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ZSHTCPSYS(1)							  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 implement timeouts on read opera‐
       tions.  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 sys‐
       tem 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 ter‐
       minal.	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  invent  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 initiali‐
	      sation  files,  i.e. usually the home directory, but $ZDOTDIR if
	      that is set.  The file consists of lines each giving  a  session
	      name  and	 the  corresponding host and port, in that order (note
	      the session name comes first, not	 last),	 separated  by	white‐
	      space.

	      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 listening port can be closed with `ztcp -c fd'.   A
	      call  to	`tcp_open -a fd' will block until a remote TCP connec‐
	      tion is made to port on the local machine.   At  this  point,  a
	      session  is  created  in	the usual way and is largely indistin‐
	      guishable from an active 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 informational 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 interactive, 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 being installed, so data must be read
	      explicitly.  Note, however, this is not necessary 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 ses‐
	      sion  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 sessions 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 current session, even if there are other ses‐
	      sions 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 option -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 ses‐
	      sions if the option -a is given.	 Any  of  the  -u,  -l	or  -s
	      options may be repeated or mixed together.  The -u option speci‐
	      fies a file descriptor directly (only those managed by this sys‐
	      tem 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 wait‐
	      ing for new data.	 Any one line of data from any of  the	avail‐
	      able  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 func‐
	      tion will block until 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-exis‐
	      tent 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 underlying operation differs little from a `print -r'
	      to the session's file descriptor, although it attempts  to  pre‐
	      vent  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 input 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 affected.

	      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 created empty.	 With no argu‐
	      ments, 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  ... ] ]
	      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	conve‐
	      nient; 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	the string command ....	 The first argument is
	      re-evaluated so as to expand aliases  etc.,  but	the  remaining
	      arguments	 are  passed  through  as the appear to tcp_sess.  The
	      original session is restored when tcp_sess exits.

   Advanced I/O
       tcp_command send-options ... send-arguments ...
	      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 cur‐
	      rent 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 con‐
	      nection.	Within a programme or function it is generally	better
	      to handle reading data by a more explicit method.

       tcp_expect [ -q ] [ -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 sessions.  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 current 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 immedi‐
	      ately 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  backreferences  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,
	      respectively, in seconds, as an integer or  floating-point  num‐
	      ber.   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 return, $var  is  set
	      to  the  number of the pattern using ordinary zsh indexing, i.e.
	      the first is 1, and so on.  Note the absence of a `$'  in	 front
	      of  var.	 To  avoid  clashes,  the  parameter cannot begin with
	      `_expect'.

	      The 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  whatso‐
	      ever  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 lis‐
	      ten.

	      The remaining arguments give a command and its arguments to exe‐
	      cute 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 ...
	      Execute `cmd ...' 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 ses‐
	      sions.

	      Normally, any sessions added by the `-a' flag or when  all  ses‐
	      sions  are  chosen  implicitly  are spammed in alphabetic order;
	      sessions given by the $tcp_spam_list array  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  function  described	below.
	      (Obviously that function is able to generate its own output.)

	      If  the  option -e is present, the line given as cmd ... is exe‐
	      cuted 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_SESSION.

	      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 edi‐
	      tor'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 func‐
       tion system in certain contexts.	 This facility depends on  the	module
       zsh/parameter,  which is usually available 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 reus‐
	      able, by default it removes it from the list of file descriptors
	      handled  by  this	 method and prints a message.  If the function
	      tcp_on_awol is defined it	 is  called  immediately  before  this
	      point.   It may return status 100, which indicates that the nor‐
	      mal handling should still be performed; 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 ses‐
	      sion.

	      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 session name, file descriptor, new session name.

       tcp_on_spam sess command ...
	      This is called once for each session spammed, just before a com‐
	      mand  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 func‐
	      tion.   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 executed; 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 descriptor 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 contain:
	      %c     Expands  to 1 if the session is the current session, oth‐
		     erwise  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 associa‐
       tive 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	 func‐
       tion.   For example, `local TCP_SILENT=1' specifies that data read dur‐
       ing the function call will not be printed to standard  output,  regard‐
       less   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 patterns 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 `%', respec‐
	      tively.  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
	      session is the current one, else `-'.

       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 established 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	 func‐
	      tion 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	 func‐
	      tion 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	 argu‐
	      ments: 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  sta‐
	      tus,  the	 line  is not output.  Thus a tcp_on_read handler con‐
	      taining 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	estab‐
	      lished  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 descriptor 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 infuriating 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 out‐
       put (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 connections 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 new‐
       line can cause the function to block indefinitely.

       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.

zsh 4.3.17		       February 22, 2011		  ZSHTCPSYS(1)
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