ZSHTCPSYS(1) User Commands 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 documented below to start
a session. The tcp_open function will autoload the remaining
functions.

TCP USER FUNCTIONS

Basic I/O
tcp_open [ -qz ] host port [ sess ]
tcp_open [ -qz ] [ -s sess | -l sess[,...] ] ...
tcp_open [ -qz ] [ -a fd | -f fd ] [ sess ]
Open a new session. In the first and simplest form, open a
TCP connection to host host at port port; numeric and symbolic
forms are understood for both.

If sess is given, this becomes the name of the session which
can be used to refer to multiple different TCP connections.
If sess is not given, the function will invent a numeric name
value (note this is not the same as the file descriptor to
which the session is attached). It is recommended that
session names not include `funny' characters, where funny
characters are not well-defined but certainly do not include
alphanumerics or underscores, and certainly do include
whitespace.

In the second case, one or more sessions to be opened are
given by name. A single session name is given after -s and a
comma-separated list after -l; both options may be repeated as
many times as necessary. A failure to open any session causes
tcp_open to abort. The host and port are read from the file
.ztcp_sessions in the same directory as the user's zsh
initialisation files, i.e. usually the home directory, but
$ZDOTDIR if that is set. The file consists of lines each
giving a session name and the corresponding host and port, in
that order (note the session name comes first, not last),
separated by whitespace.

The third form allows passive and fake TCP connections. If
the option -a is used, its argument is a file descriptor open
for listening for connections. No function front-end is
provided to open such a file descriptor, but a call to `ztcp
-l port' will create one with the file descriptor stored in
the parameter $REPLY. The listening port can be closed with
`ztcp -c fd'. A call to `tcp_open -a fd' will block until a
remote TCP connection is made to port on the local machine.
At this point, a session is created in the usual way and is
largely indistinguishable from an active connection created
with one of the first two forms.

If the option -f is used, its argument is a file descriptor
which is used directly as if it were a TCP session. How well
the remainder of the TCP function system copes with this
depends on what actually underlies this file descriptor. A
regular file is likely to be unusable; a FIFO (pipe) of some
sort will work better, but note that it is not a good idea for
two different sessions to attempt to read from the same FIFO
at once.

If the option -q is given with any of the three forms,
tcp_open will not print informational messages, although it
will in any case exit with an appropriate status.

If the line editor (zle) is in use, which is typically the
case if the shell is interactive, tcp_open installs a handler
inside zle which will check for new data at the same time as
it checks for keyboard input. This is convenient as the shell
consumes no CPU time while waiting; the test is performed by
the operating system. Giving the option -z to any of the
forms of tcp_open prevents the handler from being installed,
so data must be read explicitly. Note, however, this is not
necessary for executing complete sets of send and read
commands from a function, as zle is not active at this point.
Generally speaking, the handler is only active when the shell
is waiting for input at a command prompt or in the vared
builtin. The option has no effect if zle is not active; `[[
-o zle]]' will test for this.

The first session to be opened becomes the current session and
subsequent calls to tcp_open do not change it. The current
session is stored in the parameter $TCP_SESS; see below for
more detail about the parameters used by the system.

The function tcp_on_open, if defined, is called when a session
is opened. See the description below.

tcp_close [ -qn ] [ -a | -l sess[,...] | sess ... ]
Close the named sessions, or the current session if none is
given, or all open sessions if -a is given. The options -l
and -s are both handled for consistency with tcp_open,
although the latter is redundant.

If the session being closed is the current one, $TCP_SESS is
unset, leaving no current session, even if there are other
sessions still open.

If the session was opened with tcp_open -f, the file
descriptor is closed so long as it is in the range 0 to 9
accessible directly from the command line. If the option -n
is given, no attempt will be made to close file descriptors in
this case. The -n option is not used for genuine ztcp
session; the file descriptors are always closed with the
session.

If the option -q is given, no informational messages will be
printed.


tcp_read [ -bdq ] [ -t TO ] [ -T TO ]
[ -a | -u fd[,...] | -l sess[,...] | -s sess ... ]
Perform a read operation on the current session, or on a list
of sessions if any are given with -u, -l or -s, or all open
sessions if the option -a is given. Any of the -u, -l or -s
options may be repeated or mixed together. The -u option
specifies a file descriptor directly (only those managed by
this system are useful), the other two specify sessions as
described for tcp_open above.

The function checks for new data available on all the sessions
listed. Unless the -b option is given, it will not block
waiting for new data. Any one line of data from any of the
available sessions will be read, stored in the parameter
$TCP_LINE, and displayed to standard output unless $TCP_SILENT
contains a non-empty string. When printed to standard output
the string $TCP_PROMPT will be shown at the start of the line;
the default form for this includes the name of the session
being read. See below for more information on these
parameters. In this mode, tcp_read can be called repeatedly
until it returns status 2 which indicates all pending input
from all specified sessions has been handled.

With the option -b, equivalent to an infinite timeout, the
function will block until a line is available to read from one
of the specified sessions. However, only a single line is
returned.

The option -d indicates that all pending input should be
drained. In this case tcp_read may process multiple lines in
the manner given above; only the last is stored in $TCP_LINE,
but the complete set is stored in the array $tcp_lines. This
is cleared at the start of each call to tcp_read.

The options -t and -T specify a timeout in seconds, which may
be a floating point number for increased accuracy. With -t
the timeout is applied before each line read. With -T, the
timeout applies to the overall operation, possibly including
multiple read operations if the option -d is present; without
this option, there is no distinction between -t and -T.

The function does not print informational messages, but if the
option -q is given, no error message is printed for a
non-existent session.

A return status of 2 indicates a timeout or no data to read.
Any other non-zero return status indicates some error
condition.

See tcp_log for how to control where data is sent by tcp_read.

tcp_send [ -cnq ] [ -s sess | -l sess[,...] ] data ...
tcp_send [ -cnq ] -a data ...
Send the supplied data strings to all the specified sessions
in turn. The underlying operation differs little from a
`print -r' to the session's file descriptor, although it
attempts to prevent the shell from dying owing to a SIGPIPE
caused by an attempt to write to a defunct session.

The option -c causes tcp_send to behave like cat. It reads
lines from standard input until end of input and sends them in
turn to the specified session(s) exactly as if they were given
as data arguments to individual tcp_send commands.

The option -n prevents tcp_send from putting a newline at the
end of the data strings.

The remaining options all behave as for tcp_read.

The data arguments are not further processed once they have
been passed to tcp_send; they are simply passed down to print
-r.

If the parameter $TCP_OUTPUT is a non-empty string and logging
is enabled then the data sent to each session will be echoed
to the log file(s) with $TCP_OUTPUT in front where
appropriate, much in the manner of $TCP_PROMPT.

Session Management

tcp_alias [ -q ] alias=sess ...
tcp_alias [ -q ] [ alias ... ]
tcp_alias -d [ -q ] alias ...
This function is not particularly well tested.

The first form creates an alias for a session name; alias can
then be used to refer to the existing session sess. As many
aliases may be listed as required.

The second form lists any aliases specified, or all aliases if
none.

The third form deletes all the aliases listed. The underlying
sessions are not affected.

The option -q suppresses an inconsistently chosen subset of
error messages.

tcp_log [ -asc ] [ -n | -N ] [ logfile ]
With an argument logfile, all future input from tcp_read will
be logged to the named file. Unless -a (append) is given,
this file will first be truncated or created empty. With no
arguments, show the current status of logging.

With the option -s, per-session logging is enabled. Input
from tcp_read is output to the file logfile.sess. As the
session is automatically discriminated by the filename, the
contents are raw (no $TCP_PROMPT). The option -a applies as
above. Per-session logging and logging of all data in one
file are not mutually exclusive.

The option -c closes all logging, both complete and
per-session logs.

The options -n and -N respectively turn off or restore output
of data read by tcp_read to standard output; hence `tcp_log
-cn' turns off all output by tcp_read.

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

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

tcp_sess [ sess [ command [ arg ... ] ] ]
With no arguments, list all the open sessions and associated
file descriptors. The current session is marked with a star.
For use in functions, direct access to the parameters
$tcp_by_name, $tcp_by_fd and $TCP_SESS is probably more
convenient; see below.

With a sess argument, set the current session to sess. This
is equivalent to changing $TCP_SESS directly.

With additional arguments, temporarily set the current session
while executing `command arg ...'. command is re-evaluated so
as to expand aliases etc., but the remaining args are passed
through as that appear to tcp_sess. The original session is
restored when tcp_sess exits.

Advanced I/O
tcp_command send-option ... send-argument ...
This is a convenient front-end to tcp_send. All arguments are
passed to tcp_send, then the function pauses waiting for data.
While data is arriving at least every $TCP_TIMEOUT (default
0.3) seconds, data is handled and printed out according to the
current settings. Status 0 is always returned.

This is generally only useful for interactive use, to prevent
the display becoming fragmented by output returned from the
connection. Within a programme or function it is generally
better to handle reading data by a more explicit method.


tcp_expect [ -q ] [ -p var | -P var ] [ -t TO | -T TO ]
[ -a | -s sess | -l sess[,...] ] pattern ...
Wait for input matching any of the given patterns from any of
the specified sessions. Input is ignored until an input line
matches one of the given patterns; at this point status zero
is returned, the matching line is stored in $TCP_LINE, and the
full set of lines read during the call to tcp_expect is stored
in the array $tcp_expect_lines.

Sessions are specified in the same way as tcp_read: the
default is to use the current session, otherwise the sessions
specified by -a, -s, or -l are used.

Each pattern is a standard zsh extended-globbing pattern; note
that it needs to be quoted to avoid it being expanded
immediately by filename generation. It must match the full
line, so to match a substring there must be a `*' at the start
and end. The line matched against includes the $TCP_PROMPT
added by tcp_read. It is possible to include the globbing
flags `#b' or `#m' in the patterns to make backreferences
available in the parameters $MATCH, $match, etc., as described
in the base zsh documentation on pattern matching.

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

The function returns as soon as any one of the patterns given
match. If the caller needs to know which of the patterns
matched, the option -p var can be used; on return, $var is set
to the number of the pattern using ordinary zsh indexing, i.e.
the first is 1, and so on. Note the absence of a `$' in front
of var. To avoid clashes, the parameter cannot begin with
`_expect'. The index -1 is used if there is a timeout and 0
if there is no match.

The option -P var works similarly to -p, but instead of
numerical indexes the regular arguments must begin with a
prefix followed by a colon: that prefix is then used as a tag
to which var is set when the argument matches. The tag
timeout is used if there is a timeout and the empty string if
there is no match. Note it is acceptable for different
arguments to start with the same prefix if the matches do not
need to be distinguished.

The option -q is passed directly down to tcp_read.

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

tcp_proxy
This is a simple-minded function to accept a TCP connection
and execute a command with I/O redirected to the connection.
Extreme caution should be taken as there is no security
whatsoever and this can leave your computer open to the world.
Ideally, it should only be used behind a firewall.

The first argument is a TCP port on which the function will
listen.

The remaining arguments give a command and its arguments to
execute with standard input, standard output and standard
error redirected to the file descriptor on which the TCP
session has been accepted. If no command is given, a new zsh
is started. This gives everyone on your network direct access
to your account, which in many cases will be a bad thing.

The command is run in the background, so tcp_proxy can then
accept new connections. It continues to accept new
connections until interrupted.

tcp_spam [ -ertv ] [ -a | -s sess | -l sess[,...] ] cmd [ arg ... ]
Execute `cmd [ arg ... ]' for each session in turn. Note this
executes the command and arguments; it does not send the
command line as data unless the -t (transmit) option is given.

The sessions may be selected explicitly with the standard -a,
-s or -l options, or may be chosen implicitly. If none of the
three options is given the rules are: first, if the array
$tcp_spam_list is set, this is taken as the list of sessions,
otherwise all sessions are taken. Second, any sessions given
in the array $tcp_no_spam_list are removed from the list of
sessions.

Normally, any sessions added by the `-a' flag or when all
sessions are chosen implicitly are spammed in alphabetic
order; sessions given by the $tcp_spam_list array or on the
command line are spammed in the order given. The -r flag
reverses the order however it was arrived it.

The -v flag specifies that a $TCP_PROMPT will be output before
each session. This is output after any modification to
TCP_SESS by the user-defined tcp_on_spam function described
below. (Obviously that function is able to generate its own
output.)

If the option -e is present, the line given as `cmd [ arg ...
]' is executed using eval, otherwise it is executed without
any further processing.

tcp_talk
This is a fairly simple-minded attempt to force input to the
line editor to go straight to the default TCP_SESS.

An escape string, $TCP_TALK_ESCAPE, default `:', is used to
allow access to normal shell operation. If it is on its own
at the start of the line, or followed only by whitespace, the
line editor returns to normal operation. Otherwise, the
string and any following whitespace are skipped and the
remainder of the line executed as shell input without any
change of the line editor's operating mode.

The current implementation is somewhat deficient in terms of
use of the command history. For this reason, many users will
prefer to use some form of alternative approach for sending
data easily to the current session. One simple approach is to
alias some special character (such as `%') to `tcp_command
--'.

tcp_wait
The sole argument is an integer or floating point number which
gives the seconds to delay. The shell will do nothing for
that period except wait for input on all TCP sessions by
calling tcp_read -a. This is similar to the interactive
behaviour at the command prompt when zle handlers are
installed.

`One-shot' file transfer
tcp_point port
tcp_shoot host port
This pair of functions provide a simple way to transfer a file
between two hosts within the shell. Note, however, that bulk
data transfer is currently done using cat. tcp_point reads
any data arriving at port and sends it to standard output;
tcp_shoot connects to port on host and sends its standard
input. Any unused port may be used; the standard mechanism
for picking a port is to think of a random four-digit number
above 1024 until one works.

To transfer a file from host woodcock to host springes, on
springes:

tcp_point 8091 >output_file

and on woodcock:

tcp_shoot springes 8091 <input_file

As these two functions do not require tcp_open to set up a TCP
connection first, they may need to be autoloaded separately.

TCP USER-DEFINED FUNCTIONS
Certain functions, if defined by the user, will be called by the
function system in certain contexts. This facility depends on the
module zsh/parameter, which is usually available in interactive
shells as the completion system depends on it. None of the functions
need be defined; they simply provide convenient hooks when necessary.

Typically, these are called after the requested action has been
taken, so that the various parameters will reflect the new state.

tcp_on_alias alias fd
When an alias is defined, this function will be called with
two arguments: the name of the alias, and the file descriptor
of the corresponding session.

tcp_on_awol sess fd
If the function tcp_fd_handler is handling input from the line
editor and detects that the file descriptor is no longer
reusable, by default it removes it from the list of file
descriptors handled by this method and prints a message. If
the function tcp_on_awol is defined it is called immediately
before this point. It may return status 100, which indicates
that the normal handling should still be performed; any other
return status indicates that no further action should be taken
and the tcp_fd_handler should return immediately with the
given status. Typically the action of tcp_on_awol will be to
close the session.

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

(`AWOL' is military jargon for `absent without leave' or some
variation. It has no pre-existing technical meaning known to
the author.)

tcp_on_close sess fd
This is called with the name of a session being closed and the
file descriptor which corresponded to that session. Both will
be invalid by the time the function is called.

tcp_on_open sess fd
This is called after a new session has been defined with the
session name and file descriptor as arguments. If it returns
a non-zero status, opening the session is assumed to fail and
the session is closed again; however, tcp_open will continue
to attempt to open any remaining sessions given on the command
line.

tcp_on_rename oldsess fd newsess
This is called after a session has been renamed with the three
arguments old session name, file descriptor, new session name.

tcp_on_spam sess command ...
This is called once for each session spammed, just before a
command is executed for a session by tcp_spam. The arguments
are the session name followed by the command list to be
executed. If tcp_spam was called with the option -t, the
first command will be tcp_send.

This function is called after $TCP_SESS is set to reflect the
session to be spammed, but before any use of it is made.
Hence it is possible to alter the value of $TCP_SESS within
this function. For example, the session arguments to tcp_spam
could include extra information to be stripped off and
processed in tcp_on_spam.

If the function sets the parameter $REPLY to `done', the
command line is not executed; in addition, no prompt is
printed for the -v option to tcp_spam.

tcp_on_unalias alias fd
This is called with the name of an alias and the corresponding
session's file descriptor after an alias has been deleted.

TCP UTILITY FUNCTIONS

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

tcp_fd_handler
This is the function installed by tcp_open for handling input
from within the line editor, if that is required. It is in
the format documented for the builtin `zle -F' in zshzle(1) .

While active, the function sets the parameter
TCP_HANDLER_ACTIVE to 1. This allows shell code called
internally (for example, by setting tcp_on_read) to tell if is
being called when the shell is otherwise idle at the editor
prompt.

tcp_output [ -q ] -P prompt -F fd -S sess
This function is used for both logging and handling output to
standard output, from within tcp_read and (if $TCP_OUTPUT is
set) tcp_send.

The prompt to use is specified by -P; the default is the empty
string. It can contain:
%c Expands to 1 if the session is the current session,
otherwise 0. Used with ternary expressions such as
`%(c.-.+)' to output `+' for the current session and
`-' otherwise.

%f Replaced by the session's file descriptor.

%s Replaced by the session name.

%% Replaced by a single `%'.

The option -q suppresses output to standard output, but not to
any log files which are configured.

The -S and -F options are used to pass in the session name and
file descriptor for possible replacement in the prompt.

TCP USER PARAMETERS

Parameters follow the usual convention that uppercase is used for
scalars and integers, while lowercase is used for normal and
associative array. It is always safe for user code to read these
parameters. Some parameters may also be set; these are noted
explicitly. Others are included in this group as they are set by the
function system for the user's benefit, i.e. setting them is
typically not useful but is benign.

It is often also useful to make settable parameters local to a
function. For example, `local TCP_SILENT=1' specifies that data read
during the function call will not be printed to standard output,
regardless of the setting outside the function. Likewise, `local
TCP_SESS=sess' sets a session for the duration of a function, and
`local TCP_PROMPT=' specifies that no prompt is used for input during
the function.

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

tcp_filter
Array. May be set directly. A set of extended globbing
patterns which, if matched in tcp_output, will cause the line
not to be printed to standard output. The patterns should be
defined as described for the arguments to tcp_expect. Output
of line to log files is not affected.

TCP_HANDLER_ACTIVE
Scalar. Set to 1 within tcp_fd_handler to indicate to
functions called recursively that they have been called during
an editor session. Otherwise unset.

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

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

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

TCP_LOG
May be set directly, although it is also controlled by
tcp_log. The name of a file to which output from all sessions
will be sent. The output is proceeded by the usual
$TCP_PROMPT. If it is not an absolute path name, it will
follow the user's current directory.

TCP_LOG_SESS
May be set directly, although it is also controlled by
tcp_log. The prefix for a set of files to which output from
each session separately will be sent; the full filename is
${TCP_LOG_SESS}.sess. Output to each file is raw; no prompt
is added. If it is not an absolute path name, it will follow
the user's current directory.

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

TCP_OUTPUT
May be set directly. If a non-empty string, any data sent to
a session by tcp_send will be logged. This parameter gives
the prompt to be used in a file specified by $TCP_LOG but not
in a file generated from $TCP_LOG_SESS. The prompt string has
the same format as TCP_PROMPT and the same rules for its use
apply.

TCP_PROMPT
May be set directly. Used as the prefix for data read by
tcp_read which is printed to standard output or to the log
file given by $TCP_LOG, if any. Any `%s', `%f' or `%%'
occurring in the string will be replaced by the name of the
session, the session's underlying file descriptor, or a single
`%', respectively. The expression `%c' expands to 1 if the
session being read is the current session, else 0; this is
most useful in ternary expressions such as `%(c.-.+)' which
outputs `+' if the session is the current one, else `-'.

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

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

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

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

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

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

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

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

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

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

TCP USER-DEFINED PARAMETERS
The following parameters are not set by the function system, but have
a special effect if set by the user.

tcp_on_read
This should be an associative array; if it is not, the
behaviour is undefined. Each key is the name of a shell
function or other command, and the corresponding value is a
shell pattern (using EXTENDED_GLOB). Every line read from a
TCP session directly or indirectly using tcp_read (which
includes lines read by tcp_expect) is compared against the
pattern. If the line matches, the command given in the key is
called with two arguments: the name of the session from which
the line was read, and the line itself.

If any function called to handle a line returns a non-zero
status, the line is not output. Thus a tcp_on_read handler
containing only the instruction `return 1' can be used to
suppress output of particular lines (see, however, tcp_filter
above). However, the line is still stored in TCP_LINE and
tcp_lines; this occurs after all tcp_on_read processing.

TCP UTILITY PARAMETERS

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

tcp_aliases
Associative array. The keys are the names of sessions
established with tcp_open; each value is a space-separated
list of aliases which refer to that session.

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

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

TCP EXAMPLES

Here is a trivial example using a remote calculator.

To create a calculator server on port 7337 (see the dc manual page
for quite how infuriating the underlying command is):

tcp_proxy 7337 dc

To connect to this from the same host with a session also named `dc':

tcp_open localhost 7337 dc

To send a command to the remote session and wait a short while for
output (assuming dc is the current session):

tcp_command 2 4 + p

To close the session:

tcp_close

The tcp_proxy needs to be killed to be stopped. Note this will not
usually kill any connections which have already been accepted, and
also that the port is not immediately available for reuse.

The following chunk of code puts a list of sessions into an xterm
header, with the current session followed by a star.

print -n "\033]2;TCP:" ${(k)tcp_by_name:/$TCP_SESS/$TCP_SESS\*} "\a"

TCP BUGS

The function tcp_read uses the shell's normal read builtin. As this
reads a complete line at once, data arriving without a terminating
newline can cause the function to block indefinitely.

Though the function suite works well for interactive use and for data
arriving in small amounts, the performance when large amounts of data
are being exchanged is likely to be extremely poor.

zsh 5.9 May 14, 2022 ZSHTCPSYS(1)