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bc(1)                                General Commands Manual                                bc(1)

NAME
       bc - An arbitrary precision calculator language

SYNTAX
       bc [ -hlwsqv ] [long-options] [  file ... ]

DESCRIPTION
       bc  is  a language that supports arbitrary precision numbers with interactive execution of
       statements.  There are some similarities in the syntax to the C programming  language.   A
       standard math library is available by command line option.  If requested, the math library
       is defined before processing any files.  bc starts by processing code from all  the  files
       listed  on  the command line in the order listed.  After all files have been processed, bc
       reads from the standard input.  All code is executed as it is read.  (If a file contains a
       command to halt the processor, bc will never read from the standard input.)

       This  version  of bc contains several extensions beyond traditional bc implementations and
       the POSIX draft standard.  Command line options can cause  these  extensions  to  print  a
       warning  or to be rejected.  This document describes the language accepted by this proces-
       sor.  Extensions will be identified as such.

   OPTIONS
       -h, --help
              Print the usage and exit.

       -i, --interactive
              Force interactive mode.

       -l, --mathlib
              Define the standard math library.

       -w, --warn
              Give warnings for extensions to POSIX bc.

       -s, --standard
              Process exactly the POSIX bc language.

       -q, --quiet
              Do not print the normal GNU bc welcome.

       -v, --version
              Print the version number and copyright and quit.

   NUMBERS
       The most basic element in bc is the number.   Numbers  are  arbitrary  precision  numbers.
       This  precision is both in the integer part and the fractional part.  All numbers are rep-
       resented internally in decimal and all computation is  done  in  decimal.   (This  version
       truncates  results from divide and multiply operations.)  There are two attributes of num-
       bers, the length and the scale.  The length is the total number of decimal digits used  by
       bc  to  represent  a  number and the scale is the total number of decimal digits after the
       decimal point.  For example:
               .000001 has a length of 6 and scale of 6.
               1935.000 has a length of 7 and a scale of 3.

   VARIABLES
       Numbers are stored in two types of variables, simple variables and  arrays.   Both  simple
       variables and array variables are named.  Names begin with a letter followed by any number
       of letters, digits and underscores.  All letters must be lower case.  (Full  alpha-numeric
       names  are an extension.  In POSIX bc all names are a single lower case letter.)  The type
       of variable is clear by the context because all array variable names will be  followed  by
       brackets ([]).

       There  are  four special variables, scale, ibase, obase, and last.  scale defines how some
       operations use digits after the decimal point.  The default value of scale  is  0.   ibase
       and  obase  define the conversion base for input and output numbers.  The default for both
       input and output is base 10.  last (an extension) is a variable that has the value of  the
       last printed number.  These will be discussed in further detail where appropriate.  All of
       these variables may have values assigned to them as well as used in expressions.

   COMMENTS
       Comments in bc start with the characters /* and end with the characters */.  Comments  may
       start  anywhere  and  appear as a single space in the input.  (This causes comments to de-
       limit other input items.  For example, a comment can not be found in the middle of a vari-
       able  name.)  Comments include any newlines (end of line) between the start and the end of
       the comment.

       To support the use of scripts for bc, a single line comment has been added  as  an  exten-
       sion.   A single line comment starts at a # character and continues to the next end of the
       line.  The end of line character is not part of the comment and is processed normally.

   EXPRESSIONS
       The numbers are manipulated by expressions and statements.  Since  the  language  was  de-
       signed  to  be  interactive,  statements and expressions are executed as soon as possible.
       There is no "main" program.  Instead, code is executed as it is encountered.   (Functions,
       discussed in detail later, are defined when encountered.)

       A  simple  expression is just a constant. bc converts constants into internal decimal num-
       bers using the current input base, specified by the variable ibase. (There is an exception
       in  functions.)  The legal values of ibase are 2 through 36. (Bases greater than 16 are an
       extension.) Assigning a value outside this range to ibase will result in a value of  2  or
       36.   Input  numbers may contain the characters 0-9 and A-Z. (Note: They must be capitals.
       Lower case letters are variable names.)  Single digit numbers always have the value of the
       digit  regardless  of  the  value  of  ibase.  (i.e. A = 10.)  For multi-digit numbers, bc
       changes all input digits greater or equal to ibase to the value of  ibase-1.   This  makes
       the number ZZZ always be the largest 3 digit number of the input base.

       Full  expressions are similar to many other high level languages.  Since there is only one
       kind of number, there are no rules for mixing types.  Instead,  there  are  rules  on  the
       scale  of  expressions.   Every expression has a scale.  This is derived from the scale of
       original numbers, the operation performed and in many cases, the  value  of  the  variable
       scale. Legal values of the variable scale are 0 to the maximum number representable by a C
       integer.

       In the following descriptions of legal expressions, "expr" refers to a complete expression
       and "var" refers to a simple or an array variable.  A simple variable is just a
              name
       and an array variable is specified as
              name[expr]
       Unless  specifically mentioned the scale of the result is the maximum scale of the expres-
       sions involved.

       - expr The result is the negation of the expression.

       ++ var The variable is incremented by one and the new value is the result of  the  expres-
              sion.

       -- var The  variable  is decremented by one and the new value is the result of the expres-
              sion.

       var ++
               The result of the expression is the value of the variable and then the variable is
              incremented by one.

       var -- The  result of the expression is the value of the variable and then the variable is
              decremented by one.

       expr + expr
              The result of the expression is the sum of the two expressions.

       expr - expr
              The result of the expression is the difference of the two expressions.

       expr * expr
              The result of the expression is the product of the two expressions.

       expr / expr
              The result of the expression is the quotient of the two expressions.  The scale  of
              the result is the value of the variable scale.

       expr % expr
              The result of the expression is the "remainder" and it is computed in the following
              way.  To compute a%b, first a/b is computed to scale digits.  That result  is  used
              to  compute  a-(a/b)*b  to the scale of the maximum of scale+scale(b) and scale(a).
              If scale is set to zero and both expressions are integers this  expression  is  the
              integer remainder function.

       expr ^ expr
              The  result  of the expression is the value of the first raised to the second.  The
              second expression must be an integer.  (If the second expression is not an integer,
              a  warning  is  generated and the expression is truncated to get an integer value.)
              The scale of the result is scale if the exponent is negative.  If the  exponent  is
              positive  the  scale of the result is the minimum of the scale of the first expres-
              sion times the value of the exponent and the maximum of scale and the scale of  the
              first  expression.  (e.g. scale(a^b) = min(scale(a)*b, max( scale, scale(a))).)  It
              should be noted that expr^0 will always return the value of 1.

       ( expr )
              This alters the standard precedence to force the evaluation of the expression.

       var = expr
              The variable is assigned the value of the expression.

       var <op>= expr
              This is equivalent to "var = var <op> expr" with the exception that the "var"  part
              is evaluated only once.  This can make a difference if "var" is an array.

       Relational  expressions are a special kind of expression that always evaluate to 0 or 1, 0
       if the relation is false and 1 if the relation is true.  These may appear in any legal ex-
       pression.   (POSIX bc requires that relational expressions are used only in if, while, and
       for statements and that only one relational test may be done in them.)  The relational op-
       erators are

       expr1 < expr2
              The result is 1 if expr1 is strictly less than expr2.

       expr1 <= expr2
              The result is 1 if expr1 is less than or equal to expr2.

       expr1 > expr2
              The result is 1 if expr1 is strictly greater than expr2.

       expr1 >= expr2
              The result is 1 if expr1 is greater than or equal to expr2.

       expr1 == expr2
              The result is 1 if expr1 is equal to expr2.

       expr1 != expr2
              The result is 1 if expr1 is not equal to expr2.

       Boolean  operations are also legal.  (POSIX bc does NOT have boolean operations).  The re-
       sult of all boolean operations are 0 and 1 (for false and true) as in  relational  expres-
       sions.  The boolean operators are:

       !expr  The result is 1 if expr is 0.

       expr && expr
              The result is 1 if both expressions are non-zero.

       expr || expr
              The result is 1 if either expression is non-zero.

       The expression precedence is as follows: (lowest to highest)
              || operator, left associative
              && operator, left associative
              ! operator, nonassociative
              Relational operators, left associative
              Assignment operator, right associative
              + and - operators, left associative
              *, / and % operators, left associative
              ^ operator, right associative
              unary - operator, nonassociative
              ++ and -- operators, nonassociative

       This  precedence  was chosen so that POSIX compliant bc programs will run correctly.  This
       will cause the use of the relational and logical operators to have some  unusual  behavior
       when used with assignment expressions.  Consider the expression:
              a = 3 < 5

       Most  C  programmers would assume this would assign the result of "3 < 5" (the value 1) to
       the variable "a".  What this does in bc is assign the value 3 to the variable "a" and then
       compare 3 to 5.  It is best to use parenthesis when using relational and logical operators
       with the assignment operators.

       There are a few more special expressions that are provided in bc.  These have to  do  with
       user  defined  functions  and  standard functions.  They all appear as "name(parameters)".
       See the section on functions for user defined functions.  The standard functions are:

       length ( expression )
              The value of the length function is the number of significant digits in the expres-
              sion.

       read ( )
              The  read  function  (an extension) will read a number from the standard input, re-
              gardless of where the function occurs.   Beware, this can cause problems  with  the
              mixing  of  data and program in the standard input.  The best use for this function
              is in a previously written program that needs input from the user, but never allows
              program code to be input from the user.  The value of the read function is the num-
              ber read from the standard input using the current value of the variable ibase  for
              the conversion base.

       scale ( expression )
              The  value of the scale function is the number of digits after the decimal point in
              the expression.

       sqrt ( expression )
              The value of the sqrt function is the square root of the expression.   If  the  ex-
              pression is negative, a run time error is generated.

   STATEMENTS
       Statements  (as  in most algebraic languages) provide the sequencing of expression evalua-
       tion.  In bc statements are executed "as soon as possible."  Execution happens when a new-
       line  in  encountered and there is one or more complete statements.  Due to this immediate
       execution, newlines are very important in bc.  In fact, both a semicolon and a newline are
       used  as  statement  separators.   An improperly placed newline will cause a syntax error.
       Because newlines are statement separators, it is possible to hide a newline by  using  the
       backslash  character.   The  sequence  "\<nl>", where <nl> is the newline appears to bc as
       whitespace instead of a newline.  A statement list is a series of statements separated  by
       semicolons  and  newlines.   The  following  is  a list of bc statements and what they do:
       (Things enclosed in brackets ([]) are optional parts of the statement.)

       expression
              This statement does one of two things.  If the expression starts  with  "<variable>
              <assignment>  ...", it is considered to be an assignment statement.  If the expres-
              sion is not an assignment statement, the expression is evaluated and printed to the
              output.   After the number is printed, a newline is printed.  For example, "a=1" is
              an assignment statement and "(a=1)" is an expression that has an  embedded  assign-
              ment.   All numbers that are printed are printed in the base specified by the vari-
              able obase.  The legal values for obase are 2 through BC_BASE_MAX.  (See  the  sec-
              tion LIMITS.)  For bases 2 through 16, the usual method of writing numbers is used.
              For bases greater than 16, bc uses a multi-character digit method of  printing  the
              numbers  where  each  higher base digit is printed as a base 10 number.  The multi-
              character digits are separated by spaces.  Each digit contains the number of  char-
              acters required to represent the base ten value of "obase-1".  Since numbers are of
              arbitrary precision, some numbers may not be printable on  a  single  output  line.
              These  long  numbers will be split across lines using the "\" as the last character
              on a line.  The maximum number of characters printed per line is 70.   Due  to  the
              interactive nature of bc, printing a number causes the side effect of assigning the
              printed value to the special variable last.  This allows the user  to  recover  the
              last value printed without having to retype the expression that printed the number.
              Assigning to last is legal and will overwrite the last printed value with  the  as-
              signed  value.   The  newly  assigned  value  will  remain until the next number is
              printed or another value is assigned to last.  (Some installations  may  allow  the
              use  of  a single period (.) which is not part of a number as a short hand notation
              for for last.)

       string The string is printed to the output.  Strings start with a double  quote  character
              and  contain  all characters until the next double quote character.  All characters
              are take literally, including any newline.  No newline character is  printed  after
              the string.

       print list
              The  print  statement (an extension) provides another method of output.  The "list"
              is a list of strings and expressions separated by commas.  Each string  or  expres-
              sion  is printed in the order of the list.  No terminating newline is printed.  Ex-
              pressions are evaluated and their value is printed and  assigned  to  the  variable
              last.   Strings  in  the  print statement are printed to the output and may contain
              special characters.  Special characters start with  the  backslash  character  (\).
              The  special  characters recognized by bc are "a" (alert or bell), "b" (backspace),
              "f" (form feed), "n" (newline), "r" (carriage  return),  "q"  (double  quote),  "t"
              (tab),  and  "\"  (backslash).  Any other character following the backslash will be
              ignored.

       { statement_list }
              This is the compound statement.  It allows multiple statements to  be  grouped  to-
              gether for execution.

       if ( expression ) statement1 [else statement2]
              The if statement evaluates the expression and executes statement1 or statement2 de-
              pending on the value of the expression.  If the expression is non-zero,  statement1
              is  executed.   If statement2 is present and the value of the expression is 0, then
              statement2 is executed.  (The else clause is an extension.)

       while ( expression ) statement
              The while statement will execute the statement while the  expression  is  non-zero.
              It  evaluates  the expression before each execution of the statement.   Termination
              of the loop is caused by a zero expression value or the execution of a break state-
              ment.

       for ( [expression1] ; [expression2] ; [expression3] ) statement
              The  for  statement  controls  repeated execution of the statement.  Expression1 is
              evaluated before the loop.  Expression2 is evaluated before each execution  of  the
              statement.  If it is non-zero, the statement is evaluated.  If it is zero, the loop
              is terminated.  After each execution of the statement, expression3 is evaluated be-
              fore  the  reevaluation of expression2.  If expression1 or expression3 are missing,
              nothing is evaluated at the point they would be evaluated.  If expression2 is miss-
              ing, it is the same as substituting the value 1 for expression2.  (The optional ex-
              pressions are an extension.  POSIX bc requires all three expressions.)  The follow-
              ing is equivalent code for the for statement:
              expression1;
              while (expression2) {
                 statement;
                 expression3;
              }

       break  This statement causes a forced exit of the most recent enclosing while statement or
              for statement.

       continue
              The continue statement (an extension) causes the most recent enclosing  for  state-
              ment to start the next iteration.

       halt   The  halt statement (an extension) is an executed statement that causes the bc pro-
              cessor to quit only when it is executed.  For example, "if (0 == 1) halt" will  not
              cause bc to terminate because the halt is not executed.

       return Return the value 0 from a function.  (See the section on functions.)

       return ( expression )
              Return  the  value  of  the  expression from a function.  (See the section on func-
              tions.)  As an extension, the parenthesis are not required.

   PSEUDO STATEMENTS
       These statements are not statements in the  traditional  sense.   They  are  not  executed
       statements.  Their function is performed at "compile" time.

       limits Print the local limits enforced by the local version of bc.  This is an extension.

       quit   When  the  quit  statement  is  read, the bc processor is terminated, regardless of
              where the quit statement is found.  For example, "if (0 == 1) quit" will  cause  bc
              to terminate.

       warranty
              Print a longer warranty notice.  This is an extension.

   FUNCTIONS
       Functions  provide  a  method of defining a computation that can be executed later.  Func-
       tions in bc always compute a value and return it to the caller.  Function definitions  are
       "dynamic"  in  the sense that a function is undefined until a definition is encountered in
       the input.  That definition is then used until another definition function  for  the  same
       name  is  encountered.  The new definition then replaces the older definition.  A function
       is defined as follows:
              define name ( parameters ) { newline
                  auto_list   statement_list }
       A function call is just an expression of the form "name(parameters)".

       Parameters are numbers or arrays (an extension).  In the function definition, zero or more
       parameters  are  defined  by  listing their names separated by commas.  All parameters are
       call by value parameters.  Arrays are specified in the parameter definition by  the  nota-
       tion  "name[]".    In the function call, actual parameters are full expressions for number
       parameters.  The same notation is used for passing arrays as for  defining  array  parame-
       ters.  The named array is passed by value to the function.  Since function definitions are
       dynamic, parameter numbers and types are checked when a function is called.  Any  mismatch
       in  number  or  types of parameters will cause a runtime error.  A runtime error will also
       occur for the call to an undefined function.

       The auto_list is an optional list of variables that are for "local" use.   The  syntax  of
       the auto list (if present) is "auto name, ... ;".  (The semicolon is optional.)  Each name
       is the name of an auto variable.  Arrays may be specified by using the  same  notation  as
       used in parameters.  These variables have their values pushed onto a stack at the start of
       the function.  The variables are then initialized to zero and used throughout  the  execu-
       tion  of  the function.  At function exit, these variables are popped so that the original
       value (at the time of the function call) of these variables are restored.  The  parameters
       are  really  auto variables that are initialized to a value provided in the function call.
       Auto variables are different than traditional local variables because if function A  calls
       function  B,  B may access function A's auto variables by just using the same name, unless
       function B has called them auto variables.  Due to the fact that auto variables and param-
       eters are pushed onto a stack, bc supports recursive functions.

       The  function  body  is a list of bc statements.  Again, statements are separated by semi-
       colons or newlines.  Return statements cause the termination of a function and the  return
       of  a  value.   There are two versions of the return statement.  The first form, "return",
       returns the value 0 to the calling expression.  The second form, "return ( expression  )",
       computes  the  value  of  the expression and returns that value to the calling expression.
       There is an implied "return (0)" at the end of every function.  This allows a function  to
       terminate and return 0 without an explicit return statement.

       Functions also change the usage of the variable ibase.  All constants in the function body
       will be converted using the value of ibase at the time of the function call.   Changes  of
       ibase  will  be ignored during the execution of the function except for the standard func-
       tion read, which will always use the current value of ibase for conversion of numbers.

       Several extensions have been added to functions.  First, the format of the definition  has
       been slightly relaxed.  The standard requires the opening brace be on the same line as the
       define keyword and all other parts must be on following lines.  This version  of  bc  will
       allow  any number of newlines before and after the opening brace of the function.  For ex-
       ample, the following definitions are legal.
              define d (n) { return (2*n); }
              define d (n)
                { return (2*n); }

       Functions may be defined as void.  A void function returns no value and thus  may  not  be
       used  in  any  place that needs a value.  A void function does not produce any output when
       called by itself on an input line.  The key word void is placed between the key  word  de-
       fine and the function name.  For example, consider the following session.
              define py (y) { print "--->", y, "<---", "\n"; }
              define void px (x) { print "--->", x, "<---", "\n"; }
              py(1)
              --->1<---
              0
              px(1)
              --->1<---
       Since  py  is  not  a  void function, the call of py(1) prints the desired output and then
       prints a second line that is the value of the function.  Since the  value  of  a  function
       that  is  not given an explicit return statement is zero, the zero is printed.  For px(1),
       no zero is printed because the function is a void function.

       Also, call by variable for arrays was added.  To declare a call  by  variable  array,  the
       declaration  of  the array parameter in the function definition looks like "*name[]".  The
       call to the function remains the same as call by value arrays.

   MATH LIBRARY
       If bc is invoked with the -l option, a math library is preloaded and the default scale  is
       set  to 20.   The math functions will calculate their results to the scale set at the time
       of their call.  The math library defines the following functions:

       s (x)  The sine of x, x is in radians.

       c (x)  The cosine of x, x is in radians.

       a (x)  The arctangent of x, arctangent returns radians.

       l (x)  The natural logarithm of x.

       e (x)  The exponential function of raising e to the value x.

       j (n,x)
              The Bessel function of integer order n of x.

   EXAMPLES
       In /bin/sh, the following will assign the value of "pi" to the shell variable pi.
               pi=$(echo "scale=10; 4*a(1)" | bc -l)

       The following is the definition of the exponential function  used  in  the  math  library.
       This function is written in POSIX bc.
              scale = 20

              /* Uses the fact that e^x = (e^(x/2))^2
                 When x is small enough, we use the series:
                   e^x = 1 + x + x^2/2! + x^3/3! + ...
              */

              define e(x) {
                auto  a, d, e, f, i, m, v, z

                /* Check the sign of x. */
                if (x<0) {
                  m = 1
                  x = -x
                }

                /* Precondition x. */
                z = scale;
                scale = 4 + z + .44*x;
                while (x > 1) {
                  f += 1;
                  x /= 2;
                }

                /* Initialize the variables. */
                v = 1+x
                a = x
                d = 1

                for (i=2; 1; i++) {
                  e = (a *= x) / (d *= i)
                  if (e == 0) {
                    if (f>0) while (f--)  v = v*v;
                    scale = z
                    if (m) return (1/v);
                    return (v/1);
                  }
                  v += e
                }
              }

       The  following is code that uses the extended features of bc to implement a simple program
       for calculating checkbook balances.  This program is best kept in a file so that it can be
       used many times without having to retype it at every use.
              scale=2
              print "\nCheck book program!\n"
              print "  Remember, deposits are negative transactions.\n"
              print "  Exit by a 0 transaction.\n\n"

              print "Initial balance? "; bal = read()
              bal /= 1
              print "\n"
              while (1) {
                "current balance = "; bal
                "transaction? "; trans = read()
                if (trans == 0) break;
                bal -= trans
                bal /= 1
              }
              quit

       The following is the definition of the recursive factorial function.
              define f (x) {
                if (x <= 1) return (1);
                return (f(x-1) * x);
              }

   READLINE AND LIBEDIT OPTIONS
       GNU  bc  can be compiled (via a configure option) to use the GNU readline input editor li-
       brary or the BSD libedit library.  This allows the user to  do  editing  of  lines  before
       sending  them to bc.  It also allows for a history of previous lines typed.  When this op-
       tion is selected, bc has one more special variable.  This special variable, history is the
       number  of lines of history retained.  For readline, a value of -1 means that an unlimited
       number of history lines are retained.  Setting the value of history to a  positive  number
       restricts  the  number  of history lines to the number given.  The value of 0 disables the
       history feature.  The default value is 100.  For more information, read the  user  manuals
       for the GNU readline, history and BSD libedit libraries.  One can not enable both readline
       and libedit at the same time.

   DIFFERENCES
       This version of bc was implemented from the POSIX P1003.2/D11 draft and  contains  several
       differences  and  extensions relative to the draft and traditional implementations.  It is
       not implemented in the traditional way using dc(1).  This  version  is  a  single  process
       which  parses and runs a byte code translation of the program.  There is an "undocumented"
       option (-c) that causes the program to output the byte code to the standard output instead
       of  running  it.   It  was mainly used for debugging the parser and preparing the math li-
       brary.

       A major source of differences is extensions, where a feature is extended to add more func-
       tionality  and additions, where new features are added.  The following is the list of dif-
       ferences and extensions.

       LANG environment
              This version does not conform to the POSIX standard in the processing of  the  LANG
              environment variable and all environment variables starting with LC_.

       names  Traditional  and POSIX bc have single letter names for functions, variables and ar-
              rays.  They have been extended to be multi-character names that start with a letter
              and may contain letters, numbers and the underscore character.

       Strings
              Strings  are not allowed to contain NUL characters.  POSIX says all characters must
              be included in strings.

       last   POSIX bc does not have a last variable.  Some implementations of bc use the  period
              (.) in a similar way.

       comparisons
              POSIX  bc allows comparisons only in the if statement, the while statement, and the
              second expression of the for statement.  Also, only one relational operation is al-
              lowed in each of those statements.

       if statement, else clause
              POSIX bc does not have an else clause.

       for statement
              POSIX bc requires all expressions to be present in the for statement.

       &&, ||, !
              POSIX bc does not have the logical operators.

       read function
              POSIX bc does not have a read function.

       print statement
              POSIX bc does not have a print statement.

       continue statement
              POSIX bc does not have a continue statement.

       return statement
              POSIX bc requires parentheses around the return expression.

       array parameters
              POSIX  bc does not (currently) support array parameters in full.  The POSIX grammar
              allows for arrays in function definitions, but does not provide a method to specify
              an  array  as  an actual parameter.  (This is most likely an oversight in the gram-
              mar.)  Traditional implementations of bc have only call by value array parameters.

       function format
              POSIX bc requires the opening brace on the same line as the define key word and the
              auto statement on the next line.

       =+, =-, =*, =/, =%, =^
              POSIX  bc  does  not  require these "old style" assignment operators to be defined.
              This version may allow these "old style" assignments.  Use the limits statement  to
              see if the installed version supports them.  If it does support the "old style" as-
              signment operators, the statement "a =- 1" will decrement a by 1 instead of setting
              a to the value -1.

       spaces in numbers
              Other  implementations  of  bc allow spaces in numbers.  For example, "x=1 3" would
              assign the value 13 to the variable x.  The same statement would cause a syntax er-
              ror in this version of bc.

       errors and execution
              This implementation varies from other implementations in terms of what code will be
              executed when syntax and other errors are found in the program.  If a syntax  error
              is  found in a function definition, error recovery tries to find the beginning of a
              statement and continue to parse the function.  Once a syntax error is found in  the
              function,  the  function will not be callable and becomes undefined.  Syntax errors
              in the interactive execution code will invalidate the current execution block.  The
              execution  block  is terminated by an end of line that appears after a complete se-
              quence of statements.  For example,
              a = 1
              b = 2
       has two execution blocks and
              { a = 1
                b = 2 }
       has one execution block.  Any runtime error will terminate the execution  of  the  current
       execution block.  A runtime warning will not terminate the current execution block.

       Interrupts
              During an interactive session, the SIGINT signal (usually generated by the control-
              C character from the terminal) will cause execution of the current execution  block
              to be interrupted.  It will display a "runtime" error indicating which function was
              interrupted.  After all runtime structures have been cleaned up, a message will  be
              printed to notify the user that bc is ready for more input.  All previously defined
              functions remain defined and the value of all non-auto variables are the  value  at
              the  point of interruption.  All auto variables and function parameters are removed
              during the clean up process.  During a non-interactive session, the  SIGINT  signal
              will terminate the entire run of bc.

   LIMITS
       The  following  are the limits currently in place for this bc processor.  Some of them may
       have been changed by an installation.  Use the limits statement to see the actual values.

       BC_BASE_MAX
              The maximum output base is currently set at 999.  The maximum input base is 16.

       BC_DIM_MAX
              This is currently an arbitrary limit of 65535 as  distributed.   Your  installation
              may be different.

       BC_SCALE_MAX
              The  number  of digits after the decimal point is limited to INT_MAX digits.  Also,
              the number of digits before the decimal point is limited to INT_MAX digits.

       BC_STRING_MAX
              The limit on the number of characters in a string is INT_MAX characters.

       exponent
              The value of the exponent in the raise operation (^) is limited to LONG_MAX.

       variable names
              The current limit on the number of unique names is 32767 for each of  simple  vari-
              ables, arrays and functions.

ENVIRONMENT VARIABLES
       The following environment variables are processed by bc:

       POSIXLY_CORRECT
              This is the same as the -s option.

       BC_ENV_ARGS
              This  is  another  mechanism to get arguments to bc.  The format is the same as the
              command line arguments.  These arguments are processed first, so any  files  listed
              in  the environment arguments are processed before any command line argument files.
              This allows the user to set up "standard" options and files to be processed at  ev-
              ery  invocation of bc.  The files in the environment variables would typically con-
              tain function definitions for functions the user wants defined  every  time  bc  is
              run.

       BC_LINE_LENGTH
              This should be an integer specifying the number of characters in an output line for
              numbers.  This includes the backslash and newline characters for long numbers.   As
              an  extension,  the value of zero disables the multi-line feature.  Any other value
              of this variable that is less than 3 sets the line length to 70.

DIAGNOSTICS
       If any file on the command line can not be opened, bc will report that  the  file  is  un-
       available  and terminate.  Also, there are compile and run time diagnostics that should be
       self-explanatory.

BUGS
       Error recovery is not very good yet.

       Email bug reports to bug-bc AT gnu.org.  Be sure to include the word ``bc'' somewhere in  the
       ``Subject:'' field.

AUTHOR
       Philip A. Nelson
       philnelson AT acm.org

ACKNOWLEDGEMENTS
       The  author  would  like  to thank Steve Sommars (Steve.Sommars AT att.com) for his extensive
       help in testing the implementation.  Many great suggestions were given.  This  is  a  much
       better product due to his involvement.

GNU Project                                 2006-06-11                                      bc(1)

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