ZSHTCPSYS(1)



ZSHTCPSYS(1)                General Commands Manual               ZSHTCPSYS(1)

NAME
       zshtcpsys - zsh tcp system

DESCRIPTION
       A  module  zsh/net/tcp  is  provided to provide network I/O over TCP/IP
       from within the shell; see its description in zshmodules(1).  This man-
       ual 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 func-
       tion search path.  In addition to the zsh/net/tcp module, the  zsh/zse-
       lect  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 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  `au-
       toload  -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  un-
              derscores, 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 $RE-
              PLY.  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 un-
              set,  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 di-
              rectly from the command line.  If the option -n is given, no at-
              tempt  will be made to close file descriptors in this case.  The
              -n option is not used for genuine ztcp  session;  the  file  de-
              scriptors 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  op-
              tions  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 re-
              turned.

              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  op-
              tion, 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 at-
              tempt 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  er-
              ror 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 pa-
              rameters  $TCP_LOG,  $TCP_LOG_SESS,  $TCP_SILENT,  which are de-
              scribed below.

       tcp_rename old new
              Rename session old to session new.  The  old  name  becomes  in-
              valid.

       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  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  `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 re-
              stored 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 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 | -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 pa-
              rameters $MATCH, $match, etc., as described in the base zsh doc-
              umentation on pattern matching.

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

              The  function  returns  as soon as any one of the patterns given
              match.  If the caller  needs  to  know  which  of  the  patterns
              matched,  the  option -p var can be used; on 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 `_ex-
              pect'.   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  numeri-
              cal  indexes the regular arguments must begin with a prefix fol-
              lowed 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.  Ex-
              treme 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 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 ac-
              count, which in many cases will be a bad thing.

              The command is run in the background, so tcp_proxy can then  ac-
              cept  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 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.   (Ob-
              viously 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  al-
              low  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  un-
              used 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  de-
       fined; 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 at-
              tempt 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  in-
              clude  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 `lo-
       cal 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_ex-
              pect, 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 `-'.

              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 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_ex-
              pect) 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  it-
              self.

              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 5.8                        February 14, 2020                  ZSHTCPSYS(1)

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