreaterequal isinf isinfinite isless islessequal islessgreater
       isnan isnormal issubnormal isunordered iszero j0 j1 jn ldexp lgamma log log10  log1p  log2
       logb nearbyint nextafter nexttoward pow remainder rint round scalb scalbn signbit sin sinh
       sqrt tan tanh tgamma trunc y0 y1 yn

       In addition, arithmetic functions can be defined as shell functions with a variant of  the
       function name syntax,

       function .sh.math.name ident ... { list ;}
              where  name is the function name used in the arithmetic expression and each identi-
              fier, ident is a name reference to the long double precision floating  point  argu-
              ment.   The value of .sh.value when the function returns is the value of this func-
              tion.  User defined functions can take up to 3 arguments and override  C  math  li-
              brary functions.

       An internal representation of a variable as a double precision floating point can be spec-
       ified with the -E [n], -F [n], or -X [n] option of the typeset special  built-in  command.
       The  -E  option causes the expansion of the value to be represented using scientific nota-
       tion when it is expanded.  The optional option argument n defines the number  of  signifi-
       cant  figures.  The -F option causes the expansion to be represented as a floating decimal
       number when it is expanded.  The -X option causes the expansion to  be  represented  using
       the  %a  format defined by ISO C-99.  The optional option argument n defines the number of
       places after the decimal (or radix) point in this case.

       An internal integer representation of a variable can be specified with the -i  [n]  option
       of  the  typeset  special  built-in  command.  The optional option argument n specifies an
       arithmetic base to be used when expanding the variable.  If you do not specify  an  arith-
       metic base, base 10 will be used.

       Arithmetic  evaluation is performed on the value of each assignment to a variable with the
       -E, -F, -X, or -i attribute.  Assigning a floating point number to a variable  whose  type
       is an integer causes the fractional part to be truncated.

   Prompting.
       When  used  interactively,  the shell prompts with the value of PS1 after expanding it for
       parameter expansion, command substitution, and arithmetic expansion, before reading a com-
       mand.   In addition, each single !  in the prompt is replaced by the command number.  A !!
       is required to place !  in the prompt.  If at any time a new-line is typed and further in-
       put is needed to complete a command, then the secondary prompt (i.e., the value of PS2) is
       issued.

   Conditional Expressions.
       A conditional expression is used with the [[ compound command to test attributes of  files
       and  to  compare strings.  Field splitting and pathname expansion are not performed on the
       words between [[ and ]].  Each expression can be constructed from one or more of the  fol-
       lowing unary or binary expressions:
       string True, if string is not null.
       -a file
              Same as -e below.  This is obsolete.
       -b file
              True, if file exists and is a block special file.
       -c file
              True, if file exists and is a character special file.
       -d file
              True, if file exists and is a directory.
       -e file
              True, if file exists.
       -f file
              True, if file exists and is an ordinary file.
       -g file
              True, if file exists and it has its setgid bit set.
       -k file
              True, if file exists and it has its sticky bit set.
       -n string
              True, if length of string is non-zero.
       -o ?option
              True, if option named option is a valid option name.
       -o option
              True, if option named option is on.
       -p file
              True, if file exists and is a fifo special file or a pipe.
       -r file
              True, if file exists and is readable by current process.
       -s file
              True, if file exists and has size greater than zero.
       -t fildes
              True,  if  file descriptor number fildes is open and associated with a terminal de-
              vice.
       -u file
              True, if file exists and it has its setuid bit set.
       -v name
              True, if variable name is a valid variable name and is set.
       -w file
              True, if file exists and is writable by current process.
       -x file
              True, if file exists and is executable by current process.  If file exists and is a
              directory,  then true if the current process has permission to search in the direc-
              tory.
       -z string
              True, if length of string is zero.
       -L file
              True, if file exists and is a symbolic link.
       -h file
              True, if file exists and is a symbolic link.
       -N file
              True, if file exists and the modification time is  greater  than  the  last  access
              time.
       -O file
              True, if file exists and is owned by the effective user id of this process.
       -G file
              True, if file exists and its group matches the effective group id of this process.
       -R name
              True if variable name is a name reference.
       -S file
              True, if file exists and is a socket.
       file1 -nt file2
              True, if file1 exists and file2 does not, or file1 is newer than file2.
       file1 -ot file2
              True, if file2 exists and file1 does not, or file1 is older than file2.
       file1 -ef file2
              True, if file1 and file2 exist and refer to the same file.
       string == pattern
              True,  if string matches pattern.  Any part of pattern can be quoted to cause it to
              be matched as a string.  With a successful match to a pattern, the .sh.match  array
              variable will contain the match and subpattern matches.
       string = pattern
              Same as == above, but is obsolete.
       string != pattern
              True,  if  string  does not match pattern.  When the string matches the pattern the
              .sh.match array variable will contain the match and subpattern matches.
       string =~ ere
              True if string matches the pattern ~(E)ere where ere is an extended regular expres-
              sion.
       string1 < string2
              True, if string1 comes before string2 based on ASCII value of their characters.
       string1 > string2
              True, if string1 comes after string2 based on ASCII value of their characters.
       The following obsolete arithmetic comparisons are also permitted:
       exp1 -eq exp2
              True, if exp1 is equal to exp2.
       exp1 -ne exp2
              True, if exp1 is not equal to exp2.
       exp1 -lt exp2
              True, if exp1 is less than exp2.
       exp1 -gt exp2
              True, if exp1 is greater than exp2.
       exp1 -le exp2
              True, if exp1 is less than or equal to exp2.
       exp1 -ge exp2
              True, if exp1 is greater than or equal to exp2.

       In each of the above expressions, if file is of the form /dev/fd/n, where n is an integer,
       then the test is applied to the open file whose descriptor number is n.

       A compound expression can be constructed from these primitives by using any of the follow-
       ing, listed in decreasing order of precedence.
       (expression)
              True, if expression is true.  Used to group expressions.
       ! expression
              True if expression is false.
       expression1 && expression2
              True, if expression1 and expression2 are both true.
       expression1 || expression2
              True, if either expression1 or expression2 is true.

   Input/Output.
       Before a command is executed, its input and output may be redirected using a special nota-
       tion interpreted by the shell.  The following may appear anywhere in a  simple-command  or
       may  precede  or  follow  a command and are not passed on to the invoked command.  Command
       substitution, parameter expansion, and arithmetic expansion occur before word or digit  is
       used  except  as  noted below.  Pathname expansion occurs only if the shell is interactive
       and the pattern matches a single file.  Field splitting is not performed.

       In each of the following  redirections,  if  file  is  of  the  form  /dev/sctp/host/port,
       /dev/tcp/host/port,  or  /dev/udp/host/port, where host is a hostname or host address, and
       port is a service given by name or an integer port number, then the  redirection  attempts
       to make a tcp, sctp or udp connection to the corresponding socket.

       No intervening space is allowed between the characters of redirection operators.

       <word         Use file word as standard input (file descriptor 0).

       >word         Use  file word as standard output (file descriptor 1).  If the file does not
                     exist then it is created.  If the file exists, and the noclobber  option  is
                     on, this causes an error; otherwise, it is truncated to zero length.

       >|word        Same as >, except that it overrides the noclobber option.

       >;word        Write output to a temporary file.  If the command completes successfully re-
                     name it to word, otherwise, delete the temporary  file.   >;word  cannot  be
                     used with the exec and redirect built-ins.

       >>word        Use  file  word  as standard output.  If the file exists, then output is ap-
                     pended to it (by first seeking to the end-of-file); otherwise, the  file  is
                     created.

       <>word        Open file word for reading and writing as standard output.  If the posix op-
                     tion is active, it defaults to standard input instead.

       <>;word       The same as <>word except that if the command completes  successfully,  word
                     is  truncated  to  the offset at command completion.  <>;word cannot be used
                     with the exec and redirect built-ins.

       <<[-]word     The shell input is read up to a line that is the  same  as  word  after  any
                     quoting  has  been  removed,  or to an end-of-file.  No parameter expansion,
                     command substitution, arithmetic expansion or  pathname  expansion  is  per-
                     formed on word.  The resulting document, called a here-document, becomes the
                     standard input.  If any character of word is quoted, then no  interpretation
                     is  placed  upon the characters of the document; otherwise, parameter expan-
                     sion, command substitution, and arithmetic expansion occur, \new-line is ig-
                     nored, and \ must be used to quote the characters \, $, `.  If - is appended
                     to <<, then all leading tabs are stripped from word and from  the  document.
                     If  #  is  appended to <<, then leading spaces and tabs will be stripped off
                     the first line of the document and up to an equivalent indentation  will  be
                     stripped  from  the remaining lines and from word.  A tab stop is assumed to
                     occur at every 8 columns for the purposes of determining the indentation.

       <<<word       A short form of here document in which word  becomes  the  contents  of  the
                     here-document  after  any  parameter  expansion,  command  substitution, and
                     arithmetic expansion occur.

       <&digit       The standard input is duplicated from file descriptor digit (see dup(2)).

       >&digit       The standard output is duplicated from file descriptor digit.

       <&digit-      The file descriptor given by digit is moved to standard input.

       >&digit-      The file descriptor given by digit is moved to standard output.

       <&-           The standard input is closed.

       >&-           The standard output is closed.

       <&p           The input from the co-process is moved to standard input.

       >&p           The output to the co-process is moved to standard output.

       <#((expr))    Evaluate arithmetic expression expr and position file descriptor  0  to  the
                     resulting value bytes from the start of the file.  The variables CUR and EOF
                     evaluate to the current offset  and  end-of-file  offset  respectively  when
                     evaluating expr.

       >#((offset))  The same as <# except applies to file descriptor 1.

       <#pattern     Seeks forward to the beginning of the next line containing pattern.

       <##pattern    The same as <# except that the portion of the file that is skipped is copied
                     to standard output.

       If one of the above is preceded by a digit, with no intervening space, then the  file  de-
       scriptor  number  referred  to is that specified by the digit (instead of the default 0 or
       1).  If one of the above, other than >&- and the ># and <# forms, is preceded by {varname}
       with no intervening space, then a file descriptor number > 9 will be selected by the shell
       and stored in the variable varname, so it can be read from or written to with redirections
       like  <& $varname or >& $varname.  If >&- or the any of the ># and <# forms is preceded by
       {varname} the value of varname defines the file descriptor to close or position.  For  ex-
       ample:

              ... 2>&1

       means  file  descriptor  2 is to be opened for writing as a duplicate of file descriptor 1
       and

              exec {n}<file

       means open file named file for reading and store the file descriptor number in variable n.

       A special shorthand redirection operator &>word is available; it is  equivalent  to  >word
       2>&1.  It  cannot be preceded by any digit or variable name. This shorthand is disabled if
       the posix shell option is active.

       The order in which redirections are specified is significant.  The  shell  evaluates  each
       redirection in terms of the (file descriptor, file) association at the time of evaluation.
       For example:

              ... 1>fname 2>&1

       first associates file descriptor 1 with file fname.  It then associates file descriptor  2
       with  the  file associated with file descriptor 1 (i.e.  fname).  If the order of redirec-
       tions were reversed, file descriptor 2 would be associated  with  the  terminal  (assuming
       file  descriptor  1  had  been)  and  then file descriptor 1 would be associated with file
       fname.

       If a command is followed by & and job control is not active, then the default standard in-
       put  for the command is the empty file /dev/null.  Otherwise, the environment for the exe-
       cution of a command contains the file descriptors of the invoking shell as modified by in-
       put/output specifications.

   Environment.
       The  environment  (see environ(7)) is a list of name-value pairs that is passed to an exe-
       cuted program in the same way as a normal argument list.  The names  must  be  identifiers
       and the values are character strings.  The shell interacts with the environment in several
       ways.  On invocation, the shell scans the environment and creates a variable for each name
       found,  giving  it the corresponding value and attributes and marking it export.  Executed
       commands inherit the environment.  If the user modifies the values of these  variables  or
       creates  new  ones, using the export or typeset -x commands, they become part of the envi-
       ronment.  The environment seen by any executed command is thus composed of any  name-value
       pairs  originally  inherited  by  the  shell,  whose values may be modified by the current
       shell, plus any additions which must be noted in export or typeset -x commands.

       The environment for any simple-command or function may be augmented by prefixing  it  with
       one  or  more  variable assignments.  A variable assignment argument is a word of the form
       identifier=value.  Thus:

              TERM=450 cmd args                  and
              (export TERM; TERM=450; cmd args)

       are equivalent (as far as the above execution of  cmd  is  concerned  except  for  special
       built-in commands listed below - those that are marked with <*>).

       If  the obsolete -k option is set, all variable assignment arguments are placed in the en-
       vironment, even if they occur after the command name.  The following first  prints  a=b  c
       and then c:

              echo a=b c
              set -k
              echo a=b c
       This  feature is intended for use with scripts written for early versions of the shell and
       its use in new scripts is strongly discouraged.  It is likely to disappear someday.

   Functions.
       For historical reasons, there are two ways to define functions, the name() syntax and  the
       function  name  syntax, described in the Commands section above.  Shell functions are read
       in and stored internally.  Alias names are resolved when the function is read.   Functions
       are  executed like commands with the arguments passed as positional parameters.  (See Exe-
       cution below.)

       Functions defined by the function name syntax and called  by  name  execute  in  the  same
       process  as  the caller and share all files and present working directory with the caller.
       Traps caught by the caller are reset to their default action inside the function.  A  trap
       condition  that  is not caught or ignored by the function causes the function to terminate
       and the condition to be passed on to the caller.  A trap on EXIT set inside a function  is
       executed in the environment of the caller after the function completes.  Ordinarily, vari-
       ables are shared between the calling program and the function.  However, the typeset  spe-
       cial  built-in command used within a function defines local variables whose scope includes
       the current function.  They can be passed to functions that they call in the variable  as-
       signment  list  that  precedes the call or as arguments passed as name references.  Errors
       within functions return control to the caller.

       Functions defined with the name() syntax and functions defined with the function name syn-
       tax that are invoked with the .  special built-in are executed in the caller's environment
       and share all variables and traps with the caller.  Errors within  these  function  execu-
       tions cause the script that contains them to abort.

       The special built-in command return is used to return from function calls.

       Function names can be listed with the -f or +f option of the typeset special built-in com-
       mand.  The text of functions, when available, will also be listed with -f.  Functions  can
       be undefined with the -f option of the unset special built-in command.

       Ordinarily,  functions  are  unset when the shell executes a shell script.  Functions that
       need to be defined across separate invocations of the shell should be placed in  a  direc-
       tory  and  the FPATH variable should contain the name of this directory.  They may also be
       specified in the ENV file.

   Discipline Functions.
       Each variable can have zero or more discipline functions associated with  it.   The  shell
       initially  understands  the  discipline names get, set, append, and unset but can be added
       when defining new types.  On most systems others can be added at run time via the  C  pro-
       gramming  interface extension provided by the builtin built-in utility.  If the get disci-
       pline is defined for a variable, it is invoked whenever the given variable is  referenced.
       If  the  variable .sh.value is assigned a value inside the discipline function, the refer-
       enced variable will evaluate to this value instead.  If the set discipline is defined  for
       a  variable, it is invoked whenever the given variable is assigned a value.  If the append
       discipline is defined for a variable, it is invoked whenever a value is  appended  to  the
       given variable.  The variable .sh.value is given the value of the variable before invoking
       the discipline, and the variable will be assigned the value of .sh.value after the  disci-
       pline  completes.   If  .sh.value  is  unset inside the discipline, then that value is un-
       changed.  If the unset discipline is defined for a variable, it is  invoked  whenever  the
       given  variable  is  unset.   The variable will not be unset unless it is unset explicitly
       from within this discipline function.

       The variable .sh.name contains the name of the variable for which the discipline  function
       is  called, .sh.subscript is the subscript of the variable, and .sh.value will contain the
       value being assigned inside the set discipline function.  The variable _ is a reference to
       the  variable  including the subscript if any.  For the set discipline, changing .sh.value
       will change the value that gets assigned.  Finally, the expansion ${var.name},  when  name
       is  the  name of a discipline, and there is no variable of this name, is equivalent to the
       command substitution ${ var.name;}.

   Name Spaces.
       Commands and functions that are executed as part of the list of a namespace  command  that
       modify  variables  or create new ones, create a new variable whose name is the name of the
       name space as given by identifier preceded by ..  When a variable whose name  is  name  is
       referenced,  it  is  first searched for using .identifier.name.  Similarly, a function de-
       fined by a command in the namespace list is created using the name space name preceded  by
       a ..

       When  the list of a namespace command contains a namespace command, the names of variables
       and functions that are created consist of the variable or function name  preceded  by  the
       list of identifiers each preceded by ..

       Outside  of a name space, a variable or function created inside a name space can be refer-
       enced by preceding it with the name space name.

       By default, variables starting with .sh are in the sh name space.

   Type Variables.
       Typed variables provide a way to create data structure and objects.  A type can be defined
       either  by a shared library, by the enum built-in command described below, or by using the
       new -T option of the typeset built-in command.  With the -T option of  typeset,  the  type
       name,  specified  as  an option argument to -T, is set with a compound variable assignment
       that defines the type.  Function definitions can appear inside the compound  variable  as-
       signment  and  these become discipline functions for this type and can be invoked or rede-
       fined by each instance of the type.  The function name create is treated specially.  It is
       invoked  for  each instance of the type that is created but is not inherited and cannot be
       redefined for each instance.

       When a type is defined a special built-in command of that name is added.  These  built-ins
       are  declaration commands and follow the same expansion rules as the built-in commands de-
       scribed below that are marked with a <**> symbol. These commands can subsequently be  used
       inside  further type definitions.  The man page for these commands can be generated by us-
       ing the --man option or any of the other -- options described with getopts.  The  -r,  -a,
       -A, -h, and -S options of typeset are permitted with each of these new built-ins.

       An  instance  of  a  type is created by invoking the type name followed by one or more in-
       stance names.  Each instance of the type is initialized with a copy  of  the  subvariables
       except  for  subvariables that are defined with the -S option.  Variables defined with the
       -S are shared by all instances of the type.  Each instance can change  the  value  of  any
       subvariable  and  can  also define new discipline functions of the same names as those de-
       fined by the type definition as well as any standard discipline names.  No additional sub-
       variables can be defined for any instance.

       When  defining  a  type,  if the value of a subvariable is not set and the -r attribute is
       specified, it causes the subvariable to be a required subvariable.  Whenever  an  instance
       of a type is created, all required subvariables must be specified.  These subvariables be-
       come read-only in each instance.

       When unset is invoked on a subvariable within a type, and the -r attribute  has  not  been
       specified  for  this  field,  the value is reset to the default value associative with the
       type.  Invoking unset on a type instance not contained within  another  type  deletes  all
       subvariables and the variable itself.

       A  type  definition can be derived from another type definition by defining the first sub-
       variable name as _ and defining its type as the base type.  Any remaining definitions will
       be  additions  and  modifications that apply to the new type.  If the new type name is the
       same as that of the base type, the type will be replaced and the  original  type  will  no
       longer be accessible.

       The typeset command with the -T and no option argument or operands will write all the type
       definitions to standard output in a form that can be read in to create all they types.

   Jobs.
       If the monitor option of the set command is turned on, an interactive shell  associates  a
       job  with  each  pipeline.  It keeps a table of current jobs, printed by the jobs command,
       and assigns them small integer numbers.  When a job is started asynchronously with &,  the
       shell prints a line which looks like:

            [1] 1234

       indicating  that  the  job  which  was started asynchronously was job number 1 and had one
       (top-level) process, whose process id was 1234.

       This paragraph and the next require features that are not in all versions of UNIX and  may
       not  apply.  If you are running a job and wish to do something else you may hit the key ^Z
       (control-Z) which sends a STOP signal to the current job.  The shell  will  then  normally
       indicate  that the job has been `Stopped', and print another prompt.  You can then manipu-
       late the state of this job, putting it in the background with the bg command, or run  some
       other  commands  and then eventually bring the job back into the foreground with the fore-
       ground command fg.  A ^Z takes effect immediately and is like an interrupt in that pending
       output and unread input are discarded when it is typed.

       A  job being run in the background will stop if it tries to read from the terminal.  Back-
       ground jobs are normally allowed to produce output, but this can be disabled by giving the
       command stty tostop.  If you set this tty option, then background jobs will stop when they
       try to produce output like they do when they try to read input.

       A job pool is a collection of jobs started with list & associated with a name.

       There are several ways to refer to jobs in the shell.  A job can be  referred  to  by  the
       process id of any process of the job or by one of the following:
       %number
              The job with the given number.
       pool   All the jobs in the job pool named by pool.
       pool.number
              The job number number in the job pool named by pool.
       %string
              Any job whose command line begins with string.
       %?string
              Any job whose command line contains string.
       %%     Current job.
       %+     Equivalent to %%.
       %-     Previous  job.   In  addition, unless noted otherwise, wherever a job can be speci-
              fied, the name of a background job pool can be used to represent all  the  jobs  in
              that pool.

       The  shell  learns  immediately whenever a process changes state.  It normally informs you
       whenever a job becomes blocked so that no further progress is possible, but only just  be-
       fore  it  prints  a prompt.  This is done so that it does not otherwise disturb your work.
       The notify option of the set command causes the shell to print these job  change  messages
       as soon as they occur.

       When  the  monitor  option is on, each background job that completes triggers any trap set
       for CHLD.

       When you try to leave the shell while jobs are running or stopped, you will be warned that
       `You  have stopped(running) jobs.'  You may use the jobs command to see what they are.  If
       you immediately try to exit again, the shell will not warn you  a  second  time,  and  the
       stopped jobs will be terminated.  When a login shell receives a HUP signal, it sends a HUP
       signal to each job that has not been disowned with the disown built-in  command  described
       below.

   Signals.
       The  INT and QUIT signals for an invoked command are ignored if the command is followed by
       & and the monitor option is not active.  Otherwise, signals have the values  inherited  by
       the shell from its parent (but see also the trap built-in command below).

   Execution.
       Each  time  a command is read, the above expansions and substitutions are carried out.  If
       the command name matches one of the Special Built-in Commands listed below, it is executed
       within  the current shell process.  Next, the command name is checked to see if it matches
       a user defined function.  If it does, the positional parameters are saved and  then  reset
       to  the  arguments of the function call.  A function is also executed in the current shell
       process.  When the function completes or issues a return, the positional parameter list is
       restored.   For  functions  defined  with  the  function name syntax, any trap set on EXIT
       within the function is executed.  The exit value of a function is the value  of  the  last
       command  executed.   If a command name is not a special built-in command or a user defined
       function, but it is one of the built-in commands listed below, it is executed in the  cur-
       rent shell process.

       The shell variables PATH followed by the variable FPATH defines the list of directories to
       search for the command name.  Alternative directory names are separated by  a  colon  (:).
       The  default  path  is  the value that was output by getconf PATH at the time ksh was com-
       piled.  The current directory can be specified by two or more adjacent  colons,  or  by  a
       colon  at  the  beginning or end of the path list.  If the command name contains a /, then
       the search path is not used.  Otherwise, each directory in the list of directories defined
       by  PATH  and  FPATH is checked in order.  If the directory being searched is contained in
       FPATH and contains a file whose name matches the command being searched, then this file is
       loaded  into the current shell environment as if it were the argument to the . command ex-
       cept that only preset aliases are expanded, and a function of the given name  is  executed
       as described above.

       If  this  directory is not in FPATH the shell first determines whether there is a built-in
       version of a command corresponding to a given pathname and if so it is invoked in the cur-
       rent  process.   If no built-in is found, the shell checks for a file named .paths in this
       directory.  If found and there is a line of the form FPATH=path where path names an exist-
       ing  directory  then that directory is searched immediately after the current directory as
       if it were found in the FPATH variable.  If path does not begin with /, it is checked  for
       relative to the directory being searched.

       The  .paths  file  is then checked for a line of the form PLUGIN_LIB=libname [ : libname ]
       ... .  Each library named by libname will be searched for as if it were an option argument
       to  builtin  -f, and if it contains a built-in of the specified name this will be executed
       instead of a command by this name.  Any built-in loaded from a library found this way will
       be associated with the directory containing the .paths file so it will only execute if not
       found in an earlier directory.

       Finally, the directory will be checked for a file of the given name.  If the file has exe-
       cute permission but is not an a.out file, it is assumed to be a file containing shell com-
       mands.  A separate shell is spawned to read it.  All non-exported variables are removed in
       this  case.   If  the  shell  command  file doesn't have read permission, or if the setuid
       and/or setgid bits are set on the file, then the shell executes an agent whose job  it  is
       to set up the permissions and execute the shell with the shell command file passed down as
       an open file.  If the .paths contains a line of the form name=value in the first or second
       line, then the environment variable name is modified by prepending the directory specified
       by value to the directory list.  If value is not an absolute directory, then it  specifies
       a  directory  relative to the directory that the executable was found.  If the environment
       variable name does not already exist it will be added to  the  environment  list  for  the
       specified  command.   A  parenthesized  command is executed in a subshell without removing
       non-exported variables.

   Command Re-entry.
       The text of the last HISTSIZE (default 512) commands entered from  a  terminal  device  is
       saved  in  a history file.  The file $HOME/.sh_history is used if the HISTFILE variable is
       not set or if the file it names is not writable.  A shell can access the commands  of  all
       interactive  shells  which use the same named HISTFILE.  The built-in command hist is used
       to list or edit a portion of this file.  The portion of the file to be  edited  or  listed
       can  be  selected by number or by giving the first character or characters of the command.
       A single command or range of commands can be specified.  If you do not specify  an  editor
       program as an argument to hist then the value of the variable HISTEDIT is used.  If HISTE-
       DIT is unset, the obsolete variable FCEDIT is  used.   If  FCEDIT  is  not  defined,  then
       /bin/ed is used.  The edited command(s) is printed and re-executed upon leaving the editor
       unless you quit without writing.  The -s option (and in obsolete versions, the editor name
       -)  is  used to skip the editing phase and to re-execute the command.  In this case a sub-
       stitution parameter of the form old=new can be used to modify the  command  before  execu-
       tion.   For  example,  with  the  preset alias r, which is aliased to 'hist -s', typing `r
       bad=good c' will re-execute the most recent command which starts with the  letter  c,  re-
       placing the first occurrence of the string bad with the string good.

   In-line Editing Options.
       Normally,  each  command line entered from a terminal device is simply typed followed by a
       new-line (`RETURN' or `LINE FEED').  If either the emacs, gmacs, or vi option  is  active,
       the  user  can  edit the command line.  To be in either of these edit modes set the corre-
       sponding option.  An editing option is automatically selected each time the VISUAL or EDI-
       TOR variable is assigned a value ending in either of these option names.

       The  editing  features require that the user's terminal accept `RETURN' as carriage return
       without line feed and that a space (` ') must  overwrite  the  current  character  on  the
       screen.

       Unless the multiline option is on, the editing modes implement a concept where the user is
       looking through a window at the current line.  The window width is the value of COLUMNS if
       it  is  defined, otherwise 80.  If the window width is too small to display the prompt and
       leave at least 8 columns to enter input, the prompt is truncated from the  left.   If  the
       line is longer than the window width minus two, a mark is displayed at the end of the win-
       dow to notify the user.  As the cursor moves and reaches the window boundaries the  window
       will  be  centered  about  the  cursor.  The mark is a > (<, *) if the line extends on the
       right (left, both) side(s) of the window.

       The search commands in each edit mode provide access to the history  file.   Only  strings
       are matched, not patterns, although a leading ^ in the string restricts the match to begin
       at the first character in the line.

       Each of the edit modes has an operation to list the files or commands that  match  a  par-
       tially  entered word.  When applied to the first word on the line, or the first word after
       a ;, |, &, or (, and the word does not begin with ~ or contain a /, the list  of  aliases,
       functions,  and executable commands defined by the PATH variable that could match the par-
       tial word is displayed.  Otherwise, the list of files that match the given  word  is  dis-
       played.  If the partially entered word does not contain any file expansion characters, a *
       is appended before generating these lists.  After displaying the generated list, the input
       line  is redrawn.  These operations are called command name listing and file name listing,
       respectively.  There are additional operations, referred to as command name completion and
       file name completion, which compute the list of matching commands or files, but instead of
       printing the list, replace the current word with a complete or partial  match.   For  file
       name  completion, if the match is unique, a / is appended if the file is a directory and a
       space is appended if the file is not a directory.  Otherwise, the  longest  common  prefix
       for  all the matching files replaces the word.  For command name completion, only the por-
       tion of the file names after the last / are used to find the longest command  prefix.   If
       only  a  single  name matches this prefix, then the word is replaced with the command name
       followed by a space.  When using a tab for completion that does not yield a unique  match,
       a subsequent tab will provide a numbered list of matching alternatives.  A specific selec-
       tion can be made by entering the selection number followed by a tab.

   Key Bindings.
       The KEYBD trap can be used to intercept keys as they are typed and change  the  characters
       that  are  actually seen by the shell.  This trap is executed after each character (or se-
       quence of characters when the first character is ESC) is entered while reading from a ter-
       minal.   The variable .sh.edchar contains the character or character sequence which gener-
       ated the trap.  Changing the value of .sh.edchar in the trap action causes  the  shell  to
       behave as if the new value were entered from the keyboard rather than the original value.

       The  variable .sh.edcol is set to the input column number of the cursor at the time of the
       input.  The variable .sh.edmode is set to ESC when in vi insert mode (see  below)  and  is
       null  otherwise.   By prepending ${.sh.editmode} to a value assigned to .sh.edchar it will
       cause the shell to change to control mode if it is not already in this mode.

       This trap is not invoked for characters entered as arguments  to  editing  directives,  or
       while reading input for a character search.

   Emacs Editing Mode.
       This  mode  is  entered by enabling either the emacs or gmacs option.  The only difference
       between these two modes is the way they handle ^T.  To edit, the user moves the cursor  to
       the  point  needing  correction and then inserts or deletes characters or words as needed.
       All the editing commands are control characters or escape  sequences.   The  notation  for
       control  characters  is caret (^) followed by the character.  For example, ^F is the nota-
       tion for control F.  This is entered by depressing `f' while holding down the `CTRL' (con-
       trol)  key.   The  `SHIFT'  key  is  not  depressed.   (The notation ^?  indicates the DEL
       (delete) key.)

       The notation for escape sequences is M- followed by a character.  For example,  M-f  (pro-
       nounced  Meta  f) is entered by depressing ESC (ASCII 033) followed by `f'.  (M-F would be
       the notation for ESC followed by `SHIFT' (capital) `F'.)

       All edit commands operate from any place on the line (not just at the beginning).  Neither
       the `RETURN' nor the `LINE FEED' key is entered after edit commands except when noted.

       The M-[ multi-character commands below are DEC VT220 escape sequences generated by special
       keys on standard PC keyboards, such as the arrow keys.  You could type them  directly  but
       they are meant to recognize the keys in question, which are indicated in parentheses.

       ^F        Move cursor forward (right) one character.
       M-[C      (Right arrow) Same as ^F.
       M-f       Move cursor forward one word.  (The emacs editor's idea of a word is a string of
                 characters consisting of only letters, digits and underscores.)
       ^B        Move cursor backward (left) one character.
       M-[D      (Left arrow) Same as ^B.
       M-b       Move cursor backward one word.
       ^A        Move cursor to start of line.
       M-[H      (Home) Same as ^A.
       ^E        Move cursor to end of line.
       M-[F      (End) Same as ^E.
       M-[Y      Same as ^E.
       ^]char    Move cursor forward to character char on current line.
       M-^]char  Move cursor backward to character char on current line.
       ^X^X      Interchange the cursor and mark.
       erase     (User defined erase character as defined by the stty(1) command, usually  ^H  .)
                 Delete previous character.
       lnext     (User defined literal next character as defined by the stty(1) command, or ^V if
                 not defined.)  Removes the next character's editing features (if any).
       ^D        Delete current character.
       M-[3~     (Forward delete) Same as ^D.
       M-d       Delete current word.
       M-^H      (Meta-backspace) Delete previous word.
       M-h       Delete previous word.
       M-^?      (Meta-DEL) Delete previous word (if your interrupt character is  ^?   (DEL,  the
                 default) then this command will not work).
       ^T        Transpose  current  character  with previous character and advance the cursor in
                 emacs mode.  Transpose two previous characters in gmacs mode.
       ^C        Capitalize current character.
       M-c       Capitalize current word.
       M-l       Change the current word to lower case.
       ^K        Delete from the cursor to the end of the line.  If preceded by a  numerical  pa-
                 rameter  whose  value is less than the current cursor position, then delete from
                 given position up to the cursor.  If preceded by  a  numerical  parameter  whose
                 value is greater than the current cursor position, then delete from cursor up to
                 given cursor position.
       ^W        Kill from the cursor to the mark.
       M-p       Push the region from the cursor to the mark on the stack.
       kill      (User defined kill character as defined by the stty command, usually ^U .)  Kill
                 the  entire current line.  If two kill characters are entered in succession, all
                 kill characters from then on cause a line feed (useful when using  paper  termi-
                 nals).  A subsequent pair of kill characters undoes this change.
       ^Y        Restore last item removed from line. (Yank item back to the line.)
       ^L        Line feed and print current line.
       M-^L      Clear the screen.
       ^@        (Null character) Set mark.
       M-space   (Meta space) Set mark.
       ^J        (New line) Execute the current line.
       ^M        (Return) Execute the current line.
       eof       End-of-file  character,  normally ^D, is processed as an End-of-file only if the
                 current line is null.
       ^P        Fetch previous command.  Each time ^P is entered the previous  command  back  in
                 time  is  accessed.   Moves back one line when not on the first line of a multi-
                 line command.
       M-[A      (Up arrow) If the cursor is at the end of the line, it is equivalent to ^R  with
                 string  set to the contents of the current line.  Otherwise, it is equivalent to
                 ^P.
       M-<       Fetch the least recent (oldest) history line.
       M->       Fetch the most recent (youngest) history line.
       ^N        Fetch next command line.  Each time ^N is entered the next command line  forward
                 in time is accessed.
       M-[B      (Down arrow) Equivalent to ^N.
       ^Rstring  Reverse  search history for a previous command line containing string.  If a pa-
                 rameter of zero is given, the search is forward.  String is terminated by a `RE-
                 TURN'  or `NEW LINE'.  If string is preceded by a ^, the matched line must begin
                 with string.  If string is omitted, then the next command  line  containing  the
                 most  recent  string is accessed.  In this case a parameter of zero reverses the
                 direction of the search.
       ^O        Operate - Execute the current line and fetch the next line relative  to  current
                 line from the history file.
       M-digits  (Escape)  Define  numeric  parameter, the digits are taken as a parameter to the
                 next command.  The commands that accept a parameter are ^F, ^B, erase,  ^C,  ^D,
                 ^K, ^R, ^P, ^N, ^], M-., M-^], M-_, M-=, M-b, M-c, M-d, M-f, M-h, M-l, M-^H, and
                 the arrow keys and forward-delete key.
       M-letter  Soft-key - Your alias list is searched for an alias by the name _letter  and  if
                 an alias of this name is defined, its value will be inserted on the input queue.
                 The letter must not be one of the above meta-functions.
       M-[letter Soft-key - Your alias list is searched for an alias by the name __letter and  if
                 an alias of this name is defined, its value will be inserted on the input queue.
                 This can be used to program function keys on many terminals.
       M-.       The last word of the previous command is inserted on the line.  If preceded by a
                 numeric  parameter,  the value of this parameter determines which word to insert
                 rather than the last word.
       M-_       Same as M-..
       M-*       Attempt pathname expansion on the current word.  An asterisk is appended if  the
                 word doesn't match any file or contain any special pattern characters.
       M-ESC     Command or file name completion as described above.
       ^I tab    Attempts  command or file name completion as described above.  If a partial com-
                 pletion occurs, repeating this will behave as if M-= were entered.  If no  match
                 is found or entered after space, a tab is inserted.
       M-=       If  not  preceded by a numeric parameter, it generates the list of matching com-
                 mands or file names as described above.  Otherwise, the word under the cursor is
                 replaced  by  the  item corresponding to the value of the numeric parameter from
                 the most recently generated command or file list.  If the cursor  is  not  on  a
                 word, it is inserted instead.
       ^U        Multiply parameter of next command by 4.
       \         If the backslashctrl shell option is on (which is the default setting), this es-
                 capes the next character.  Editing characters, the user's erase, kill and inter-
                 rupt  (normally  ^C)  characters may be entered in a command line or in a search
                 string if preceded by a \.  The \ removes the next character's editing  features
                 (if any).  See also lnext which is not subject to any shell option.
       M-^V      Display version of the shell.
       M-#       If  the  line  does  not begin with a #, a # is inserted at the beginning of the
                 line and after each new-line, and the line is entered.  This causes a comment to
                 be  inserted in the history file.  If the line begins with a #, the # is deleted
                 and one # after each new-line is also deleted.

   Vi Editing Mode.
       There are two typing modes.  Initially, when you enter a command  you  are  in  the  input
       mode.   To  edit, the user enters control mode by typing ESC (033) and moves the cursor to
       the point needing correction and then inserts or deletes characters or  words  as  needed.
       Most control commands accept an optional repeat count prior to the command.

       The notation for control characters used below is ^ followed by a character. For instance,
       ^H is entered by holding down the Control key and pressing H.  ^[ (Control+[)  is  equiva-
       lent  to  the  ESC  key.   The notation for escape sequences is ^[ followed by one or more
       characters.

       The ^[[ (ESC [) multi-character commands below are DEC VT220 escape sequences generated by
       special  keys  on  standard  PC  keyboards, such as the arrow keys, which are indicated in
       parentheses. When in input mode, these keys will switch you to control  mode  before  per-
       forming the associated action.  These sequences can use preceding repeat count parameters,
       but only when the ^[ and the subsequent [ are entered into the input buffer  at  the  same
       time, such as when pressing one of those keys.

        Input Edit Commands
              By default the editor is in input mode.
              erase     (User  defined erase character as defined by the stty command, usually ^H
                        or #.)  Delete previous character.
              ^W        Delete the previous blank separated word.  On some systems the viraw  op-
                        tion may be required for this to work.
              eof       As  the  first character of the line causes the shell to terminate unless
                        the ignoreeof option is set.  Otherwise this character is ignored.
              lnext     (User defined literal next character as defined by the stty(1) or  ^V  if
                        not  defined.)   Removes  the next character's editing features (if any).
                        On some systems the viraw option may be required for this to work.
              \         If the backslashctrl shell option is on (which is the  default  setting),
                        this escapes the next erase or kill character.
              ^I tab    Attempts  command  or file name completion as described above and returns
                        to input mode.  If a partial completion occurs, repeating this  will  be-
                        have as if = were entered from control mode.  If no match is found or en-
                        tered after space, a tab is inserted.
        Motion Edit Commands
              These commands will move the cursor.
              [count]l  Cursor forward (right) one character.
              [count]^[[C
                        (Right arrow) Same as l.
              [count]w  Cursor forward one alphanumeric word.
              [count]W  Cursor to the beginning of the next word that follows a blank.
              [count]e  Cursor to end of word.
              [count]E  Cursor to end of the current blank delimited word.
              [count]h  Cursor backward (left) one character.
              [count]^[[D
                        (Left arrow) Same as h.
              [count]b  Cursor backward one word.
              [count]B  Cursor to preceding blank separated word.
              [count]|  Cursor to column count.
              [count]fc Find the next character c in the current line.
              [count]Fc Find the previous character c in the current line.
              [count]tc Equivalent to f followed by h.
              [count]Tc Equivalent to F followed by l.
              [count];  Repeats count times, the last single character find command, f, F, t,  or
                        T.
              [count],  Reverses the last single character find command count times.
              0         Cursor to start of line.
              ^[[H      (Home) Same as 0.
              ^         Cursor to first non-blank character in line.
              $         Cursor to end of line.
              ^[[F      (End) Same as $.
              ^[[Y      Same as $.
              %         Moves  to  balancing (, ), {, }, [, or ].  If cursor is not on one of the
                        above characters, the remainder of the line is searched for the first oc-
                        currence of one of the above characters first.
        Search Edit Commands
              These commands access your command history.
              [count]k  Fetch previous command.  Each time k is entered the previous command back
                        in time is accessed.
              [count]-  Equivalent to k.
              [count]^[[A
                        (Up arrow) If cursor is at the end of the line it is equivalent to / with
                        string set to the contents of the current line.  Otherwise, it is equiva-
                        lent to k.
              [count]j  Fetch next command.  Each time j is entered the next command  forward  in
                        time is accessed.
              [count]+  Equivalent to j.
              [count]^[[B
                        (Down arrow) Equivalent to j.
              [count]G  The  command  number  count  is fetched.  The default is the least recent
                        history command.
              /string   Search backward through history for a previous command containing string.
                        String  is terminated by a `RETURN' or `NEW LINE'.  If string is preceded
                        by a ^, the matched line must begin with string.  If string is null,  the
                        previous string will be used.
              ?string   Same as / except that search will be in the forward direction.
              n         Search for next match of the last pattern to / or ?  commands.
              N         Search  for  next match of the last pattern to / or ?, but in reverse di-
                        rection.
        Text Modification Edit Commands
              These commands will modify the line.
              a         Enter input mode and enter text after the current character.
              A         Append text to the end of the line.  Equivalent to $a.
              [count]cmotion
              c[count]motion
                        Delete current character through the character that motion would move the
                        cursor  to and enter input mode.  If motion is c, the entire line will be
                        deleted and input mode entered.
              C         Delete the current character through the end  of  line  and  enter  input
                        mode.  Equivalent to c$.
              S         Equivalent to cc.
              [count]s  Replace characters under the cursor in input mode.
              D         Delete the current character through the end of line.  Equivalent to d$.
              [count]dmotion
              d[count]motion
                        Delete current character through the character that motion would move to.
                        If motion is d , the entire line will be deleted.
              i         Enter input mode and insert text before the current character.
              I         Insert text before the beginning of the line.  Equivalent to 0i.
              [count]P  Place the previous text modification before the cursor.
              [count]p  Place the previous text modification after the cursor.
              R         Enter input mode and replace characters on the screen with characters you
                        type overlay fashion.
              [count]rc Replace  the  count  character(s) starting at the current cursor position
                        with c, and advance the cursor.
              [count]x  Delete current character.
              [count]^[[3~
                        (Forward delete) Same as x.
              [count]X  Delete preceding character.
              [count].  Repeat the previous text modification command.
              [count]~  Invert the case of the count character(s) starting at the current  cursor
                        position and advance the cursor.
              [count]_  Causes  the  count  word of the previous command to be appended and input
                        mode entered.  The last word is used if count is omitted.
              *         Causes an * to be appended to the current word and pathname expansion at-
                        tempted.   If  no match is found, it rings the bell.  Otherwise, the word
                        is replaced by the matching pattern and input mode is entered.
              \         Command or file name completion as described above.
        Other Edit Commands
              Miscellaneous commands.
              [count]ymotion
              y[count]motion
                        Yank current character through character that motion would move the  cur-
                        sor to and puts them into the delete buffer.  The text and cursor are un-
                        changed.
              yy        Yanks the entire line.
              Y         Yanks from current position to end of line.  Equivalent to y$.
              u         Undo the last text modifying command.
              U         Undo all the text modifying commands performed on the line.
              [count]v  Returns the command hist -e ${VISUAL:-${EDITOR:-vi}} count in  the  input
                        buffer.  If count is omitted, then the current line is used.
              ^L        Line feed and print current line.  Has effect only in control mode.
              ^J        (New line) Execute the current line, regardless of mode.
              ^M        (Return) Execute the current line, regardless of mode.
              #         If  the  first character of the command is a #, then this command deletes
                        this # and each # that follows a newline.  Otherwise, sends the line  af-
                        ter inserting a # in front of each line in the command.  Useful for caus-
                        ing the current line to be inserted in the history as a comment  and  un-
                        commenting previously commented commands in the history file.
              [count]=  If  count is not specified, it generates the list of matching commands or
                        file names as described above.  Otherwise, the word under the  cursor  is
                        replaced  by  the  count item from the most recently generated command or
                        file list.  If the cursor is not on a word, it is inserted instead.
              @letter   Your alias list is searched for an alias by the name _letter  and  if  an
                        alias  of  this  name is defined, its value will be inserted on the input
                        queue for processing.
              ^V        Display version of the shell.

   Built-in Commands.
       The simple-commands listed below are built in to the shell and are executed  in  the  same
       process as the shell.  The effects of any added Input/Output redirections are local to the
       command, except for the exec and redirect commands.  Unless otherwise indicated, the  out-
       put  is  written on standard output (file descriptor 1) and the exit status, when there is
       no syntax error, is zero.  Except for :, true, false, and echo, all built-in commands  ac-
       cept -- to indicate end of options, and are self-documenting.

       The self-documenting commands interpret the option --man as a request to display that com-
       mand's own manual page, --help as a request to display the OPTIONS section from their man-
       ual page, and -?  as a request to print a brief usage message.  All these are processed as
       error messages, so they are written on standard error (file descriptor 2) and to pipe them
       into  a pager such as more(1) you need to add a 2>&1 redirection before the |. The display
       of boldface text depends on whether standard error is on a terminal, so is  disabled  when
       using  a  pager.  Exporting the ERROR_OPTIONS environment variable with a value containing
       emphasis will force this on; a value containing noemphasis forces it off.  The test/[ com-
       mand  needs  an  additional -- argument to recognize self-documentation options, e.g. test
       --man --.  The exec and redirect commands, as they make redirections permanent, should use
       self-documentation  options  in a subshell when redirecting, for example: (redirect --man)
       2>&1.  There are advanced output options as well; see getopts --man for more information.

       Commands that are preceded by a <*> symbol below  are  special built-in commands  and  are
       treated specially in the following ways:
       1.     Variable  assignment  lists preceding the command remain in effect when the command
              completes.
       2.     I/O redirections are processed after variable assignments.
       3.     Errors cause a script that contains them to abort.
       4.     They are not valid function names.
       Commands that are preceded by a <**> symbol below are declaration commands.  Any following
       words  that are in the format of a variable assignment are expanded with the same rules as
       a variable assignment.  This means that tilde expansion is performed after the = sign, ar-
       ray  assignments  of the form varname=(assign_list) are supported, and field splitting and
       pathname expansion are not performed.

       <*> : [ arg ... ]
              The command only expands parameters.

       <*> . name [ arg ... ]
              If name is a function defined with the function  name  reserved  word  syntax,  the
              function is executed in the current environment (as if it had been defined with the
              name() syntax).  Otherwise if name refers to a file, the file is read  in  its  en-
              tirety  and the commands are executed in the current shell environment.  The search
              path specified by PATH is used to find the directory containing the file.   If  any
              arguments arg are given, they become the positional parameters while processing the
              .  command and the original positional parameters  are  restored  upon  completion.
              Otherwise  the  positional  parameters  are unchanged.  The exit status is the exit
              status of the last command executed.

       [ expression ]
              The [ command is the same as test, with the exception that an additional closing  ]
              argument is required. See test below.

       alias [ -ptx ]  [ name[ =value  ] ] ...
              alias  with no arguments prints the list of aliases in the form name=value on stan-
              dard output.  The -p option causes the word alias to be inserted before  each  one.
              When one or more arguments are given, an alias is defined for each name whose value
              is given.  A trailing space in value causes the next word to be checked  for  alias
              substitution.  With the -t option, each name is looked up as a command in $PATH and
              its path is added to the hash table as a 'tracked alias'.  If  no  name  is  given,
              this  prints the hash table. See hash.  Without the -t option, for each name in the
              argument list for which no value is given, the name  and  value  of  the  alias  is
              printed.   The  obsolete -x option has no effect.  The exit status is non-zero if a
              name is given, but no value, and no alias has been defined for the name.

       autoload name ...
              Marks each name undefined so that the FPATH variable will be searched to  find  the
              function definition when the function is referenced.  The same as typeset -fu.

       bg [ job... ]
              This  command is only on systems that support job control.  Puts each specified job
              into the background.  The current job is put in the background if job is not speci-
              fied.  See Jobs for a description of the format of job.

       <*> break [ n ]
              Exit  from the enclosing for, while, until, or select loop, if any.  If n is speci-
              fied, then break n levels.

       builtin [ -ds ] [ -f file ] [ name ... ]
              If name is not specified, and no -f option is specified, the built-ins are  printed
              on  standard  output.  The -s option prints only the special built-ins.  Otherwise,
              each name represents the pathname whose basename is the name of the built-in.   The
              entry  point  function name is determined by prepending b_ to the built-in name.  A
              built-in specified by a pathname will only be executed when that pathname would  be
              found  during  the path search.  Built-ins found in libraries loaded via the .paths
              file will associate with the pathname of the directory containing the .paths file.

              The ISO C/C++ prototype is b_mycommand(int argc, char *argv[], void  *context)  for
              the  builtin  command mycommand where argv is array an of argc elements and context
              is an optional pointer to a Shell_t structure as described in <ast/shell.h>.

              Special built-ins cannot be bound to a pathname or deleted.  The -d option  deletes
              each  of  the given built-ins.  On systems that support dynamic loading, the -f op-
              tion names a shared library containing the code for built-ins.  The shared  library
              prefix  and/or  suffix, which depend on the system, can be omitted.  Once a library
              is loaded, its symbols become available  for  subsequent  invocations  of  builtin.
              Multiple  libraries  can be specified with separate invocations of the builtin com-
              mand.  Libraries are searched in the reverse order in  which  they  are  specified.
              When  a  library  is  loaded,  it looks for a function in the library whose name is
              lib_init() and invokes this function with an argument of 0.

       cd [ -L ] [ -eP ] [ arg ]
       cd [ -L ] [ -eP ] old new
              This command can be in either of two forms.  In the first form it changes the  cur-
              rent directory to arg.  If arg is - the directory is changed to the previous direc-
              tory.  The shell variable HOME is the default arg.  The variable PWD is set to  the
              current  directory.   The shell variable CDPATH defines the search path for the di-
              rectory containing arg.  Alternative directory names are separated by a colon  (:).
              The  default path is <null> (specifying the current directory).  Note that the cur-
              rent directory is specified by a null path name, which can appear immediately after
              the  equal sign or between the colon delimiters anywhere else in the path list.  If
              arg begins with a / then the search path is not used.  Otherwise, each directory in
              the path is searched for arg.
              The  second form of cd substitutes the string new for the string old in the current
              directory name, PWD, and tries to change to this new directory.
              By default, symbolic link names are treated literally when  finding  the  directory
              name.  This is equivalent to the -L option.  The -P option causes symbolic links to
              be resolved when determining the directory.  The last instance of -L or -P  on  the
              command line determines which method is used.
              If  -e  and -P are both in effect and the correct PWD could not be determined after
              successfully changing the directory, cd will return with exit status one  and  pro-
              duce  no  output.   If any other error occurs while both flags are active, the exit
              status is greater than one.
              The cd command may not be executed by rksh.

       command [ -pvxV ] name [ arg ... ]
              With the -v option, command is equivalent to the built-in whence command  described
              below.  The -V option causes command to act like whence -v.

              Without  the  -v  or  -V options, command executes name with the arguments given by
              arg.  Functions and aliases will not be searched for when finding  name.   If  name
              refers  to  a special built-in, as marked with <*> in this manual, command disables
              the special properties described above for that mark, executing the  command  as  a
              regular built-in.  (For example, using command set -o option-name prevents a script
              from terminating when an invalid option name is given.)

              The -p option causes the operating system's standard utilities path (as  output  by
              getconf PATH) to be searched rather than the one defined by the value of PATH.

              The  -x option runs name as an external command, bypassing built-ins.  If the argu-
              ments contain at least one word that expands to multiple arguments, such as "$@" or
              *.txt,  then  the  -x  option also allows executing external commands with argument
              lists that are longer than the operating system allows. This functionality is simi-
              lar  to xargs(1) but is easier to use. The shell does this by invoking the external
              command multiple times if needed, dividing the expanded argument list over the  in-
              vocations.  Any  arguments that come before the first word that expands to multiple
              arguments, as well as any that follow the last such word, are considered static ar-
              guments  and  are  repeated for each invocation. This allows each invocation to use
              the same command options, as well as the same trailing  destination  arguments  for
              commands like cp(1) or mv(1).  When all invocations are completed, command -x exits
              with the status of the invocation that had the highest  exit  status.   (Note  that
              command  -x may still fail with an "argument list too long" error if a single argu-
              ment exceeds the maximum length of the argument list, or if a long  arguments  list
              contains no word that expands to multiple arguments.)

       <**> compound vname[=value] ...
              Causes each vname to be a compound variable.  The same as typeset -C.

       <*> continue [ n ]
              Resume the next iteration of the enclosing for, while, until, or select loop.  If n
              is specified, then resume at the n-th enclosing loop.

       disown [ job... ]
              Causes the shell not to send a HUP signal to each given job, or all active jobs  if
              job is omitted, when a login shell terminates.

       echo [ arg ... ]
              When  the first arg does not begin with a -, and none of the arguments contain a \,
              then echo prints each of its arguments separated by a space  and  terminated  by  a
              new-line.   Otherwise, the behavior of echo is system dependent and print or printf
              described below should be used.  See echo(1) for usage and description.

       <**> enum [ -i  ] type[=(value ...) ]
              Creates a declaration command named type that allows one of the specified values as
              enumeration  names.  If =(value ...) is omitted, then type must be an indexed array
              variable with at least two elements and the values are taken from this array  vari-
              able.   If  -i  is specified the values are case-insensitive.  Declaration commands
              are created as special builtins that cannot be removed or overridden by shell func-
              tions.   Each  created declaration command has a --man option that shows documenta-
              tion on its type's behavior and possible values.

              Within arithmetic expressions (see Arithmetic Evaluation above),  enumeration  type
              values  translate to index numbers between 0 and the number of defined values minus
              1. It is an error for an arithmetic expression to assign a value  outside  of  that
              range. Decimal fractions are ignored.

       <*> eval [ arg ... ]
              The arguments are read as input to the shell and the resulting command(s) executed.

       <*> exec [ -c ] [ -a name ] [ arg ... ]
              If  arg  is  given,  the command specified by the arguments is executed in place of
              this shell without creating a new process.  The  value  of  the  SHLVL  environment
              variable  is decreased by one, unless the shell replaced is a subshell.  The -c op-
              tion causes the environment to be cleared before applying variable assignments  as-
              sociated with the exec invocation.  The -a option causes name rather than the first
              arg, to become argv[0] for the new process.  If arg is not given and only I/O redi-
              rections  are given, then this command persistently modifies file descriptors as in
              redirect.

       <*> exit [ n ]
              Causes the shell to exit with the exit status specified by n.  The  value  will  be
              the  least significant 8 bits of n (if specified) or of the exit status of the last
              command executed.  An end-of-file will also cause the shell to exit, except for  an
              interactive shell that has the ignoreeof option turned on (see set below).

       <*><**> export [ -p ] [ name[=value] ] ...
              If  name is not given, the names and values of each variable with the export attri-
              bute are printed with the values quoted in a manner that allows them to  be  re-in-
              put.   The  export  command is the same as typeset -x except that if you use export
              within a function, no local variable is created.  The -p option causes the word ex-
              port to be inserted before each one.  Otherwise, the given names are marked for au-
              tomatic export to the environment of subsequently-executed commands.

       false  Does nothing, and exits 1. Used with until for infinite loops.

       fc [ -e ename  ] [ -N num ] [ -nlr ] [ first [ last ] ]
       fc -s  [ old=new ] [ command ]
              The same as hist.

       fg [ job... ]
              This command is only on systems that support job control.  Each  job  specified  is
              brought  to  the  foreground and waited for in the specified order.  Otherwise, the
              current job is brought into the foreground.  See Jobs for a description of the for-
              mat of job.

       <**> float vname[=value] ...
              Declares each vname to be a long floating point number.  The same as typeset -lE.

       functions [ -Stux ] [ name ... ]
              Lists functions.  The same as typeset -f.

       getconf [ name [ pathname ] ]
              Prints the current value of the configuration parameter given by name.  The config-
              uration parameters are defined by the IEEE POSIX 1003.1 and IEEE POSIX 1003.2 stan-
              dards.   (See  pathconf(2)  and sysconf(3).)  The pathname argument is required for
              parameters whose value depends on the location in the file system.  If no arguments
              are given, getconf prints the names and values of the current configuration parame-
              ters.  The pathname / is used for each of the parameters that requires pathname.

       getopts [ -a name ] optstring vname [ arg ... ]
              Checks arg for legal options.  If arg is omitted,  the  positional  parameters  are
              used.   An  option argument begins with a + or a -.  An option not beginning with +
              or - or the argument -- ends the options.  Options beginning with + are only recog-
              nized  when optstring begins with a +.  optstring contains the letters that getopts
              recognizes.  If a letter is followed by a :, that option is expected to have an ar-
              gument.   The  options can be separated from the argument by blanks.  The option -?
              causes getopts to generate a usage message on standard error.  The -a argument  can
              be used to specify the name to use for the usage message, which defaults to $0.
              getopts  places  the next option letter it finds inside variable vname each time it
              is invoked.  The option letter will be prepended with a + when arg begins with a +.
              The  index  of the next arg is stored in OPTIND.  The option argument, if any, gets
              stored in OPTARG.
              A leading : in optstring causes getopts to store the letter of an invalid option in
              OPTARG,  and  to set vname to ?  for an unknown option and to : when a required op-
              tion argument is missing.  Otherwise, getopts prints an error  message.   The  exit
              status is non-zero when there are no more options.
              There  is  no way to specify any of the options :, +, -, ?, [, and ].  The option #
              can only be specified as the first option.

       hash [ -r ] [ utility ]
              hash displays or modifies the hash table with the locations of recently  used  pro-
              grams.  If  given  no  arguments,  it  lists  all command/path associations (a.k.a.
              'tracked aliases') in the hash table. Otherwise, hash performs a  PATH  search  for
              each utility supplied and adds the result to the hash table.  The -r option empties
              the hash table. This can also be achieved by resetting PATH.

       hist [ -e ename  ] [ -N num ] [ -nlr ] [ first [ last ] ]
       hist -s [ old=new ] [ command ]
              In the first form, a range of commands from first to last is selected from the last
              HISTSIZE  commands  that  were typed at the terminal.  The arguments first and last
              may be specified as a number or as a string.  A string is used to locate  the  most
              recent  command  starting  with  the given string.  A negative number is used as an
              offset to the current command number.  If the -l option is selected,  the  commands
              are listed on standard output.  Otherwise, the editor program ename is invoked on a
              file containing these keyboard commands.  If ename is not supplied, then the  value
              of  the  variable  HISTEDIT  is used.  If HISTEDIT is not set, then FCEDIT (default
              /bin/ed) is used as the editor.  When editing is complete, the edited command(s) is
              executed if the changes have been saved.  If last is not specified, then it will be
              set to first.  If first is not specified, the default is the previous  command  for
              editing  and -16 for listing.  The option -r reverses the order of the commands and
              the option -n suppresses command numbers when listing.  In the second form, command
              is  interpreted as first described above and defaults to the last command executed.
              The resulting command is executed after the optional substitution old=new  is  per-
              formed.  The option -N causes hist to start num commands back.

       <**> integer vname[=value] ...
              Declares each vname to be a long integer number.  The same as typeset -li.

       jobs [ -lnp ] [ job ... ]
              Lists  information about each given job; or all active jobs if job is omitted.  The
              -l option lists process ids in addition to the normal information.  The  -n  option
              only  displays jobs that have stopped or exited since last notified.  The -p option
              causes only the process group to be listed.  See Jobs for a description of the for-
              mat of job.

       kill [ -s signame ] job ...
       kill [ -n signum ] job ...
       kill -Ll [ sig ... ]
              Sends  either  the TERM (terminate) signal or the specified signal to the specified
              jobs or processes.  Signals are either given by number with the  -n  option  or  by
              name  with  the  -s  option (as given in <signal.h>, stripped of the prefix ``SIG''
              with the exception that SIGCLD is named CHLD).  For backward compatibility,  the  n
              and s can be omitted and the number or name placed immediately after the -.  If the
              signal being sent is TERM (terminate) or HUP (hangup), then the job or process will
              be  sent  a  CONT  (continue) signal if it is stopped.  The argument job can be the
              process id of a process that is not a member of one of the active jobs.   See  Jobs
              for a description of the format of job.  In the third form, kill -l, or kill -L, if
              sig is not specified, the signal names are listed.  The -l  option  list  only  the
              signal  names.  -L options lists each signal name and corresponding number.  Other-
              wise, for each sig that is a name, the corresponding signal number is listed.   For
              each sig that is a number, the signal name corresponding to the least significant 8
              bits of sig is listed.

       let arg ...
              Each arg is a separate arithmetic expression to be evaluated.  let only  recognizes
              octal  numbers  starting with 0 when the set option letoctal is on.  See Arithmetic
              Evaluation above for a description of arithmetic expression evaluation.
              The exit status is 0 if the value of the last expression is non-zero, and 1  other-
              wise.

       <**> nameref vname[=refname] ...
              Declares each vname to be a variable name reference.  The same as typeset -n.

       print [ -CRenprsv ] [ -u unit ] [ -f format ] [ arg ... ]
              With  no  options  or  with option - or --, each arg is printed on standard output.
              The -f option causes the arguments to be printed as described by printf.   In  this
              case,  any e, n, r, R options are ignored.  Otherwise, unless the -C, -R, -r, or -v
              are specified, the following escape conventions will be applied:
              \a     The alert character (ASCII 07).
              \b     The backspace character (ASCII 010).
              \c     Causes print to end without processing more arguments and not adding a  new-
                     line.
              \f     The formfeed character (ASCII 014).
              \n     The newline character (ASCII 012).
              \r     The carriage return character (ASCII 015).
              \t     The tab character (ASCII 011).
              \v     The vertical tab character (ASCII 013).
              \E     The escape character (ASCII 033).
              \\     The backslash character \.
              \0x    The character defined by the 1, 2, or 3-digit octal string given by x.

              The  -R  option will print all subsequent arguments and options other than -n.  The
              -e causes the above escape conventions to be applied.  This is the  default  behav-
              ior.   It reverses the effect of an earlier -r.  The -p option causes the arguments
              to be written onto the pipe of the process spawned with |& instead of standard out-
              put.   The -v option treats each arg as a variable name and writes the value in the
              printf %B format.  The -C option treats each arg as a variable name and writes  the
              value  in  the printf %#B format.  The -s option causes the arguments to be written
              onto the history file instead of standard output.  The -u option  can  be  used  to
              specify  a  one  digit file descriptor unit number unit on which the output will be
              placed.  The default is 1.  If the option -n is used, no new-line is added  to  the
              output.

       printf [ -v vname ] format [ arg ... ]
              The arguments arg are printed on standard output in accordance with the ANSI C for-
              matting rules associated with the format string format.  If the number of arguments
              exceeds  the number of format specifications, the format string is reused to format
              remaining arguments.  The following extensions can also be used:
              %b     A %b format can be used instead of %s to cause escape sequences in the  cor-
                     responding arg to be expanded as described in print.
              %B     A %B option causes each of the arguments to be treated as variable names and
                     the binary value of variable will be printed.  The alternate flag # causes a
                     compound  variable  to  be output on a single line.  This is most useful for
                     compound variables and variables whose attribute is -b.
              %H     A %H format can be used instead of %s to cause characters in  arg  that  are
                     special  in  HTML  and XML to be output as their entity name.  The alternate
                     flag # formats the output for use as a URI.
              %p     A %p format will convert the given number to hexadecimal.
              %P     A %P format can be used instead of %s to cause arg to be interpreted  as  an
                     extended regular expression and be printed as a shell pattern.
              %q     A  %q  format  can be used instead of %s to cause the resulting string to be
                     quoted in a manner than can be reinput to the shell.  When q is preceded  by
                     the alternative format specifier, #, the string is quoted in manner suitable
                     as a field in a .csv format file.
              %(date-format)T
                     A %(date-format)T format can be used to treat an  argument  as  a  date/time
                     string and to format the date/time according to the date-format.
              %Q     A %Q format will convert the given number of seconds to readable time.
              %R     A  %R  format  can be used instead of %s to cause arg to be interpreted as a
                     shell pattern and to be printed as an extended regular expression.
              %Z     A %Z format will output a byte whose value is 0.
              %d     The precision field of the %d format can be followed by a .  and the  output
                     base.  In this case, the # flag character causes base# to be prepended.
              #      The  #  flag,  when used with the %d format without an output base, displays
                     the output in powers of 1000 indicated by one of the following suffixes: k M
                     G  T  P E, and when used with the %i format displays the output in powers of
                     1024 indicated by one of the following suffixes: Ki Mi Gi Ti Pi Ei.
              =      The = flag centers the output within the specified field width.
              L      The L flag, when used with the %c or %s formats, treats precision as charac-
                     ter width instead of byte count.
              ,      The  , flag, when used with the %d or %f formats, separates groups of digits
                     with the grouping delimiter (, on groups of 3 in the C locale).

              The -v option assigns the output directly to a variable instead of
                     writing it to standard output. This is faster than capturing the output  us-
                     ing  a command substitution and avoids the latter's stripping of final line-
                     feed characters (\n). The vname argument should be a  valid  variable  name,
                     optionally  with one or more array subscripts in square brackets.  Note that
                     square brackets should be quoted to avoid pathname expansion.

       pwd [ -LP ]
              Outputs the value of the current working directory.  The -L option is the  default;
              it  prints  the  logical name of the current directory.  If the -P option is given,
              all symbolic links are resolved from the name.  The last instance of -L  or  -P  on
              the command line determines which method is used.

       read  [  -ACSprsv  ]  [  -d  delim  ]  [  -n  n  ] [ [ -N n ] [ -t timeout ] [ -u unit ] [
       vname?prompt ] [ vname ... ]
              The shell input mechanism.  One line is read and is broken up into fields using the
              characters  in  IFS  as separators.  The escape character, \, is used to remove any
              special meaning for the next character and for line continuation.   The  -d  option
              causes  the  read to continue to the first character of delim rather than new-line.
              The -n option causes at most n bytes to read rather a full  line  but  will  return
              when  reading  from a slow device as soon as any characters have been read.  The -N
              option causes exactly n to be read unless an end-of-file has  been  encountered  or
              the  read  times out because of the -t option.  In raw mode, -r, the \ character is
              not treated specially.  The first field is assigned to the first vname, the  second
              field  to  the second vname, etc., with leftover fields assigned to the last vname.
              When vname has the binary attribute and -n or -N is specified, the bytes  that  are
              read are stored directly into the variable.  If the -v is specified, then the value
              of the first vname will be used as a default value when reading from a terminal de-
              vice.   The  -A option causes the variable vname to be unset and each field that is
              read to be stored in successive elements of the indexed array vname.  The -C option
              causes  the  variable  vname to be read as a compound variable.  Blanks will be ig-
              nored when finding the beginning open parenthesis.  The -S option causes  the  line
              to be treated like a record in a .csv format file so that double quotes can be used
              to allow the delimiter character and the new-line  character  to  appear  within  a
              field.   The  -p  option causes the input line to be taken from the input pipe of a
              process spawned by the shell using |&.  If the -s option is present, the input will
              be  saved as a command in the history file.  The option -u can be used to specify a
              one digit file descriptor unit unit to read  from.   The  file  descriptor  can  be
              opened  with  the exec special built-in command.  The default value of unit n is 0.
              The option -t is used to specify a timeout in seconds when reading from a  terminal
              or pipe.  If vname is omitted, then REPLY is used as the default vname.  An end-of-
              file with the -p option causes cleanup for this process  so  that  another  can  be
              spawned.  If the first argument contains a ?, the remainder of this word is used as
              a prompt on standard error when the shell is interactive.  The exit status is 0 un-
              less an end-of-file is encountered or read has timed out.

       <*><**> readonly [ -p ] [ vname[=value] ] ...
              If vname is not given, the names and values of each variable with the read-only at-
              tribute is printed with the values quoted in a manner that allows them to be re-in-
              put.   The -p option causes the word readonly to be inserted before each one.  Oth-
              erwise, the given vnames are marked read-only and these names cannot be changed  by
              subsequent assignment.  Unlike typeset -r , readonly does not create a function-lo-
              cal scope and the given vnames are marked  globally  read-only  by  default.   When
              defining  a type, if the value of a read-only subvariable is not defined, the value
              is required when creating each instance.

       redirect
              This command only accepts input/output redirections.  It can open and  close  files
              and  modify file descriptors from 0 to 9 as specified by the input/output redirect-
              ion list (see the Input/Output section above), with the difference that the  effect
              persists  past  the  execution of the redirect command.  When invoking another pro-
              gram, file descriptors greater than 2 that were opened with this mechanism are only
              passed on if they are explicitly redirected to themselves as part of the invocation
              (e.g. 4>&4) or if the posix option is set.

       <*> return [ n ]
              Causes a shell function, dot script (see . and source), or profile script to return
              to the invoking shell environment with the exit status specified by n.  This status
              value can use the full signed integer  range  as  shown  by  the  commands  getconf
              INT_MIN  and getconf INT_MAX. A value outside that range will produce a warning and
              an exit status of 128.  If n is omitted, then the value of $? is assumed, i.e., the
              exit  status of the last command executed is passed on.  If return is invoked while
              not in a function, dot script, or profile script, then it behaves the same as exit.

       <*> set [ +-BCGHabefhkmnprstuvx ] [ +-o [ option ] ] ... [ +-A vname ]  [ arg ... ]
              The options for this command have meaning as follows:
              -A      Array assignment.  Unset the variable vname and assign values  sequentially
                      from the arg list.  If +A is used, the variable vname is not unset first.
              -B      Enable brace group expansion. On by default, except if ksh is invoked as sh
                      or rsh.
              -C      Prevents redirection > from truncating existing files.  Files that are cre-
                      ated  are opened with the O_EXCL mode.  Requires >| to truncate a file when
                      turned on.
              -G      Enables recursive pathname expansion.  This adds the double-star pattern **
                      to  the  pathname  expansion (see Pathname Expansion above).  By itself, it
                      matches the recursive contents of the current directory, which is  to  say,
                      all files and directories in the current directory and in all its subdirec-
                      tories, sub-subdirectories, and so on.  If the  pathname  pattern  ends  in
                      **/,  only  directories  and subdirectories are matched, including symbolic
                      links that point to directories.  A prefixed directory name is not included
                      in the results unless that directory was itself found by a pattern. For ex-
                      ample, dir/** matches the recursive contents of dir  but  not  dir  itself,
                      whereas di[r]/** matches both dir itself and the recursive contents of dir.
                      Symbolic links to non-directories are not followed.  Symbolic links to  di-
                      rectories  are  followed if they are specified literally or match a pattern
                      as described under Pathname Expansion, but not if they result from  a  dou-
                      ble-star pattern.
              -H      Enable !-style history expansion similar to csh(1).
              -a      All subsequent variables that are defined are automatically exported.
              -b      Prints  job  completion  messages as soon as a background job changes state
                      rather than waiting for the next prompt.
              -e      Unless contained in a || or && command, or  the  command  following  an  if
                      while  or  until command or in the pipeline following !, if a command has a
                      non-zero exit status, execute the ERR trap, if set, and exit.  This mode is
                      disabled while reading profiles.
              -f      Disables pathname expansion.
              -h      Each command becomes a tracked alias when first encountered.
              -k      (Obsolete). All variable assignment arguments are placed in the environment
                      for a command, not just those that precede the command name.
              -m      Background jobs will run in a separate process group and a line will  print
                      upon  completion.  The exit status of background jobs is reported in a com-
                      pletion message.  On systems with job control, this option is turned on au-
                      tomatically for interactive shells.
              -n      Read  commands  and  check them for syntax errors, but do not execute them.
                      Ignored for interactive shells.
              -o      The following argument can be one of the following option names:
                      allexport
                              Same as -a.
                      backslashctrl
                              The backslash character \ escapes the next control character in the
                              emacs  built-in  editor and the next erase or kill character in the
                              vi built-in editor.  On by default.
                      bgnice  All background jobs are run at a lower priority.  This is  the  de-
                              fault mode.
                      braceexpand
                              Same as -B.
                      emacs   Puts you in an emacs style in-line editor for command entry.
                      errexit Same as -e.
                      globcasedetect
                              When  this  option  is  turned on, globbing (see Pathname Expansion
                              above) and file name listing and completion  (see  In-line  Editing
                              Options  above)  automatically become case-insensitive on file sys-
                              tems where the difference between upper- and lowercase  is  ignored
                              for  file  names.  This is transparently determined for each direc-
                              tory, so a path pattern that spans multiple  file  systems  can  be
                              part  case-sensitive  and  part  case-insensitive.  In more precise
                              terms, each  slash-separated  path  name  component  pattern  p  is
                              treated as ~(i:p) if its parent directory exists on a case-insensi-
                              tive file system.  This option is only present on operating systems
                              that support case-insensitive file systems.
                      globstar
                              Same as -G.
                      gmacs   Puts you in a gmacs style in-line editor for command entry.
                      histexpand
                              Same as -H.
                      ignoreeof
                              An  interactive  shell  will  not exit on end-of-file.  The command
                              exit must be used.
                      keyword Same as -k.
                      letoctal
                              The let command allows octal numbers starting with 0.   On  by  de-
                              fault if ksh is invoked as sh or rsh.
                      markdirs
                              All directory names resulting from pathname expansion have a trail-
                              ing / appended.
                      monitor Same as -m.
                      multiline
                              The built-in editors will use multiple  lines  on  the  screen  for
                              lines  that  are longer than the width of the screen.  This may not
                              work for all terminals.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.
                      nolog   Obsolete; has no effect.
                      notify  Same as -b.
                      nounset Same as -u.
                      pipefail
                              A pipeline will not complete until all components of  the  pipeline
                              have  completed, and the return value will be the value of the last
                              non-zero command to fail or zero if no command has failed.
                      posix   Enables the POSIX standard  mode  for  maximum  compatibility  with
                              other  compliant  shells.  At  the  moment that the posix option is
                              turned on, it also turns on letoctal and turns off  -B/braceexpand;
                              the  reverse  is done when posix is turned back off. (These options
                              can still be controlled independently in between.) Furthermore, the
                              posix  option  is automatically turned on upon invocation if ksh is
                              invoked as sh or rsh. In that case, or if the option is  turned  on
                              by  specifying -o posix on the invocation command line, the invoked
                              shell will not set the preset aliases even if interactive, and will
                              not  import  type  attributes  for  variables  (such  as integer or
                              left/right justify) from the environment.
                              In addition, while on, the posix option
                              o  disables exporting variable type attributes to  the  environment
                                 for other ksh processes to import;
                              o  causes  file  descriptors  > 2 to be left open when invoking an-
                                 other program;
                              o  disables the &> redirection shorthand;
                              o  makes the <> redirection operator default to  redirecting  stan-
                                 dard input if no file descriptor number precedes it;
                              o  disables  the  special  floating  point constants Inf and NaN in
                                 arithmetic evaluation so that, e.g., $((inf)) and $((nan)) refer
                                 to the variables by those names;
                              o  enables  the recognition of a leading zero as introducing an oc-
                                 tal number in all arithmetic evaluation contexts, except in  the
                                 let built-in while letoctal is off;
                              o  stops  the  . command (but not source) from looking up functions
                                 defined with the function syntax;
                              o  changes the test/[ built-in command to make its deprecated expr1
                                 -a  expr2 and expr1 -o expr2 operators work even if expr1 equals
                                 "!" or "(" (which means the nonstandard unary -a file and -o op-
                                 tion  operators cannot be directly negated using ! or wrapped in
                                 parentheses); and
                              o  disables a hack that makes test -t ([ -t ]) equivalent  to  test
                                 -t 1 ([ -t 1 ]).
                      privileged
                              Same as -p.
                      showme  When  enabled, simple commands or pipelines preceded by a semicolon
                              (;) will be displayed as if the xtrace option were enabled but will
                              not be executed.  Otherwise, the leading ; will be ignored.
                      trackall
                              Same as -h.
                      verbose Same as -v.
                      vi      Puts  you in insert mode of a vi style in-line editor until you hit
                              the escape character 033.  This puts you in control mode.  A return
                              sends the line.
                      viraw   Each  character  is processed as it is typed in vi mode.  The shell
                              may have been compiled to force this option on at all times.   Oth-
                              erwise,  canonical processing (line-by-line input) is initially en-
                              abled and the command line will be echoed again  if  the  speed  is
                              1200 baud or greater and it contains any control characters or less
                              than one second has elapsed since the prompt was printed.  The  ESC
                              character  terminates canonical processing for the remainder of the
                              command and the user can then modify the command line. This  scheme
                              has  the  advantages  of  canonical  processing with the type-ahead
                              echoing of raw mode. If the viraw option is set, the terminal  will
                              always  have  canonical processing disabled.  This mode is implicit
                              for systems that do not support two alternate end  of  line  delim-
                              iters, and may be helpful for certain terminals.
                      xtrace  Same as -x.
                      If  no  option  name  is  supplied,  then  the  current option settings are
                      printed.
              -p      Disables  processing  of  the  $HOME/.profile  file  and  uses   the   file
                      /etc/suid_profile  instead  of  the ENV file.  This mode is on whenever the
                      effective uid (gid) is not equal to the real uid (gid).  Turning  this  off
                      causes the effective uid and gid to be set to the real uid and gid.
              -r      Enables the restricted shell.  This option cannot be unset once set.
              -s      Sort the positional parameters lexicographically.
              -t      (Obsolete).  Exit after reading and executing one command.
              -u      Treat  unset  parameters  as an error when substituting.  $@ and $* are ex-
                      empt.
              -v      Print shell input lines as they are read.
              -x      Print commands and their arguments as they are executed.
              --      Do not change any of the options; useful in setting $1 to a value beginning
                      with  -.  If no arguments follow this option then the positional parameters
                      are unset.

              As an obsolete feature, if the first arg is - then the -x and -v options are turned
              off  and  the  next  arg  is  treated as the first argument.  Using + rather than -
              causes these options to be turned off.  These options can also be used upon invoca-
              tion  of  the  shell.  The current set of options may be found in $-.  Unless -A is
              specified, the remaining arguments are positional parameters and are  assigned,  in
              order,  to  $1 $2 ....  If no arguments are given, then the names and values of all
              variables are printed on the standard output.

       <*> shift [ n ]
              The positional parameters from $n+1 ...  are renamed $1 ... , default n is 1.   The
              parameter  n can be any arithmetic expression that evaluates to a non-negative num-
              ber less than or equal to $#.

       sleep [ -s ] duration
              Suspends execution for the number of decimal seconds or fractions of a second given
              by duration.  duration can be an integer, floating point value or ISO 8601 duration
              specifying the length of time to sleep.  The option -s causes the sleep builtin  to
              terminate when it receives any signal.  If duration is not specified in conjunction
              with -s, sleep will wait for a signal indefinitely.

       source name [ arg ... ]
              Same as ., except it is not treated as a special built-in command.

       stop job ...
              Sends a SIGSTOP signal to one or more processes specified by job,  suspending  them
              until they receive SIGCONT.  The same as kill -s STOP.

       suspend
              Sends  a  SIGSTOP  signal to the main shell process, suspending the script or child
              shell session until it receives SIGCONT (for instance, when typing fg in the parent
              shell). Equivalent to kill -s STOP "$$", except that it accepts no operands and re-
              fuses to suspend a login shell.

       test expression
              The test and [ commands execute conditional expressions similar to those  specified
              for  the  [[ compound command under Conditional Expressions above, but with several
              important differences. The =, == and !=  operators  test  for  string  (in)equality
              without  pattern matching; == is nonstandard and unportable. The f3&& and || opera-
              tors are not available. Instead, the -a and -o binary operators can  be  used,  but
              they  are fraught with pitfalls due to grammatical ambiguities and therefore depre-
              cated in favor of invoking separate test commands. Most importantly, as test and  [
              are  simple  regular commands, field splitting and pathname expansion are performed
              on all their arguments and all aspects of regular shell grammar (such as  redirect-
              ion)  remain  active. This is usually harmful, so care must be taken to quote argu-
              ments and expansions to avoid this. To avoid the many pitfalls arising  from  these
              issues,  the [[ compound command should be used instead. The primary purpose of the
              test and [ commands is compatibility with other shells that lack [[.

              The test/[ command does not parse options except if there are two arguments and the
              second  is --. To access the inline documentation with an option such as --man, you
              need one of the forms test --man -- or [ --man -- ].

       times  Displays the accumulated user and system CPU times, one line with the times used by
              the shell and another with those used by all of the shell's child processes. No op-
              tions are supported.

       <*> trap [ -p ] [ action ] [ sig ] ...
              The -p option causes the trap action associated with each trap as specified by  the
              arguments  to  be printed with appropriate quoting.  Otherwise, action will be pro-
              cessed as if it were an argument to eval when the  shell  receives  signal(s)  sig.
              Each  sig can be given as a number or as the name of the signal.  Trap commands are
              executed in order of signal number.  Any attempt to set a trap on a signal that was
              ignored on entry to the current shell is ineffective.  If action is omitted and the
              first sig is a number, or if action is -, then the trap(s) for each sig  are  reset
              to their original values.  If action is the null string then this signal is ignored
              by the shell and by the commands it invokes.  If sig is ERR then action will be ex-
              ecuted  whenever a command has a non-zero exit status.  If sig is DEBUG then action
              will be executed before each command.  The variable .sh.command  will  contain  the
              current  command line when action is running, in the same format as the output gen-
              erated by the xtrace option (minus the preceding PS4 prompt).  If the  exit  status
              of  the trap is 2 the command will not be executed.  If the exit status of the trap
              is 255 and inside a function or a dot script, the function or dot script  will  re-
              turn.   If sig is 0 or EXIT and the trap statement is executed inside the body of a
              function defined with the function name syntax, then the command action is executed
              after the function completes.  If sig is 0 or EXIT for a trap set outside any func-
              tion then the command action is executed on exit from the shell.  If sig is  KEYBD,
              then  action  will  be executed whenever a key is read while in emacs, gmacs, or vi
              mode.  The trap command with no arguments prints a list of commands associated with
              each signal number.

       An  exit  or  return without an argument in a trap action will preserve the exit status of
       the command that invoked the trap.

       true   Does nothing, and exits 0. Used with while for infinite loops.

       type [ -afpq ] name ...
              The same as whence -v.

       <*><**> typeset [ +-ACHSbflmnprstux ] [ +-EFLRXZi[n] ]   [ +-M  [ mapname  ]  ]  [  -T   [
       tname=(assign_list) ] ] [ -h str ] [ -a [type] ] [ vname[=value ]  ] ...
              Sets  attributes and values for shell variables and functions.  When invoked inside
              a function defined with the function name syntax, a new instance  of  the  variable
              vname  is created, and the variable's value and type are restored when the function
              completes.  The following list of attributes may be specified:
              -A     Declares vname to be an associative array.  Subscripts  are  strings  rather
                     than arithmetic expressions.
              -C     Causes each vname to be a compound variable. If value names a compound vari-
                     able, it is copied into vname.  Otherwise, the empty compound value  is  as-
                     signed to vname.
              -a     Declares vname to be an indexed array.  If type is specified, it must be the
                     name of an enumeration type created with the enum command and it allows enu-
                     meration constants to be used as subscripts.
              -E     Declares vname to be a double precision floating point number.  If n is non-
                     zero, it defines the number of significant figures that are  used  when  ex-
                     panding vname.  Otherwise, ten significant figures will be used.
              -F     Declares vname to be a double precision floating point number.  If n is non-
                     zero, it defines the number of places after the decimal point that are  used
                     when  expanding vname.  Otherwise ten places after the decimal point will be
                     used.
              -H     This option provides UNIX to host-name file mapping on non-UNIX machines.
              -L     Left justify and remove leading blanks from value.  If n is non-zero, it de-
                     fines the width of the field, otherwise it is determined by the width of the
                     value of first assignment.  When the variable is assigned to, it  is  filled
                     on  the right with blanks or truncated, if necessary, to fit into the field.
                     The -R option is turned off.
              -M     Use the character mapping mapping defined by wctrans(3).   such  as  tolower
                     and  toupper when assigning a value to each of the specified operands.  When
                     mapping is specified and there are not operands, all variables that use this
                     mapping  are  written to standard output.  When mapping is omitted and there
                     are no operands, all mapped variables are written to standard output.
              -R     Right justify and fill with leading blanks.  If n is  non-zero,  it  defines
                     the width of the field, otherwise it is determined by the width of the value
                     of first assignment.  The field is left filled with blanks or truncated from
                     the end if the variable is reassigned.  The -L option is turned off.
              -S     When  used within the assign_list of a type definition, it causes the speci-
                     fied subvariable to be shared by all instances of the type.  When  used  in-
                     side a function defined with the function reserved word, the specified vari-
                     ables will have function static scope.  Otherwise,  the  variable  is  unset
                     prior to processing the assignment list.
              -T     If  followed  by  tname, it creates a type named by tname using the compound
                     assignment assign_list to tname.  Otherwise, it writes all the type  defini-
                     tions to standard output.
              -X     Declares  vname  to  be a double precision floating point number and expands
                     using the %a format of ISO-C99.  If n is non-zero, it defines the number  of
                     hex digits after the radix point that is used when expanding vname.  The de-
                     fault is 10.
              -Z     Right justify and fill with leading zeros if the first  non-blank  character
                     is  a digit and the -L option has not been set.  Remove leading zeros if the
                     -L option is also set.  If n is non-zero, it defines the width of the field,
                     otherwise it is determined by the width of the value of first assignment.
              -f     The  names  refer  to function names rather than variable names.  No assign-
                     ments can be made and the only other valid options are -S, -t,  -u  and  -x.
                     The  -S  can be used with discipline functions defined in a type to indicate
                     that the function is static.  For a static function, the same method will be
                     used  by  all instances of that type no matter which instance references it.
                     In addition, it can only use value of variables from the original type defi-
                     nition.   These  discipline  functions  cannot  be redefined in any type in-
                     stance.  The -t option turns on execution tracing for this function.  The -u
                     option causes this function to be marked undefined.  The FPATH variable will
                     be searched to find the function definition when the function is referenced.
                     If  no options other than -f is specified, then the function definition will
                     be displayed on standard output.  If +f is specified, then a line containing
                     the function name followed by a shell comment containing the line number and
                     path name of the file where this function was defined, if any, is displayed.
                     The  exit status can be used to determine whether the function is defined so
                     that typeset -f .sh.math.name will return 0 when math function name  is  de-
                     fined and non-zero otherwise.
              -b     The  variable can hold any number of bytes of data.  The data can be text or
                     binary.  The value is represented by the base64 encoding of the data.  If -Z
                     is  also  specified, the size in bytes of the data in the buffer will be de-
                     termined by the size associated with the -Z.  If the base64 string  assigned
                     results  in  more  data, it will be truncated.  Otherwise, it will be filled
                     with bytes whose value is zero.  The printf format %B can be used to  output
                     the actual data in this buffer instead of the base64 encoding of the data.
              -h     Used  within type definitions to add information when generating information
                     about the subvariable on the man page.  It is ignored when used outside of a
                     type  definition.   When used with -f the information is associated with the
                     corresponding discipline function.
              -i     Declares vname to be represented internally as integer.  The right hand side
                     of  an assignment is evaluated as an arithmetic expression when assigning to
                     an integer.  If n is non-zero, it defines the output arithmetic base, other-
                     wise the output base will be ten.
              -l     Used with -i, -E or -F, to indicate long integer, or long float.  Otherwise,
                     all uppercase characters are converted to lowercase.  The uppercase  option,
                     -u, is turned off.  Equivalent to -M tolower .
              -m     moves  or  renames  the variable.  The value is the name of a variable whose
                     value will be moved to vname.  The original variable will be unset.   Cannot
                     be used with any other options.
              -n     Declares  vname  to  be a reference to the variable whose name is defined by
                     the value of variable vname.  This is usually used to reference  a  variable
                     inside a function whose name has been passed as an argument.  Cannot be used
                     with any other options.
              -p     The name, attributes and values for the given vnames are written on standard
                     output  in a form that can be used as shell input.  If +p is specified, then
                     the values are not displayed.
              -r     The given vnames are marked read-only and these names cannot be  changed  by
                     subsequent assignment.
              -s     When given along with -i, restricts integer size to short.
              -t     Tags  the variables.  Tags are user definable and have no special meaning to
                     the shell.
              -u     When given along with -i, specifies unsigned integer.  Otherwise, all lower-
                     case  characters  are  converted to uppercase.  The lowercase option, -l, is
                     turned off.  Equivalent to -M toupper .
              -x     The given vnames are marked for automatic export to the environment of  sub-
                     sequently-executed  commands.   Variables whose names contain a .  cannot be
                     exported.

              The -i, -F, -E, and -X options cannot be specified along with -R, -L, or  -Z.   The
              -b option cannot be specified along with -L, -u, or -l.  The -f, -m, -n, and -T op-
              tions cannot be used together with any other option.

              Using + rather than - causes these options to be turned off.  If no vname arguments
              are  given,  a  list  of  vnames  (and  optionally  the values) of the variables is
              printed.  (Using + rather than - keeps the values from being printed.)  The -p  op-
              tion  causes  typeset followed by the option letters to be printed before each name
              rather than the names of the options.  If any option other than -p is  given,  only
              those  variables  which  have all of the given options are printed.  Otherwise, the
              vnames and attributes of all variables that have attributes are printed.

       ulimit [ -HSaMctdfxlqenupmrbiswTv ] [ limit ]
              Set or display a resource limit.  The available resource limits are  listed  below.
              Many systems do not support one or more of these limits.  The limit for a specified
              resource is set when limit is specified.  The value of limit can be a number in the
              unit specified below with each resource, or the value unlimited.  The -H and -S op-
              tions specify whether the hard limit or the soft limit for the  given  resource  is
              set.   A  hard  limit  cannot be increased once it is set.  A soft limit can be in-
              creased up to the value of the hard limit.  If neither the H nor S option is speci-
              fied,  the limit applies to both.  The current resource limit is printed when limit
              is omitted.  In this case, the soft limit is printed unless H is  specified.   When
              more than one resource is specified, then the limit name and unit is printed before
              the value.
              -a     Lists all of the current resource limits.
              -b     The socket buffer size in bytes.
              -c     The number of 512-byte blocks on the size of core dumps.
              -d     The number of K-bytes on the size of the data area.
              -e     The scheduling priority.
              -f     The number of 512-byte blocks on files that can be written  by  the  current
                     process or by child processes (files of any size may be read).
              -i     The signal queue size.
              -l     The locked address space in K-bytes.
              -M     The address space limit in K-bytes.
              -m     The number of K-bytes on the size of physical memory.
              -n     The number of file descriptors plus 1.
              -p     The number of 512-byte blocks for pipe buffering.
              -q     The message queue size in K-bytes.
              -r     The max real-time priority.
              -s     The number of K-bytes on the size of the stack area.
              -T     The number of threads.
              -t     The number of CPU seconds to be used by each process.
              -u     The number of processes.
              -v     The number of K-bytes for virtual memory.
              -w     The swap size in K-bytes.
              -x     The number of file locks.

              If no option is given, -f is assumed.

       umask [ -S ] [ mask ]
              The  user  file-creation mask is set to mask (see umask(2)).  mask can either be an
              octal number or a symbolic value as described in chmod(1).  If a symbolic value  is
              given,  the new umask value is the complement of the result of applying mask to the
              complement of the previous umask value.  If mask is omitted, the current  value  of
              the  mask  is  printed.   The -S option causes the mode to be printed as a symbolic
              value.  Otherwise, the mask is printed in octal.

       unalias [ -a ] name ...
              The aliases given by the list of names are removed from the alias list.  The -a op-
              tion causes all the aliases to be unset.

       <*> unset [ -fnv ] vname ...
              The variables given by the list of vnames are unassigned, i.e., except for subvari-
              ables within a type, their values and attributes are erased.  For subvariables of a
              type, the values are reset to the default value from the type definition.  Readonly
              variables cannot be unset.  If the -f option is set, then the names refer to  func-
              tion  names.  If the -v option is set, then the names refer to variable names.  The
              -f option overrides -v.  If -n is set and name is a name reference, then name  will
              be unset rather than the variable that it references.  The default is equivalent to
              -v.  Unsetting LINENO, MAILCHECK, OPTARG, OPTIND, RANDOM, SECONDS, TMOUT, and _ re-
              moves their special meaning even if they are subsequently assigned to.

       wait [ job ... ]
              Wait for the specified job and report its termination status.  If job is not given,
              then all currently active child processes are waited for.   The  exit  status  from
              this  command is that of the last process waited for if job is specified; otherwise
              it is zero.  See Jobs for a description of the format of job.

       whence [ -afpqv ] name ...
              For each name, indicate how it would be interpreted if used as a command name.
              The -v option produces a more verbose report.  The -f option skips the  search  for
              functions.   The  -p option does a path search for name even if name is an alias, a
              function, or a reserved word.  The -p option turns off the -v option.  The  -q  op-
              tion  causes  whence to enter quiet mode.  whence will return zero if all arguments
              are built-ins, functions, or are programs found on the path.  The -a option is sim-
              ilar  to  the  -v option but causes all interpretations of the given name to be re-
              ported.

   Invocation.
       If the shell is invoked by exec(2), initialization depends on argument zero ($0)  as  fol-
       lows.  If the first character of $0 is -, or the -l option is given on the invocation com-
       mand line, then the shell is assumed to be a login shell.  If the basename of the  command
       path  in  $0 is rsh, rksh, or krsh, then the shell becomes restricted.  If the basename is
       sh or rsh, or the -o posix option is given on the invocation command line, then the  shell
       is  initialized  in full POSIX compliance mode (see the set builtin command above for more
       information).  After this, if the shell was assumed to be a login shell, commands are read
       from /etc/profile and then from $HOME/.profile if it exists.  Alternatively, the option -l
       causes the shell to be treated as a login shell.  Next, for interactive  shells,  commands
       are  read from the file named by ENV if the file exists, its name being determined by per-
       forming parameter expansion, command substitution, and arithmetic expansion on  the  value
       of  that  environment variable.  If the -s option is not present and arg and a file by the
       name of arg exists, then it reads and executes this script.  Otherwise, if the  first  arg
       does not contain a /, a path search is performed on the first arg to determine the name of
       the script to execute.  The script arg must have execute permission  and  any  setuid  and
       setgid settings will be ignored.  If the script is not found on the path, arg is processed
       as if it named a built-in command or function.  Commands are then read as described below;
       the following options are interpreted by the shell when it is invoked:

       -D      A  list  of  all double quoted strings that are preceded by a $ will be printed on
               standard output and the shell will exit.  This set of strings will be  subject  to
               language  translation when the locale is not C or POSIX.  No commands will be exe-
               cuted.

       -E or -o rc or --rc
               Read the file named by the ENV variable or by $HOME/.kshrc if  not  defined  after
               the  profiles.   On  by default for interactive shells. Use +E, +o rc or --norc to
               turn off.

       -c      Read and execute a script from the first arg instead of a file.  The  second  arg,
               if  present,  becomes that script's command name ($0).  Any third and further args
               become positional parameters starting at $1.

       -s      Read and execute a script from standard input instead of a file.  The command name
               ($0)  cannot  be  set.   Any args become the positional parameters starting at $1.
               This option is forced on if no arg is given and is ignored if -c  is  also  speci-
               fied.

       -i or -o interactive or --interactive
               If  the  -i  option is present or if the shell's standard input and standard error
               are attached to a terminal (as told by tcgetattr(3)), then this shell is  interac-
               tive.   In  this case TERM is ignored (so that kill 0 does not kill an interactive
               shell) and INTR is caught and ignored (so that wait  is  interruptible).   In  all
               cases, QUIT is ignored by the shell.

       -r or -o restricted or --restricted
               If the -r option is present, the shell is a restricted shell.

       The  remaining  options  and  arguments are described under the set command above.  An op-
       tional - as the first argument is ignored.

   Rksh Only.
       Rksh is used to set up login names and execution environments whose capabilities are  more
       controlled  than  those of the standard shell.  The actions of rksh are identical to those
       of ksh, except that the following are disallowed:
              unsetting the restricted option,
              changing directory (see cd(1)),
              setting or unsetting the value or attributes of SHELL, ENV, FPATH, or PATH,
              specifying path or command names containing /,
              redirecting output (>, >|, <>, and >>),
              adding or deleting built-in commands,
              using command -p to invoke a command.

       The restrictions above are enforced after .profile and the ENV files are interpreted.

       When a command to be executed is found to be a shell procedure, rksh invokes ksh  to  exe-
       cute  it.   Thus, it is possible to provide to the end-user shell procedures that have ac-
       cess to the full power of the standard shell, while imposing a limited menu  of  commands;
       this  scheme  assumes that the end-user does not have write and execute permissions in the
       same directory.

       The net effect of these rules is that the writer of the .profile has complete control over
       user  actions, by performing guaranteed setup actions and leaving the user in an appropri-
       ate directory (probably not the login directory).

       The system administrator often sets up a directory of commands (e.g., /usr/rbin) that  can
       be safely invoked by rksh.

EXIT STATUS
       Errors  detected by the shell, such as syntax errors, cause the shell to return a non-zero
       exit status.  If the shell is being used non-interactively, then execution  of  the  shell
       file  is abandoned unless the error occurs inside a subshell in which case the subshell is
       abandoned.  Otherwise, the shell returns the exit status of the last command executed (see
       also  the  exit  command  above).   Run  time errors detected by the shell are reported by
       printing the command or function name and the error condition.  If the  line  number  that
       the  error occurred on is greater than one, then the line number is also printed in square
       brackets ([]) after the command or function name.

FILES
       /etc/profile
              The system wide initialization file, executed for login shells.

       $HOME/.profile
              The personal initialization file, executed for login shells after /etc/profile.

       $HOME/.kshrc
              Default personal initialization file, executed for interactive shells when  ENV  is
              not set.

       /etc/suid_profile
              Alternative  initialization  file,  executed instead of the personal initialization
              file when the real and effective user or group id do not match.

       /dev/null
              NULL device

SEE ALSO
       cat(1), cd(1), chmod(1), cut(1), date(1), egrep(1), echo(1), emacs(1),  env(1),  fgrep(1),
       gmacs(1),  grep(1),  stty(1),  test(1),  umask(1), vi(1), dup(2), exec(2), fork(2), getpw-
       nam(3),  ioctl(2),  lseek(2),  paste(1),  pathconf(2),  pipe(2),   sysconf(3),   umask(2),
       ulimit(2), wait(2), strftime(3), wctrans(3), rand(3), profile(5), environ(7).

       Morris  I.  Bolsky  and David G. Korn, The New KornShell Command and Programming Language,
       Prentice Hall, 1995.

       POSIX - Part 2: Shell and Utilities, IEEE Std 1003.2-1992, ISO/IEC 9945-2, IEEE, 1993.

CAVEATS
       If a command is executed, and then a command with the same name is installed in  a  direc-
       tory  in  the  search  path before the directory where the original command was found, the
       shell will continue to exec the original command.  Use the hash command or the  -t  option
       of the alias command to correct this situation.

       Some very old shell scripts contain a ^ as a synonym for the pipe character |.

       Using  the hist built-in command within a compound command will cause the whole command to
       disappear from the history file.

       The built-in command . file reads the whole file before any commands are executed.  There-
       fore, alias and unalias commands in the file will not apply to any commands defined in the
       file.

       Traps are not processed while a job is waiting for a foreground process.  Thus, a trap  on
       CHLD won't be executed until the foreground job terminates.

       It  is  a good idea to leave a space after the comma operator in arithmetic expressions to
       prevent the comma from being interpreted as the decimal point  character  in  certain  lo-
       cales.

                                                                                           KSH(1)

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