Provided by: zsh-common_5.5.1-1ubuntu2_all bug

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  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
              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  initialisation  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 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
              listening  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 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  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
              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 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
              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 sessions if the option -a is given.  Any
              of the -u, -l or -s options may be repeated  or  mixed  together.   The  -u  option
              specifies  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
              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-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
              underlying 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
              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 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
              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 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
              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 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
              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 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
              regular 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.
              Ideally, 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
              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 [ 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
       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 reusable, 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  normal  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 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
              session 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
              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, 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
              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
              session'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 session is the current one, else `-'.

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

       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 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
              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 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
       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 newline 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.