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ZSHTCPSYS(1)                                                      ZSHTCPSYS(1)



NAME
       zshtcpsys - zsh tcp system

DESCRIPTION
       A  module zsh/net/tcp is provided to provide network I/O over TCP/IP from within the shell; see its description
       in zshmodules(1) .  This manual page describes a function  suite  based  on  the  module.   If  the  module  is
       installed,  the  functions  are  usually  installed  at the same time, in which case they will be available for
       autoloading in the default function search path.  In addition to the zsh/net/tcp module, the zsh/zselect module
       is  used  to implement timeouts on read 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 doc-
       umented 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  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 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  sta-
              tus 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 man-
              ner 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 ses-
              sion 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 cur-
              rent status of logging.

              With  the  option  -s,  per-session  logging is enabled.  Input from tcp_read is output to the file log-
              file.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  out-
              put; hence 'tcp_log -cn' turns off all output by tcp_read.

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

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

       tcp_sess [ sess [ command  ... ] ]
              With no arguments, list all the open sessions and associated file descriptors.  The current  session  is
              marked  with a star.  For use in functions, direct access to the parameters $tcp_by_name, $tcp_by_fd and
              $TCP_SESS is probably more 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 match-
              ing  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  backrefer-
              ences  available  in  the parameters $MATCH, $match, etc., as described in the base zsh documentation on
              pattern matching.

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

              The  function returns as soon as any one of the patterns given match.  If the caller needs to know which
              of the patterns matched, the option -p var can be used; on return, $var is set to the number of the pat-
              tern using ordinary zsh indexing, i.e. the first is 1, and so on.  Note the absence of a '$' in front of
              var.  To avoid clashes, the parameter cannot begin with '_expect'.

              The option -q is passed directly down to tcp_read.

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

       tcp_proxy
              This is a simple-minded function to accept a TCP connection and execute a command with I/O redirected to
              the  connection.   Extreme caution should be taken as there is no security 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 ...
              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 implic-
              itly.  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 ... 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_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 rea-
              son, many users will prefer to use some form of alternative approach for sending data easily to the cur-
              rent 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  comple-
       tion  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 descrip-
              tor  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 per-
              formed; any other return status indicates that no further action should be taken and the  tcp_fd_handler
              should  return  immediately with the given status.  Typically the action of tcp_on_awol will be to close
              the session.

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

              ('AWOL' is military jargon for 'absent without leave' or some variation.  It has no pre-existing techni-
              cal 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 argu-
              ments.  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 descrip-
              tor, 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 correspond-
              ing 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 '%', respec-
              tively.  The expression '%c' expands to 1 if the session being read is the current session, else 0; this
              is most useful in ternary expressions such as '%(c.-.+)' which outputs '+' if the session is the current
              one, else '-'.

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

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

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

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

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

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

       tcp_spam_list
              Array.  May be set directly.  See the description of the 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 partic-
              ular  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 arriv-
       ing 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  perfor-
       mance when large amounts of data are being exchanged is likely to be extremely poor.



zsh 4.3.11                     December 20, 2010                  ZSHTCPSYS(1)