ZSHTCPSYS(1)ZSHTCPSYS(1)NAMEzshtcpsys - zsh tcp system
DESCRIPTION
A module zsh/net/tcp is provided to provide network I/O over TCP/IP
from within the shell; see its description in zshmodules(1). This man‐
ual page describes a function suite based on the module. If the module
is installed, the functions are usually installed at the same time, in
which case they will be available for autoloading in the default func‐
tion search path. In addition to the zsh/net/tcp module, the zsh/zse‐
lect module is used to implement timeouts on read operations. For
troubleshooting tips, consult the corresponding advice for the zftp
functions described in zshzftpsys(1).
There are functions corresponding to the basic I/O operations open,
close, read and send, named tcp_open etc., as well as a function
tcp_expect for pattern match analysis of data read as input. The sys‐
tem makes it easy to receive data from and send data to multiple named
sessions at once. In addition, it can be linked with the shell's line
editor in such a way that input data is automatically shown at the ter‐
minal. Other facilities available including logging, filtering and
configurable output prompts.
To use the system where it is available, it should be enough to
`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 initiali‐
sation files, i.e. usually the home directory, but $ZDOTDIR if
that is set. The file consists of lines each giving a session
name and the corresponding host and port, in that order (note
the session name comes first, not last), separated by white‐
space.
The third form allows passive and fake TCP connections. If the
option -a is used, its argument is a file descriptor open for
listening for connections. No function front-end is provided to
open such a file descriptor, but a call to `ztcp -l port' will
create one with the file descriptor stored in the parameter
$REPLY. The listening port can be closed with `ztcp -c fd'. A
call to `tcp_open -a fd' will block until a remote TCP connec‐
tion is made to port on the local machine. At this point, a
session is created in the usual way and is largely indistin‐
guishable from an active connection created with one of the
first two forms.
If the option -f is used, its argument is a file descriptor
which is used directly as if it were a TCP session. How well
the remainder of the TCP function system copes with this depends
on what actually underlies this file descriptor. A regular file
is likely to be unusable; a FIFO (pipe) of some sort will work
better, but note that it is not a good idea for two different
sessions to attempt to read from the same FIFO at once.
If the option -q is given with any of the three forms, tcp_open
will not print informational messages, although it will in any
case exit with an appropriate status.
If the line editor (zle) is in use, which is typically the case
if the shell is interactive, tcp_open installs a handler inside
zle which will check for new data at the same time as it checks
for keyboard input. This is convenient as the shell consumes no
CPU time while waiting; the test is performed by the operating
system. Giving the option -z to any of the forms of tcp_open
prevents the handler from being installed, so data must be read
explicitly. Note, however, this is not necessary for executing
complete sets of send and read commands from a function, as zle
is not active at this point. Generally speaking, the handler is
only active when the shell is waiting for input at a command
prompt or in the vared builtin. The option has no effect if zle
is not active; `[[ -o zle]]' will test for this.
The first session to be opened becomes the current session and
subsequent calls to tcp_open do not change it. The current ses‐
sion is stored in the parameter $TCP_SESS; see below for more
detail about the parameters used by the system.
The function tcp_on_open, if defined, is called when a session
is opened. See the description below.
tcp_close [ -qn ] [ -a | -l sess[,...] | sess ... ]
Close the named sessions, or the current session if none is
given, or all open sessions if -a is given. The options -l and
-s are both handled for consistency with tcp_open, although the
latter is redundant.
If the session being closed is the current one, $TCP_SESS is
unset, leaving no current session, even if there are other ses‐
sions still open.
If the session was opened with tcp_open -f, the file descriptor
is closed so long as it is in the range 0 to 9 accessible
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 ses‐
sions if the option -a is given. Any of the -u, -l or -s
options may be repeated or mixed together. The -u option speci‐
fies a file descriptor directly (only those managed by this sys‐
tem are useful), the other two specify sessions as described for
tcp_open above.
The function checks for new data available on all the sessions
listed. Unless the -b option is given, it will not block wait‐
ing for new data. Any one line of data from any of the avail‐
able sessions will be read, stored in the parameter $TCP_LINE,
and displayed to standard output unless $TCP_SILENT contains a
non-empty string. When printed to standard output the string
$TCP_PROMPT will be shown at the start of the line; the default
form for this includes the name of the session being read. See
below for more information on these parameters. In this mode,
tcp_read can be called repeatedly until it returns status 2
which indicates all pending input from all specified sessions
has been handled.
With the option -b, equivalent to an infinite timeout, the func‐
tion will block until a line is available to read from one of
the specified sessions. However, only a single line is
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-exis‐
tent session.
A return status of 2 indicates a timeout or no data to read.
Any other non-zero return status indicates some error condition.
See tcp_log for how to control where data is sent by tcp_read.
tcp_send [ -cnq ] [ -s sess | -l sess[,...] ] data ...
tcp_send [ -cnq ] -a data ...
Send the supplied data strings to all the specified sessions in
turn. The underlying operation differs little from a `print -r'
to the session's file descriptor, although it attempts to pre‐
vent the shell from dying owing to a SIGPIPE caused by an
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 argu‐
ments, show the current status of logging.
With the option -s, per-session logging is enabled. Input from
tcp_read is output to the file logfile.sess. As the session is
automatically discriminated by the filename, the contents are
raw (no $TCP_PROMPT). The option -a applies as above.
Per-session logging and logging of all data in one file are not
mutually exclusive.
The option -c closes all logging, both complete and per-session
logs.
The options -n and -N respectively turn off or restore output of
data read by tcp_read to standard output; hence `tcp_log -cn'
turns off all output by tcp_read.
The function is purely a convenient front end to setting the
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 conve‐
nient; see below.
With a sess argument, set the current session to sess. This is
equivalent to changing $TCP_SESS directly.
With additional arguments, temporarily set the current session
while executing `command arg ...'. command is re-evaluated so
as to expand aliases etc., but the remaining args are passed
through as that appear to tcp_sess. The original session is
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 cur‐
rent settings. Status 0 is always returned.
This is generally only useful for interactive use, to prevent
the display becoming fragmented by output returned from the con‐
nection. Within a programme or function it is generally better
to handle reading data by a more explicit method.
tcp_expect [ -q ] [ -p var | -P var ] [ -t TO | -T TO ]
[ -a | -s sess | -l sess[,...] ] pattern ...
Wait for input matching any of the given patterns from any of
the specified sessions. Input is ignored until an input line
matches one of the given patterns; at this point status zero is
returned, the matching line is stored in $TCP_LINE, and the full
set of lines read during the call to tcp_expect is stored in the
array $tcp_expect_lines.
Sessions are specified in the same way as tcp_read: the default
is to use the current session, otherwise the sessions specified
by -a, -s, or -l are used.
Each pattern is a standard zsh extended-globbing pattern; note
that it needs to be quoted to avoid it being expanded immedi‐
ately by filename generation. It must match the full line, so
to match a substring there must be a `*' at the start and end.
The line matched against includes the $TCP_PROMPT added by
tcp_read. It is possible to include the globbing flags `#b' or
`#m' in the patterns to make backreferences available in the
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, $var is set
to the number of the pattern using ordinary zsh indexing, i.e.
the first is 1, and so on. Note the absence of a `$' 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 numeri‐
cal indexes the regular arguments must begin with a prefix fol‐
lowed by a colon: that prefix is then used as a tag to which var
is set when the argument matches. The tag timeout is used if
there is a timeout and the empty string if there is no match.
Note it is acceptable for different arguments to start with the
same prefix if the matches do not need to be distinguished.
The option -q is passed directly down to tcp_read.
As all input is done via tcp_read, all the usual rules about
output of lines read apply. One exception is that the parameter
$tcp_lines will only reflect the line actually matched by
tcp_expect; use $tcp_expect_lines for the full set of lines read
during the function call.
tcp_proxy
This is a simple-minded function to accept a TCP connection and
execute a command with I/O redirected to the connection.
Extreme caution should be taken as there is no security whatso‐
ever and this can leave your computer open to the world. Ide‐
ally, it should only be used behind a firewall.
The first argument is a TCP port on which the function will lis‐
ten.
The remaining arguments give a command and its arguments to exe‐
cute with standard input, standard output and standard error
redirected to the file descriptor on which the TCP session has
been accepted. If no command is given, a new zsh is started.
This gives everyone on your network direct access to your
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 ses‐
sions.
Normally, any sessions added by the `-a' flag or when all ses‐
sions are chosen implicitly are spammed in alphabetic order;
sessions given by the $tcp_spam_list array or on the command
line are spammed in the order given. The -r flag reverses the
order however it was arrived it.
The -v flag specifies that a $TCP_PROMPT will be output before
each session. This is output after any modification to TCP_SESS
by the user-defined tcp_on_spam function described below.
(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 edi‐
tor's operating mode.
The current implementation is somewhat deficient in terms of use
of the command history. For this reason, many users will prefer
to use some form of alternative approach for sending data easily
to the current session. One simple approach is to alias some
special character (such as `%') to `tcp_command --'.
tcp_wait
The sole argument is an integer or floating point number which
gives the seconds to delay. The shell will do nothing for that
period except wait for input on all TCP sessions by calling
tcp_read -a. This is similar to the interactive behaviour at
the command prompt when zle handlers are installed.
`One-shot' file transfer
tcp_point port
tcp_shoot host port
This pair of functions provide a simple way to transfer a file
between two hosts within the shell. Note, however, that bulk
data transfer is currently done using cat. tcp_point reads any
data arriving at port and sends it to standard output; tcp_shoot
connects to port on host and sends its standard input. Any
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 func‐
tion system in certain contexts. This facility depends on the module
zsh/parameter, which is usually available in interactive shells as the
completion system depends on it. None of the functions need be
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 reus‐
able, by default it removes it from the list of file descriptors
handled by this method and prints a message. If the function
tcp_on_awol is defined it is called immediately before this
point. It may return status 100, which indicates that the nor‐
mal handling should still be performed; any other return status
indicates that no further action should be taken and the
tcp_fd_handler should return immediately with the given status.
Typically the action of tcp_on_awol will be to close the ses‐
sion.
The variable TCP_INVALIDATE_ZLE will be a non-empty string if it
is necessary to invalidate the line editor display using `zle
-I' before printing output from the function.
(`AWOL' is military jargon for `absent without leave' or some
variation. It has no pre-existing technical meaning known to
the author.)
tcp_on_close sess fd
This is called with the name of a session being closed and the
file descriptor which corresponded to that session. Both will
be invalid by the time the function is called.
tcp_on_open sess fd
This is called after a new session has been defined with the
session name and file descriptor as arguments. If it returns a
non-zero status, opening the session is assumed to fail and the
session is closed again; however, tcp_open will continue to
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 com‐
mand is executed for a session by tcp_spam. The arguments are
the session name followed by the command list to be executed.
If tcp_spam was called with the option -t, the first command
will be tcp_send.
This function is called after $TCP_SESS is set to reflect the
session to be spammed, but before any use of it is made. Hence
it is possible to alter the value of $TCP_SESS within this func‐
tion. For example, the session arguments to tcp_spam could
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 $TCP_OUTPUT is
set) tcp_send.
The prompt to use is specified by -P; the default is the empty
string. It can contain:
%c Expands to 1 if the session is the current session, oth‐
erwise 0. Used with ternary expressions such as
`%(c.-.+)' to output `+' for the current session and `-'
otherwise.
%f Replaced by the session's file descriptor.
%s Replaced by the session name.
%% Replaced by a single `%'.
The option -q suppresses output to standard output, but not to
any log files which are configured.
The -S and -F options are used to pass in the session name and
file descriptor for possible replacement in the prompt.
TCP USER PARAMETERS
Parameters follow the usual convention that uppercase is used for
scalars and integers, while lowercase is used for normal and associa‐
tive array. It is always safe for user code to read these parameters.
Some parameters may also be set; these are noted explicitly. Others
are included in this group as they are set by the function system for
the user's benefit, i.e. setting them is typically not useful but is
benign.
It is often also useful to make settable parameters local to a func‐
tion. For example, `local TCP_SILENT=1' specifies that data read dur‐
ing the function call will not be printed to standard output, regard‐
less of the setting outside the function. Likewise, `local
TCP_SESS=sess' sets a session for the duration of a function, and
`local TCP_PROMPT=' specifies that no prompt is used for input during
the function.
tcp_expect_lines
Array. The set of lines read during the last call to
tcp_expect, including the last ($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 ses‐
sion's underlying file descriptor, or a single `%', respec‐
tively. The expression `%c' expands to 1 if the session being
read is the current session, else 0; this is most useful in
ternary expressions such as `%(c.-.+)' which outputs `+' if the
session is the current one, else `-'.
If the prompt starts with %P, this is stripped and the complete
result of the previous stage is passed through standard prompt
%-style formatting before being output.
TCP_READ_DEBUG
May be set directly. If this has non-zero length, tcp_read will
give some limited diagnostics about data being read.
TCP_SECONDS_START
This value is created and initialised to zero by tcp_open.
The functions tcp_read and tcp_expect use the shell's SECONDS
parameter for their own timing purposes. If that parameter is
not of floating point type on entry to one of the functions, it
will create a local parameter SECONDS which is floating point
and set the parameter TCP_SECONDS_START to the previous value of
$SECONDS. If the parameter is already floating point, it is
used without a local copy being created and TCP_SECONDS_START is
not set. As the global value is zero, the shell elapsed time is
guaranteed to be the sum of $SECONDS and $TCP_SECONDS_START.
This can be avoided by setting SECONDS globally to a floating
point value using `typeset -F SECONDS'; then the TCP functions
will never make a local copy and never set TCP_SECONDS_START to
a non-zero value.
TCP_SESS
May be set directly. The current session; must refer to one of
the sessions established by tcp_open.
TCP_SILENT
May be set directly, although it is also controlled by tcp_log.
If of non-zero length, data read by tcp_read will not be written
to standard output, though may still be written to a log file.
tcp_spam_list
Array. May be set directly. See the description of the func‐
tion tcp_spam for how this is used.
TCP_TALK_ESCAPE
May be set directly. See the description of the function
tcp_talk for how this is used.
TCP_TIMEOUT
May be set directly. Currently this is only used by the func‐
tion tcp_command, see above.
TCP USER-DEFINED PARAMETERS
The following parameters are not set by the function system, but have a
special effect if set by the user.
tcp_on_read
This should be an associative array; if it is not, the behaviour
is undefined. Each key is the name of a shell function or other
command, and the corresponding value is a shell pattern (using
EXTENDED_GLOB). Every line read from a TCP session directly or
indirectly using tcp_read (which includes lines read by
tcp_expect) is compared against the pattern. If the line
matches, the command given in the key is called with two argu‐
ments: 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 sta‐
tus, the line is not output. Thus a tcp_on_read handler con‐
taining only the instruction `return 1' can be used to suppress
output of particular lines (see, however, tcp_filter above).
However, the line is still stored in TCP_LINE and tcp_lines;
this occurs after all tcp_on_read processing.
TCP UTILITY PARAMETERS
These parameters are controlled by the function system; they may be
read directly, but should not usually be set by user code.
tcp_aliases
Associative array. The keys are the names of sessions estab‐
lished with tcp_open; each value is a space-separated list of
aliases which refer to that session.
tcp_by_fd
Associative array. The keys are session file descriptors; each
value is the name of that session.
tcp_by_name
Associative array. The keys are the names of sessions; each
value is the file descriptor associated with that session.
TCP EXAMPLES
Here is a trivial example using a remote calculator.
To create a calculator server on port 7337 (see the dc manual page for
quite how infuriating the underlying command is):
tcp_proxy 7337 dc
To connect to this from the same host with a session also named `dc':
tcp_open localhost 7337 dc
To send a command to the remote session and wait a short while for out‐
put (assuming dc is the current session):
tcp_command 2 4 + p
To close the session:
tcp_close
The tcp_proxy needs to be killed to be stopped. Note this will not
usually kill any connections which have already been accepted, and also
that the port is not immediately available for reuse.
The following chunk of code puts a list of sessions into an xterm
header, with the current session followed by a star.
print -n "\033]2;TCP:" ${(k)tcp_by_name:/$TCP_SESS/$TCP_SESS\*} "\a"
TCP BUGS
The function tcp_read uses the shell's normal read builtin. As this
reads a complete line at once, data arriving without a terminating new‐
line can cause the function to block indefinitely.
Though the function suite works well for interactive use and for data
arriving in small amounts, the performance when large amounts of data
are being exchanged is likely to be extremely poor.
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