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ZSHTCPSYS(1)                         General Commands Manual                         ZSHTCPSYS(1)

NAME
       zshtcpsys - zsh tcp system

DESCRIPTION
       A module zsh/net/tcp is provided to provide network I/O over TCP/IP from within the shell;
       see its description in zshmodules(1).  This manual page describes a function  suite  based
       on  the  module.   If  the module is installed, the functions are usually installed at the
       same time, in which case they will be available for autoloading in  the  default  function
       search path.  In addition to the zsh/net/tcp module, the zsh/zselect module is used to im-
       plement timeouts on read operations.  For troubleshooting tips, consult the  corresponding
       advice for the zftp functions described in zshzftpsys(1).

       There  are functions corresponding to the basic I/O operations open, close, read and send,
       named tcp_open etc., as well as a function tcp_expect for pattern match analysis  of  data
       read  as  input.   The system makes it easy to receive data from and send data to multiple
       named sessions at once.  In addition, it can be linked with the  shell's  line  editor  in
       such  a  way  that  input  data  is automatically shown at the terminal.  Other facilities
       available including logging, filtering and configurable output prompts.

       To use the system where it is available, it should be enough to `autoload -U tcp_open' and
       run  tcp_open as documented below to start a session.  The tcp_open function will autoload
       the remaining functions.

TCP USER FUNCTIONS
   Basic I/O
       tcp_open [ -qz ] host port [ sess ]
       tcp_open [ -qz ] [ -s sess | -l sess[,...] ] ...
       tcp_open [ -qz ] [ -a fd | -f fd ] [ sess ]
              Open a new session.  In the first and simplest form, open a TCP connection to  host
              host at port port; numeric and symbolic forms are understood for both.

              If  sess  is given, this becomes the name of the session which can be used to refer
              to multiple different TCP connections.  If sess is not given, the function will in-
              vent  a  numeric  name  value  (note this is not the same as the file descriptor to
              which the session is attached).  It is recommended that session names  not  include
              `funny'  characters,  where  funny characters are not well-defined but certainly do
              not include alphanumerics or underscores, and certainly do include whitespace.

              In the second case, one or more sessions to be opened are given by name.  A  single
              session  name  is  given after -s and a comma-separated list after -l; both options
              may be repeated as many times as necessary.  A failure to open any  session  causes
              tcp_open  to abort.  The host and port are read from the file .ztcp_sessions in the
              same directory as the user's zsh initialisation files, i.e. usually the home direc-
              tory,  but  $ZDOTDIR if that is set.  The file consists of lines each giving a ses-
              sion name and the corresponding host and port, in that order (note the session name
              comes first, not last), separated by whitespace.

              The  third form allows passive and fake TCP connections.  If the option -a is used,
              its argument is a file descriptor open for listening for connections.  No  function
              front-end  is provided to open such a file descriptor, but a call to `ztcp -l port'
              will create one with the file descriptor stored in the parameter $REPLY.  The  lis-
              tening port can be closed with `ztcp -c fd'.  A call to `tcp_open -a fd' will block
              until a remote TCP connection is made to port on the local machine.  At this point,
              a  session is created in the usual way and is largely indistinguishable from an ac-
              tive connection created with one of the first two forms.

              If the option -f is used, its argument is a file descriptor which is used  directly
              as  if  it  were  a TCP session.  How well the remainder of the TCP function system
              copes with this depends on what actually underlies this file descriptor.  A regular
              file  is  likely  to  be unusable; a FIFO (pipe) of some sort will work better, but
              note that it is not a good idea for two different sessions to attempt to read  from
              the same FIFO at once.

              If  the option -q is given with any of the three forms, tcp_open will not print in-
              formational messages, although it will in any case exit with an appropriate status.

              If the line editor (zle) is in use, which is typically the case if the shell is in-
              teractive,  tcp_open installs a handler inside zle which will check for new data at
              the same time as it checks for keyboard input.  This is  convenient  as  the  shell
              consumes  no CPU time while waiting; the test is performed by the operating system.
              Giving the option -z to any of the forms of tcp_open prevents the handler from  be-
              ing  installed, so data must be read explicitly.  Note, however, this is not neces-
              sary for executing complete sets of send and read commands from a function, as  zle
              is  not  active at this point.  Generally speaking, the handler is only active when
              the shell is waiting for input at a command prompt or in the  vared  builtin.   The
              option has no effect if zle is not active; `[[ -o zle]]' will test for this.

              The  first session to be opened becomes the current session and subsequent calls to
              tcp_open do not change  it.   The  current  session  is  stored  in  the  parameter
              $TCP_SESS; see below for more detail about the parameters used by the system.

              The  function tcp_on_open, if defined, is called when a session is opened.  See the
              description below.

       tcp_close [ -qn ] [ -a | -l sess[,...] | sess ... ]
              Close the named sessions, or the current session if none is given, or all open ses-
              sions  if -a is given.  The options -l and -s are both handled for consistency with
              tcp_open, although the latter is redundant.

              If the session being closed is the current one, $TCP_SESS is unset, leaving no cur-
              rent session, even if there are other sessions still open.

              If  the  session was opened with tcp_open -f, the file descriptor is closed so long
              as it is in the range 0 to 9 accessible directly from the command line.  If the op-
              tion  -n  is given, no attempt will be made to close file descriptors in this case.
              The -n option is not used for genuine ztcp session; the file descriptors are always
              closed with the session.

              If the option -q is given, no informational messages will be printed.

       tcp_read [ -bdq ] [ -t TO ] [ -T TO ]
                [ -a | -u fd[,...] | -l sess[,...] | -s sess ... ]
              Perform  a  read  operation on the current session, or on a list of sessions if any
              are given with -u, -l or -s, or all open sessions if the option -a is  given.   Any
              of the -u, -l or -s options may be repeated or mixed together.  The -u option spec-
              ifies a file descriptor directly (only those managed by this  system  are  useful),
              the other two specify sessions as described for tcp_open above.

              The  function checks for new data available on all the sessions listed.  Unless the
              -b option is given, it will not block waiting for new data.  Any one line  of  data
              from any of the available sessions will be read, stored in the parameter $TCP_LINE,
              and displayed to standard output unless $TCP_SILENT contains  a  non-empty  string.
              When  printed  to standard output the string $TCP_PROMPT will be shown at the start
              of the line; the default form for this includes the name of the session being read.
              See  below for more information on these parameters.  In this mode, tcp_read can be
              called repeatedly until it returns status 2 which indicates all pending input  from
              all specified sessions has been handled.

              With  the option -b, equivalent to an infinite timeout, the function will block un-
              til a line is available to read from one of the specified sessions.  However,  only
              a single line is returned.

              The  option  -d  indicates  that all pending input should be drained.  In this case
              tcp_read may process multiple lines in the manner given above;  only  the  last  is
              stored  in $TCP_LINE, but the complete set is stored in the array $tcp_lines.  This
              is cleared at the start of each call to tcp_read.

              The options -t and -T specify a timeout in seconds, which may be a  floating  point
              number  for  increased  accuracy.   With -t the timeout is applied before each line
              read.  With -T, the timeout applies to the overall  operation,  possibly  including
              multiple read operations if the option -d is present; without this option, there is
              no distinction between -t and -T.

              The function does not print informational messages, but if the option -q is  given,
              no error message is printed for a non-existent session.

              A  return  status  of 2 indicates a timeout or no data to read.  Any other non-zero
              return status indicates some error condition.

              See tcp_log for how to control where data is sent by tcp_read.

       tcp_send [ -cnq ] [ -s sess | -l sess[,...] ] data ...
       tcp_send [ -cnq ] -a data ...
              Send the supplied data strings to all the specified sessions in turn.  The underly-
              ing  operation  differs  little from a `print -r' to the session's file descriptor,
              although it attempts to prevent the shell from dying owing to a SIGPIPE  caused  by
              an attempt to write to a defunct session.

              The option -c causes tcp_send to behave like cat.  It reads lines from standard in-
              put until end of input and sends them in turn to the specified  session(s)  exactly
              as if they were given as data arguments to individual tcp_send commands.

              The  option  -n  prevents  tcp_send  from  putting a newline at the end of the data
              strings.

              The remaining options all behave as for tcp_read.

              The data arguments are  not  further  processed  once  they  have  been  passed  to
              tcp_send; they are simply passed down to print -r.

              If  the parameter $TCP_OUTPUT is a non-empty string and logging is enabled then the
              data sent to each session will be echoed to the log  file(s)  with  $TCP_OUTPUT  in
              front where appropriate, much in the manner of $TCP_PROMPT.

   Session Management
       tcp_alias [ -q ] alias=sess ...
       tcp_alias [ -q ] [ alias ... ]
       tcp_alias -d [ -q ] alias ...
              This function is not particularly well tested.

              The first form creates an alias for a session name; alias can then be used to refer
              to the existing session sess.  As many aliases may be listed as required.

              The second form lists any aliases specified, or all aliases if none.

              The third form deletes all the aliases listed.  The underlying sessions are not af-
              fected.

              The option -q suppresses an inconsistently chosen subset of error messages.

       tcp_log [ -asc ] [ -n | -N ] [ logfile ]
              With  an  argument  logfile,  all  future input from tcp_read will be logged to the
              named file.  Unless -a (append) is given, this file will first be truncated or cre-
              ated empty.  With no arguments, show the current status of logging.

              With  the option -s, per-session logging is enabled.  Input from tcp_read is output
              to the file logfile.sess.  As the session is  automatically  discriminated  by  the
              filename,  the contents are raw (no $TCP_PROMPT).  The option  -a applies as above.
              Per-session logging and logging of all data in one file are not mutually exclusive.

              The option -c closes all logging, both complete and per-session logs.

              The options -n and -N respectively turn off or  restore  output  of  data  read  by
              tcp_read to standard output; hence `tcp_log -cn' turns off all output by tcp_read.

              The  function  is purely a convenient front end to setting the parameters $TCP_LOG,
              $TCP_LOG_SESS, $TCP_SILENT, which are described below.

       tcp_rename old new
              Rename session old to session new.  The old name becomes invalid.

       tcp_sess [ sess [ command [ arg ... ] ] ]
              With no arguments, list all the open sessions and associated file descriptors.  The
              current  session is marked with a star.  For use in functions, direct access to the
              parameters $tcp_by_name, $tcp_by_fd and $TCP_SESS is probably more convenient;  see
              below.

              With  a  sess  argument,  set  the  current session to sess.  This is equivalent to
              changing $TCP_SESS directly.

              With additional arguments, temporarily set  the  current  session  while  executing
              `command  arg  ...'.  command is re-evaluated so as to expand aliases etc., but the
              remaining args are passed through as that appear to tcp_sess.  The original session
              is restored when tcp_sess exits.

   Advanced I/O
       tcp_command send-option ... send-argument ...
              This  is a convenient front-end to tcp_send.  All arguments are passed to tcp_send,
              then the function pauses waiting for data.  While data is arriving at  least  every
              $TCP_TIMEOUT  (default  0.3)  seconds, data is handled and printed out according to
              the current settings.  Status 0 is always returned.

              This is generally only useful for interactive use, to prevent the display  becoming
              fragmented  by output returned from the connection.  Within a programme or function
              it is generally better to handle reading data by a more explicit method.

       tcp_expect [ -q ] [ -p var | -P var ] [ -t TO | -T TO ]
                  [ -a | -s sess | -l sess[,...] ] pattern ...
              Wait for input matching any of the given patterns from any of  the  specified  ses-
              sions.   Input is ignored until an input line matches one of the given patterns; at
              this point status zero is returned, the matching line is stored in  $TCP_LINE,  and
              the  full  set  of  lines read during the call to tcp_expect is stored in the array
              $tcp_expect_lines.

              Sessions are specified in the same way as tcp_read: the default is to use the  cur-
              rent session, otherwise the sessions specified by -a, -s, or -l are used.

              Each  pattern is a standard zsh extended-globbing pattern; note that it needs to be
              quoted to avoid it being expanded immediately  by  filename  generation.   It  must
              match  the  full line, so to match a substring there must be a `*' at the start and
              end.  The line matched against includes the $TCP_PROMPT added by tcp_read.   It  is
              possible  to  include the globbing flags `#b' or `#m' in the patterns to make back-
              references available in the parameters $MATCH, $match, etc., as  described  in  the
              base zsh documentation on pattern matching.

              Unlike tcp_read, the default behaviour of tcp_expect is to block indefinitely until
              the required input is found.  This can be modified by specifying a timeout with  -t
              or -T; these function as in tcp_read, specifying a per-read or overall timeout, re-
              spectively, in seconds, as an integer or floating-point number.  As  tcp_read,  the
              function returns status 2 if a timeout occurs.

              The function returns as soon as any one of the patterns given match.  If the caller
              needs to know which of the patterns matched, the option -p var can be used; on  re-
              turn,  $var  is  set to the number of the pattern using ordinary zsh indexing, i.e.
              the first is 1, and so on.  Note the absence of a `$' in front of  var.   To  avoid
              clashes,  the parameter cannot begin with `_expect'.  The index -1 is used if there
              is a timeout and 0 if there is no match.

              The option -P var works similarly to -p, but instead of numerical indexes the regu-
              lar  arguments  must  begin  with a prefix followed by a colon: that prefix is then
              used as a tag to which var is set when the argument matches.  The  tag  timeout  is
              used  if  there is a timeout and the empty string if there is no match.  Note it is
              acceptable for different arguments to start with the same prefix if the matches  do
              not need to be distinguished.

              The option -q is passed directly down to tcp_read.

              As  all  input is done via tcp_read, all the usual rules about output of lines read
              apply.  One exception is that the parameter $tcp_lines will only reflect  the  line
              actually  matched  by  tcp_expect;  use $tcp_expect_lines for the full set of lines
              read during the function call.

       tcp_proxy
              This is a simple-minded function to accept a TCP connection and execute  a  command
              with I/O redirected to the connection.  Extreme caution should be taken as there is
              no security whatsoever and this can leave your computer open to  the  world.   Ide-
              ally, it should only be used behind a firewall.

              The first argument is a TCP port on which the function will listen.

              The  remaining  arguments give a command and its arguments to execute with standard
              input, standard output and standard error redirected  to  the  file  descriptor  on
              which  the  TCP  session  has  been accepted.  If no command is given, a new zsh is
              started.  This gives everyone on your network direct access to your account,  which
              in many cases will be a bad thing.

              The command is run in the background, so tcp_proxy can then accept new connections.
              It continues to accept new connections until interrupted.

       tcp_spam [ -ertv ] [ -a | -s sess | -l sess[,...] ] cmd [ arg ... ]
              Execute `cmd [ arg ... ]' for each session in turn.  Note this executes the command
              and  arguments;  it does not send the command line as data unless the -t (transmit)
              option is given.

              The sessions may be selected explicitly with the standard -a, -s or -l options,  or
              may  be  chosen  implicitly.   If none of the three options is given the rules are:
              first, if the array $tcp_spam_list is set, this is taken as the list  of  sessions,
              otherwise  all  sessions  are  taken.   Second,  any  sessions  given  in the array
              $tcp_no_spam_list are removed from the list of sessions.

              Normally, any sessions added by the `-a' flag or when all sessions are  chosen  im-
              plicitly  are spammed in alphabetic order; sessions given by the $tcp_spam_list ar-
              ray or on the command line are spammed in the order given.  The  -r  flag  reverses
              the order however it was arrived it.

              The  -v flag specifies that a $TCP_PROMPT will be output before each session.  This
              is output after any modification to TCP_SESS by the user-defined tcp_on_spam  func-
              tion  described  below.   (Obviously that function is able to generate its own out-
              put.)

              If the option -e is present, the line given as `cmd [ arg ... ]' is executed  using
              eval, otherwise it is executed without any further processing.

       tcp_talk
              This  is  a  fairly  simple-minded  attempt to force input to the line editor to go
              straight to the default TCP_SESS.

              An escape string, $TCP_TALK_ESCAPE, default `:', is used to allow access to  normal
              shell operation.  If it is on its own at the start of the line, or followed only by
              whitespace, the line editor returns to normal operation.  Otherwise, the string and
              any  following  whitespace  are  skipped  and the remainder of the line executed as
              shell input without any change of the line editor's operating mode.

              The current implementation is somewhat deficient in terms of  use  of  the  command
              history.   For  this reason, many users will prefer to use some form of alternative
              approach for sending data easily to the current session.  One simple approach is to
              alias some special character (such as `%') to `tcp_command --'.

       tcp_wait
              The sole argument is an integer or floating point number which gives the seconds to
              delay.  The shell will do nothing for that period except wait for input on all  TCP
              sessions  by  calling tcp_read -a.  This is similar to the interactive behaviour at
              the command prompt when zle handlers are installed.

   `One-shot' file transfer
       tcp_point port
       tcp_shoot host port
              This pair of functions provide a simple way to transfer a file  between  two  hosts
              within  the  shell.  Note, however, that bulk data transfer is currently done using
              cat.  tcp_point reads any data arriving at port and sends it  to  standard  output;
              tcp_shoot  connects  to port on host and sends its standard input.  Any unused port
              may be used; the standard mechanism for picking a port is  to  think  of  a  random
              four-digit number above 1024 until one works.

              To transfer a file from host woodcock to host springes, on springes:

                     tcp_point 8091 >output_file

              and on woodcock:

                     tcp_shoot springes 8091 <input_file

              As  these  two  functions do not require tcp_open to set up a TCP connection first,
              they may need to be autoloaded separately.

TCP USER-DEFINED FUNCTIONS
       Certain functions, if defined by the user, will be called by the function system  in  cer-
       tain contexts.  This facility depends on the module zsh/parameter, which is usually avail-
       able in interactive shells as the completion system depends on it.  None of the  functions
       need be defined; they simply provide convenient hooks when necessary.

       Typically, these are called after the requested action has been taken, so that the various
       parameters will reflect the new state.

       tcp_on_alias alias fd
              When an alias is defined, this function will be called with two arguments: the name
              of the alias, and the file descriptor of the corresponding session.

       tcp_on_awol sess fd
              If  the  function tcp_fd_handler is handling input from the line editor and detects
              that the file descriptor is no longer reusable, by default it removes it  from  the
              list of file descriptors handled by this method and prints a message.  If the func-
              tion tcp_on_awol is defined it is called immediately before this point.  It may re-
              turn  status  100,  which  indicates  that the normal handling should still be per-
              formed; any other return status indicates that no further action  should  be  taken
              and  the tcp_fd_handler should return immediately with the given status.  Typically
              the action of tcp_on_awol will be to close the session.

              The variable TCP_INVALIDATE_ZLE will be a non-empty string if it  is  necessary  to
              invalidate  the  line editor display using `zle -I' before printing output from the
              function.

              (`AWOL' is military jargon for `absent without leave' or some variation.  It has no
              pre-existing technical meaning known to the author.)

       tcp_on_close sess fd
              This  is  called  with  the  name of a session being closed and the file descriptor
              which corresponded to that session.  Both will be invalid by the time the  function
              is called.

       tcp_on_open sess fd
              This  is called after a new session has been defined with the session name and file
              descriptor as arguments.  If it returns a non-zero status, opening the  session  is
              assumed to fail and the session is closed again; however, tcp_open will continue to
              attempt to open any remaining sessions given on the command line.

       tcp_on_rename oldsess fd newsess
              This is called after a session has been renamed with the three arguments  old  ses-
              sion name, file descriptor, new session name.

       tcp_on_spam sess command ...
              This is called once for each session spammed, just before a command is executed for
              a session by tcp_spam.  The arguments are the session name followed by the  command
              list  to be executed.  If tcp_spam was called with the option -t, the first command
              will be tcp_send.

              This function is called after $TCP_SESS  is  set  to  reflect  the  session  to  be
              spammed, but before any use of it is made.  Hence it is possible to alter the value
              of $TCP_SESS within this function.  For example, the session arguments to  tcp_spam
              could include extra information to be stripped off and processed in tcp_on_spam.

              If  the  function sets the parameter $REPLY to `done', the command line is not exe-
              cuted; in addition, no prompt is printed for the -v option to tcp_spam.

       tcp_on_unalias alias fd
              This is called with the name of an alias and the corresponding session's  file  de-
              scriptor after an alias has been deleted.

TCP UTILITY FUNCTIONS
       The  following  functions are used by the TCP function system but will rarely if ever need
       to be called directly.

       tcp_fd_handler
              This is the function installed by tcp_open for handling input from within the  line
              editor,  if  that is required.  It is in the format documented for the builtin `zle
              -F' in zshzle(1) .

              While active, the function sets the parameter TCP_HANDLER_ACTIVE to 1.  This allows
              shell  code  called  internally (for example, by setting tcp_on_read) to tell if is
              being called when the shell is otherwise idle at the editor prompt.

       tcp_output [ -q ] -P prompt -F fd -S sess
              This function is used for both logging and handling output to standard output, from
              within tcp_read and (if $TCP_OUTPUT is set) tcp_send.

              The prompt to use is specified by -P; the default is the empty string.  It can con-
              tain:
              %c     Expands to 1 if the session is the current session, otherwise 0.  Used  with
                     ternary expressions such as `%(c.-.+)' to output `+' for the current session
                     and `-' otherwise.

              %f     Replaced by the session's file descriptor.

              %s     Replaced by the session name.

              %%     Replaced by a single `%'.

              The option -q suppresses output to standard output, but not to any log files  which
              are configured.

              The  -S and -F options are used to pass in the session name and file descriptor for
              possible replacement in the prompt.

TCP USER PARAMETERS
       Parameters follow the usual convention that uppercase is used for  scalars  and  integers,
       while lowercase is used for normal and associative array.  It is always safe for user code
       to read these parameters.  Some parameters may also be set; these  are  noted  explicitly.
       Others  are  included  in this group as they are set by the function system for the user's
       benefit, i.e. setting them is typically not useful but is benign.

       It is often also useful to make settable parameters local to  a  function.   For  example,
       `local TCP_SILENT=1' specifies that data read during the function call will not be printed
       to standard output, regardless of the setting  outside  the  function.   Likewise,  `local
       TCP_SESS=sess'  sets  a  session  for  the duration of a function, and `local TCP_PROMPT='
       specifies that no prompt is used for input during the function.

       tcp_expect_lines
              Array.  The set of lines read during the last call  to  tcp_expect,  including  the
              last ($TCP_LINE).

       tcp_filter
              Array.  May be set directly.  A set of extended globbing patterns which, if matched
              in tcp_output, will cause the line not to be printed to standard output.  The  pat-
              terns  should  be  defined as described for the arguments to tcp_expect.  Output of
              line to log files is not affected.

       TCP_HANDLER_ACTIVE
              Scalar.  Set to 1 within tcp_fd_handler to indicate to functions called recursively
              that they have been called during an editor session.  Otherwise unset.

       TCP_LINE
              The last line read by tcp_read, and hence also tcp_expect.

       TCP_LINE_FD
              The file descriptor from which $TCP_LINE was read.  ${tcp_by_fd[$TCP_LINE_FD]} will
              give the corresponding session name.

       tcp_lines
              Array. The set of lines read during the last call to tcp_read, including  the  last
              ($TCP_LINE).

       TCP_LOG
              May be set directly, although it is also controlled by tcp_log.  The name of a file
              to which output from all sessions will be sent.  The output  is  proceeded  by  the
              usual  $TCP_PROMPT.   If it is not an absolute path name, it will follow the user's
              current directory.

       TCP_LOG_SESS
              May be set directly, although it is also controlled by tcp_log.  The prefix  for  a
              set  of  files  to which output from each session separately will be sent; the full
              filename is ${TCP_LOG_SESS}.sess.  Output to each file is raw; no prompt is  added.
              If it is not an absolute path name, it will follow the user's current directory.

       tcp_no_spam_list
              Array.  May be set directly.  See tcp_spam for how this is used.

       TCP_OUTPUT
              May be set directly.  If a non-empty string, any data sent to a session by tcp_send
              will be logged.  This parameter gives the prompt to be used in a file specified  by
              $TCP_LOG but not in a file generated from $TCP_LOG_SESS.  The prompt string has the
              same format as TCP_PROMPT and the same rules for its use apply.

       TCP_PROMPT
              May be set directly.  Used as the prefix for data read by tcp_read which is printed
              to standard output or to the log file given by $TCP_LOG, if any.  Any `%s', `%f' or
              `%%' occurring in the string will be replaced by the name of the session, the  ses-
              sion's  underlying  file descriptor, or a single `%', respectively.  The expression
              `%c' expands to 1 if the session being read is the current session, else 0; this is
              most useful in ternary expressions such as `%(c.-.+)' which outputs `+' if the ses-
              sion is the current one, else `-'.

              If the prompt starts with %P, this is stripped and the complete result of the  pre-
              vious  stage is passed through standard prompt %-style formatting before being out-
              put.

       TCP_READ_DEBUG
              May be set directly.  If this has non-zero length, tcp_read will give some  limited
              diagnostics about data being read.

       TCP_SECONDS_START
              This value is created and initialised to zero by tcp_open.

              The  functions  tcp_read and tcp_expect use the shell's SECONDS parameter for their
              own timing purposes.  If that parameter is not of floating point type on  entry  to
              one  of  the  functions, it will create a local parameter SECONDS which is floating
              point and set the parameter TCP_SECONDS_START to the previous  value  of  $SECONDS.
              If  the  parameter is already floating point, it is used without a local copy being
              created and TCP_SECONDS_START is not set.  As the global value is zero,  the  shell
              elapsed time is guaranteed to be the sum of $SECONDS and $TCP_SECONDS_START.

              This  can  be  avoided  by setting SECONDS globally to a floating point value using
              `typeset -F SECONDS'; then the TCP functions will never make a local copy and never
              set TCP_SECONDS_START to a non-zero value.

       TCP_SESS
              May be set directly.  The current session; must refer to one of the sessions estab-
              lished by tcp_open.

       TCP_SILENT
              May be set directly, although it is also controlled by  tcp_log.   If  of  non-zero
              length,  data  read  by tcp_read will not be written to standard output, though may
              still be written to a log file.

       tcp_spam_list
              Array.  May be set directly.  See the description of the function tcp_spam for  how
              this is used.

       TCP_TALK_ESCAPE
              May  be set directly.  See the description of the function tcp_talk for how this is
              used.

       TCP_TIMEOUT
              May be set directly.  Currently this is only used by the function tcp_command,  see
              above.

TCP USER-DEFINED PARAMETERS
       The  following parameters are not set by the function system, but have a special effect if
       set by the user.

       tcp_on_read
              This should be an associative array; if it is  not,  the  behaviour  is  undefined.
              Each  key  is  the name of a shell function or other command, and the corresponding
              value is a shell pattern (using EXTENDED_GLOB).  Every line read from a TCP session
              directly  or indirectly using tcp_read (which includes lines read by tcp_expect) is
              compared against the pattern.  If the line matches, the command given in the key is
              called  with  two  arguments: the name of the session from which the line was read,
              and the line itself.

              If any function called to handle a line returns a non-zero status, the line is  not
              output.   Thus a tcp_on_read handler containing only the instruction `return 1' can
              be used to suppress output of particular lines (see,  however,  tcp_filter  above).
              However,  the line is still stored in TCP_LINE and tcp_lines; this occurs after all
              tcp_on_read processing.

TCP UTILITY PARAMETERS
       These parameters are controlled by the function system; they may  be  read  directly,  but
       should not usually be set by user code.

       tcp_aliases
              Associative  array.   The keys are the names of sessions established with tcp_open;
              each value is a space-separated list of aliases which refer to that session.

       tcp_by_fd
              Associative array.  The keys are session file descriptors; each value is  the  name
              of that session.

       tcp_by_name
              Associative  array.  The keys are the names of sessions; each value is the file de-
              scriptor associated with that session.

TCP EXAMPLES
       Here is a trivial example using a remote calculator.

       To create a calculator server on port 7337 (see the dc manual page for quite how infuriat-
       ing the underlying command is):

              tcp_proxy 7337 dc

       To connect to this from the same host with a session also named `dc':

              tcp_open localhost 7337 dc

       To  send a command to the remote session and wait a short while for output (assuming dc is
       the current session):

              tcp_command 2 4 + p

       To close the session:

              tcp_close

       The tcp_proxy needs to be killed to be stopped.  Note this will not usually kill any  con-
       nections  which  have  already  been  accepted,  and also that the port is not immediately
       available for reuse.

       The following chunk of code puts a list of sessions into an xterm header, with the current
       session followed by a star.

              print -n "\033]2;TCP:" ${(k)tcp_by_name:/$TCP_SESS/$TCP_SESS\*} "\a"

TCP BUGS
       The function tcp_read uses the shell's normal read builtin.  As this reads a complete line
       at once, data arriving without a terminating newline can cause the function to  block  in-
       definitely.

       Though  the  function  suite works well for interactive use and for data arriving in small
       amounts, the performance when large amounts of data are being exchanged is  likely  to  be
       extremely poor.

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