ZSHTCPSYS(1)

📦
version 5.9.2 · 5 versions
, in arch rolling, nixpkgs unstable

✨ NAME ✨

zshtcpsys — the zsh tcp system 🦋

(and yes, this is the ZSHTCPSYS(1) page from General Commands Manual, bestie — buckle up 💖)

🌸 DESCRIPTION 🌸

okay so first things first: there's this module called zsh/net/tcp, and it's the whole reason we can do network I/O over TCP/IP from inside the shell — like, straight up, no leaving home. the full rundown of the module itself lives in zshmodules(1). this page, though? this page is about the function suite that's built on top of it. 🎀

so if the module is installed, the functions usually get installed right alongside it, which means they'll be sitting there ready for autoloading in the default function search path. and it's not just the zsh/net/tcp module doing the work — the zsh/zselect module also gets pulled in, because that's what makes timeouts on read operations possible. if you're in troubleshooting mode, go consult the matching advice for the zftp functions over in zshzftpsys(1). 💅

there are functions that mirror the basic I/O operations — open, close, read and send — named tcp_open etc., plus a tcp_expect function for doing pattern match analysis on the data you read in. and the way this whole system works makes it easy to receive data from and send data to multiple named sessions at the same time, which is lowkey iconic. ✨ on top of that, it can be linked with the shell's line editor so input data gets automatically shown at the terminal. other facilities include logging, filtering, and configurable output prompts. we love a feature-rich queen. 👑

to get started where it's available, honestly it should be enough to autoload -U tcp_open and then just run tcp_open as documented below to start a session. tcp_open will autoload the remaining functions for you. no cap. 🫶

🔥 TCP USER FUNCTIONS 🔥

💖 Basic I/O 💖

tcp_open

tcp_open [ -qz ] host port [ sess ]
tcp_open [ -qz ] [ -s sess | -l sess[,...] ] ...
tcp_open [ -qz ] [ -a fd | -f fd ] [ sess ]

opens a new session, periodt. 🌈

first form (the simplest one): open a TCP connection to host at port. both numeric and symbolic forms are understood, so you can go either way, bestie. 💅

if sess is given, that becomes the name of the session — and that's what you'll use to refer to multiple different TCP connections. if sess isn't given, the function just invents a numeric name value for you (and heads up: that name is not the same as the file descriptor the session is attached to, so don't get it twisted 🙈). also, please don't put "funny" characters in your session names. and yeah, "funny" is not well-defined, but it certainly does not include alphanumerics or underscores, and it certainly does include whitespace. so like... keep it cute and boring. 🎀

second form: one or more sessions to be opened are given by name. a single session name goes after -s, and a comma-separated list goes after -l; both options can be repeated as many times as you need. ⭐ if any session fails to open, tcp_open aborts — no half-finished nonsense. the host and port get read from the file .ztcp_sessions, which lives in the same directory as the user's zsh initialisation files — so usually the home directory, but $ZDOTDIR if that's set. 💜 the file is made of lines, each giving a session name and the corresponding host and port, in that order (yes, the session name comes first, not last — read it again, i said what i said), all separated by whitespace.

third form: this is where passive and fake TCP connections come in. 🦋

  • if the option -a is used, its argument is a file descriptor that's open for listening for connections. there's no function front-end 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 that point a session gets created in the usual way, and it's largely indistinguishable from an active connection created with one of the first two forms. slay. 💅
  • if the option -f is used, its argument is a file descriptor that gets used directly, as if it were a TCP session. how well the rest of the TCP function system copes with this depends entirely on what actually underlies that 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. you've been warned, bestie. 😭

if the option -q is given with any of the three forms, tcp_open will not print informational messages — though 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 that checks for new data at the same time as it checks for keyboard input. this is convenient because 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, because zle is not active at that 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 the system uses. 💖

the function tcp_on_open, if defined, is called when a session is opened. see the description below. ✨

tcp_close

tcp_close [ -qn ] [ -a | -l sess[,...] | sess ... ]

closes 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 gets unset, leaving no current session — even if there are other sessions still open. so yeah, you can end up session-less. it's giving orphaned. 😭

if the session was opened with tcp_open -f, the file descriptor is closed so long as it's 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. and heads up: the -n option is not used for genuine ztcp sessions — the file descriptors are always closed with the session. 💅

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

tcp_read

tcp_read [ -bdq ] [ -t TO ] [ -T TO ]
         [ -a | -u fd[,...] | -l sess[,...] | -s sess ... ]

performs a read operation on the current session — or on a list of sessions if any are given with -u, -l or -s, or on 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), and the other two specify sessions exactly 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 gets 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 is shown at the start of the line; the default form for this includes the name of the session being read. ✨ see below for more info 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 — and this is important — only a single line is returned. one. uno. 🎀

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 array 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

tcp_send [ -cnq ] [ -s sess | -l sess[,...] ] data ...
tcp_send [ -cnq ] -a data ...

sends the supplied data strings to all the specified sessions, in turn. 🌈 the underlying operation differs very little from a print -r to the session's file descriptor — although it does attempt to prevent the shell from dying owing to a SIGPIPE caused by an attempt to write to a defunct session. so like, it's got your back. 💀

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 exactly as for tcp_read. 🎀

the data arguments are not further processed once they've been passed to tcp_send; they're simply passed down to print -r. no extra seasoning. 🧂

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

tcp_alias [ -q ] alias=sess ...
tcp_alias [ -q ] [ alias ... ]
tcp_alias -d [ -q ] alias ...

this function is not particularly well tested. 🙈💀

(more coming, bestie — this is only part one 🫶)

okay so the first form creates an alias for a session name; then alias can be used to refer to the existing session sess. You can list as many aliases as you need, bestie. The second form lists any aliases you name, or all aliases if you name none. The third form deletes all the aliases listed. The underlying sessions are not affected. The -q option suppresses an inconsistently chosen subset of error messages — yes, that is literally the brief, and no I did not make it up.

🧚 tcp_log [ -asc ] [ -n | -N ] [ logfile ]

With a logfile argument, all future input from tcp_read gets logged to that named file. Unless -a (append) is given, the file is first truncated or created empty. With no arguments, it shows the current status of logging.

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

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

The -n and -N options 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 they 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

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.

bestie please hear me: no security whatsoever. firewall only. this is not a drill. 🚨

🎀 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 at.

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

Okay, tiny carry-over from the last bit: because these two functions don’t need tcp_open to set up a TCP connection first, they may need to be autoloaded separately. 🫶

✨ TCP USER-DEFINED FUNCTIONS ✨

So here’s the vibe: some functions, if you define them yourself, get called by the function system in certain contexts. This whole facility depends on the module zsh/parameter, which is usually available in interactive shells because the completion system depends on it. None of these functions have to be defined — they’re just convenient hooks when you need them. 👑

Typically, they’re called after the requested action has already happened, so the various parameters reflect the new state. Slay.

tcp_on_alias alias fd

When an alias is defined, this function gets 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. Like, they’re backstage crew — iconic, but you’re probably not grabbing the mic. 🎤

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 it 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 ✨

Okay so these follow the usual convention, bestie: uppercase = scalars and integers, lowercase = normal and associative arrays. 🎀

It is always safe for user code to read these parameters. Some of them may also be set — those are noted explicitly. The rest are hanging out in this group because the function system sets them for your benefit, i.e. setting them is typically not useful, but it's benign. 💅

It's often also super 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. Obsessed with the scoping honestly. 🫶

  • tcp_expect_lines — Array. The set of lines read during the last call to tcp_expect, including the last one ($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 a 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. Your current fave line, basically. ✨
  • 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 one ($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 preceded 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. 😭 math but make it shell

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. The main character session, if you will. 👑
  • 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 they have a special effect if set by the user. You're in charge here, bestie. 💖

  • 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. Look with your eyes, not with your hands, okay? 🙈

  • 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. Iconic, lowkey. ✨

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. 💀 rude but true

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. 😭 no cap, it'll just sit there

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. ngl, fr fr — big data? not her thing.

That's the whole page, bestie! 🎀 This was zsh version 5.9.2, dated July 12, 2026 — go forth and talk to sockets, you absolute icon. 💅✨🫶

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