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       zshtcpsys - zsh tcp system


       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.


   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

       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

              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

              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

              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

       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
              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  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
              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 ] [ -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

              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

              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.

              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

              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 ...
              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

              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 ... is
              executed using  eval,  otherwise  it  is  executed  without  any
              further processing.

              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
              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 --'.

              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

                     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.


       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

              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

       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

              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.


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

              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 `-'

              %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.


       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.

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

              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.

              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.

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

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

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

              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

              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.

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

              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.

              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 `-'.

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

              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.

              May  be set directly.  The current session; must refer to one of
              the sessions established by tcp_open.

              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.

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

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

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


       The following parameters are not set by the function system, but have a
       special effect if set by the user.

              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.


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

              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.

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

              Associative  array.   The  keys  are the names of sessions; each
              value is the file descriptor associated with that session.


       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:


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


       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.

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