2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2012
4 @c Free Software Foundation, Inc.
5 @c See the file elisp.texi for copying conditions.
6 @node Processes, Display, Abbrevs, Top
13 In the terminology of operating systems, a @dfn{process} is a space in
14 which a program can execute. Emacs runs in a process. Emacs Lisp
15 programs can invoke other programs in processes of their own. These are
16 called @dfn{subprocesses} or @dfn{child processes} of the Emacs process,
17 which is their @dfn{parent process}.
19 A subprocess of Emacs may be @dfn{synchronous} or @dfn{asynchronous},
20 depending on how it is created. When you create a synchronous
21 subprocess, the Lisp program waits for the subprocess to terminate
22 before continuing execution. When you create an asynchronous
23 subprocess, it can run in parallel with the Lisp program. This kind of
24 subprocess is represented within Emacs by a Lisp object which is also
25 called a ``process.'' Lisp programs can use this object to communicate
26 with the subprocess or to control it. For example, you can send
27 signals, obtain status information, receive output from the process, or
30 @defun processp object
31 This function returns @code{t} if @var{object} represents an Emacs
32 subprocess, @code{nil} otherwise.
35 In addition to subprocesses of the current Emacs session, you can
36 also access other processes running on your machine. @xref{System
40 * Subprocess Creation:: Functions that start subprocesses.
41 * Shell Arguments:: Quoting an argument to pass it to a shell.
42 * Synchronous Processes:: Details of using synchronous subprocesses.
43 * Asynchronous Processes:: Starting up an asynchronous subprocess.
44 * Deleting Processes:: Eliminating an asynchronous subprocess.
45 * Process Information:: Accessing run-status and other attributes.
46 * Input to Processes:: Sending input to an asynchronous subprocess.
47 * Signals to Processes:: Stopping, continuing or interrupting
48 an asynchronous subprocess.
49 * Output from Processes:: Collecting output from an asynchronous subprocess.
50 * Sentinels:: Sentinels run when process run-status changes.
51 * Query Before Exit:: Whether to query if exiting will kill a process.
52 * System Processes:: Accessing other processes running on your system.
53 * Transaction Queues:: Transaction-based communication with subprocesses.
54 * Network:: Opening network connections.
55 * Network Servers:: Network servers let Emacs accept net connections.
56 * Datagrams:: UDP network connections.
57 * Low-Level Network:: Lower-level but more general function
58 to create connections and servers.
59 * Misc Network:: Additional relevant functions for net connections.
60 * Serial Ports:: Communicating with serial ports.
61 * Byte Packing:: Using bindat to pack and unpack binary data.
64 @node Subprocess Creation
65 @section Functions that Create Subprocesses
67 There are three primitives that create a new subprocess in which to run
68 a program. One of them, @code{start-process}, creates an asynchronous
69 process and returns a process object (@pxref{Asynchronous Processes}).
70 The other two, @code{call-process} and @code{call-process-region},
71 create a synchronous process and do not return a process object
72 (@pxref{Synchronous Processes}).
74 Synchronous and asynchronous processes are explained in the following
75 sections. Since the three functions are all called in a similar
76 fashion, their common arguments are described here.
78 @cindex execute program
79 @cindex @env{PATH} environment variable
80 @cindex @env{HOME} environment variable
81 In all cases, the function's @var{program} argument specifies the
82 program to be run. An error is signaled if the file is not found or
83 cannot be executed. If the file name is relative, the variable
84 @code{exec-path} contains a list of directories to search. Emacs
85 initializes @code{exec-path} when it starts up, based on the value of
86 the environment variable @env{PATH}. The standard file name
87 constructs, @samp{~}, @samp{.}, and @samp{..}, are interpreted as
88 usual in @code{exec-path}, but environment variable substitutions
89 (@samp{$HOME}, etc.) are not recognized; use
90 @code{substitute-in-file-name} to perform them (@pxref{File Name
91 Expansion}). @code{nil} in this list refers to
92 @code{default-directory}.
94 Executing a program can also try adding suffixes to the specified
98 This variable is a list of suffixes (strings) to try adding to the
99 specified program file name. The list should include @code{""} if you
100 want the name to be tried exactly as specified. The default value is
104 @strong{Please note:} The argument @var{program} contains only the
105 name of the program; it may not contain any command-line arguments. You
106 must use @var{args} to provide those.
108 Each of the subprocess-creating functions has a @var{buffer-or-name}
109 argument which specifies where the standard output from the program will
110 go. It should be a buffer or a buffer name; if it is a buffer name,
111 that will create the buffer if it does not already exist. It can also
112 be @code{nil}, which says to discard the output unless a filter function
113 handles it. (@xref{Filter Functions}, and @ref{Read and Print}.)
114 Normally, you should avoid having multiple processes send output to the
115 same buffer because their output would be intermixed randomly.
117 @cindex program arguments
118 All three of the subprocess-creating functions have a @code{&rest}
119 argument, @var{args}. The @var{args} must all be strings, and they are
120 supplied to @var{program} as separate command line arguments. Wildcard
121 characters and other shell constructs have no special meanings in these
122 strings, since the strings are passed directly to the specified program.
124 The subprocess gets its current directory from the value of
125 @code{default-directory} (@pxref{File Name Expansion}).
127 @cindex environment variables, subprocesses
128 The subprocess inherits its environment from Emacs, but you can
129 specify overrides for it with @code{process-environment}. @xref{System
132 @defvar exec-directory
134 The value of this variable is a string, the name of a directory that
135 contains programs that come with GNU Emacs, programs intended for Emacs
136 to invoke. The program @code{movemail} is an example of such a program;
137 Rmail uses it to fetch new mail from an inbox.
141 The value of this variable is a list of directories to search for
142 programs to run in subprocesses. Each element is either the name of a
143 directory (i.e., a string), or @code{nil}, which stands for the default
144 directory (which is the value of @code{default-directory}).
145 @cindex program directories
147 The value of @code{exec-path} is used by @code{call-process} and
148 @code{start-process} when the @var{program} argument is not an absolute
152 @node Shell Arguments
153 @section Shell Arguments
154 @cindex arguments for shell commands
155 @cindex shell command arguments
157 Lisp programs sometimes need to run a shell and give it a command
158 that contains file names that were specified by the user. These
159 programs ought to be able to support any valid file name. But the shell
160 gives special treatment to certain characters, and if these characters
161 occur in the file name, they will confuse the shell. To handle these
162 characters, use the function @code{shell-quote-argument}:
164 @defun shell-quote-argument argument
165 This function returns a string which represents, in shell syntax,
166 an argument whose actual contents are @var{argument}. It should
167 work reliably to concatenate the return value into a shell command
168 and then pass it to a shell for execution.
170 Precisely what this function does depends on your operating system. The
171 function is designed to work with the syntax of your system's standard
172 shell; if you use an unusual shell, you will need to redefine this
176 ;; @r{This example shows the behavior on GNU and Unix systems.}
177 (shell-quote-argument "foo > bar")
178 @result{} "foo\\ \\>\\ bar"
180 ;; @r{This example shows the behavior on MS-DOS and MS-Windows.}
181 (shell-quote-argument "foo > bar")
182 @result{} "\"foo > bar\""
185 Here's an example of using @code{shell-quote-argument} to construct
190 (shell-quote-argument oldfile)
192 (shell-quote-argument newfile))
196 @cindex quoting and unquoting command-line arguments
197 @cindex minibuffer input, and command-line arguments
198 @cindex @code{call-process}, command-line arguments from minibuffer
199 @cindex @code{start-process}, command-line arguments from minibuffer
200 The following two functions are useful for combining a list of
201 individual command-line argument strings into a single string, and
202 taking a string apart into a list of individual command-line
203 arguments. These functions are mainly intended to be used for
204 converting user input in the minibuffer, a Lisp string, into a list of
205 string arguments to be passed to @code{call-process} or
206 @code{start-process}, or for the converting such lists of arguments in
207 a single Lisp string to be presented in the minibuffer or echo area.
209 @defun split-string-and-unquote string &optional separators
210 This function splits @var{string} into substrings at matches for the
211 regular expression @var{separators}, like @code{split-string} does
212 (@pxref{Creating Strings}); in addition, it removes quoting from the
213 substrings. It then makes a list of the substrings and returns it.
215 If @var{separators} is omitted or @code{nil}, it defaults to
216 @code{"\\s-+"}, which is a regular expression that matches one or more
217 characters with whitespace syntax (@pxref{Syntax Class Table}).
219 This function supports two types of quoting: enclosing a whole string
220 in double quotes @code{"@dots{}"}, and quoting individual characters
221 with a backslash escape @samp{\}. The latter is also used in Lisp
222 strings, so this function can handle those as well.
225 @defun combine-and-quote-strings list-of-strings &optional separator
226 This function concatenates @var{list-of-strings} into a single string,
227 quoting each string as necessary. It also sticks the @var{separator}
228 string between each pair of strings; if @var{separator} is omitted or
229 @code{nil}, it defaults to @code{" "}. The return value is the
232 The strings in @var{list-of-strings} that need quoting are those that
233 include @var{separator} as their substring. Quoting a string encloses
234 it in double quotes @code{"@dots{}"}. In the simplest case, if you
235 are consing a command from the individual command-line arguments,
236 every argument that includes embedded blanks will be quoted.
239 @node Synchronous Processes
240 @section Creating a Synchronous Process
241 @cindex synchronous subprocess
243 After a @dfn{synchronous process} is created, Emacs waits for the
244 process to terminate before continuing. Starting Dired on GNU or
245 Unix@footnote{On other systems, Emacs uses a Lisp emulation of
246 @code{ls}; see @ref{Contents of Directories}.} is an example of this: it
247 runs @code{ls} in a synchronous process, then modifies the output
248 slightly. Because the process is synchronous, the entire directory
249 listing arrives in the buffer before Emacs tries to do anything with it.
251 While Emacs waits for the synchronous subprocess to terminate, the
252 user can quit by typing @kbd{C-g}. The first @kbd{C-g} tries to kill
253 the subprocess with a @code{SIGINT} signal; but it waits until the
254 subprocess actually terminates before quitting. If during that time the
255 user types another @kbd{C-g}, that kills the subprocess instantly with
256 @code{SIGKILL} and quits immediately (except on MS-DOS, where killing
257 other processes doesn't work). @xref{Quitting}.
259 The synchronous subprocess functions return an indication of how the
262 The output from a synchronous subprocess is generally decoded using a
263 coding system, much like text read from a file. The input sent to a
264 subprocess by @code{call-process-region} is encoded using a coding
265 system, much like text written into a file. @xref{Coding Systems}.
267 @defun call-process program &optional infile destination display &rest args
268 This function calls @var{program} and waits for it to finish.
270 The current working directory of the subprocess is
271 @code{default-directory}.
273 The standard input for the new process comes from file @var{infile} if
274 @var{infile} is not @code{nil}, and from the null device otherwise.
275 The argument @var{destination} says where to put the process output.
276 Here are the possibilities:
280 Insert the output in that buffer, before point. This includes both the
281 standard output stream and the standard error stream of the process.
284 Insert the output in a buffer with that name, before point.
287 Insert the output in the current buffer, before point.
293 Discard the output, and return @code{nil} immediately without waiting
294 for the subprocess to finish.
296 In this case, the process is not truly synchronous, since it can run in
297 parallel with Emacs; but you can think of it as synchronous in that
298 Emacs is essentially finished with the subprocess as soon as this
301 MS-DOS doesn't support asynchronous subprocesses, so this option doesn't
304 @item @code{(:file @var{file-name})}
305 Send the output to the file name specified, overwriting it if it
308 @item @code{(@var{real-destination} @var{error-destination})}
309 Keep the standard output stream separate from the standard error stream;
310 deal with the ordinary output as specified by @var{real-destination},
311 and dispose of the error output according to @var{error-destination}.
312 If @var{error-destination} is @code{nil}, that means to discard the
313 error output, @code{t} means mix it with the ordinary output, and a
314 string specifies a file name to redirect error output into.
316 You can't directly specify a buffer to put the error output in; that is
317 too difficult to implement. But you can achieve this result by sending
318 the error output to a temporary file and then inserting the file into a
322 If @var{display} is non-@code{nil}, then @code{call-process} redisplays
323 the buffer as output is inserted. (However, if the coding system chosen
324 for decoding output is @code{undecided}, meaning deduce the encoding
325 from the actual data, then redisplay sometimes cannot continue once
326 non-@acronym{ASCII} characters are encountered. There are fundamental
327 reasons why it is hard to fix this; see @ref{Output from Processes}.)
329 Otherwise the function @code{call-process} does no redisplay, and the
330 results become visible on the screen only when Emacs redisplays that
331 buffer in the normal course of events.
333 The remaining arguments, @var{args}, are strings that specify command
334 line arguments for the program.
336 The value returned by @code{call-process} (unless you told it not to
337 wait) indicates the reason for process termination. A number gives the
338 exit status of the subprocess; 0 means success, and any other value
339 means failure. If the process terminated with a signal,
340 @code{call-process} returns a string describing the signal.
342 In the examples below, the buffer @samp{foo} is current.
346 (call-process "pwd" nil t)
349 ---------- Buffer: foo ----------
350 /usr/user/lewis/manual
351 ---------- Buffer: foo ----------
355 (call-process "grep" nil "bar" nil "lewis" "/etc/passwd")
358 ---------- Buffer: bar ----------
359 lewis:5LTsHm66CSWKg:398:21:Bil Lewis:/user/lewis:/bin/csh
361 ---------- Buffer: bar ----------
365 Here is a good example of the use of @code{call-process}, which used to
366 be found in the definition of @code{insert-directory}:
370 (call-process insert-directory-program nil t nil @var{switches}
372 (concat (file-name-as-directory file) ".")
378 @defun process-file program &optional infile buffer display &rest args
379 This function processes files synchronously in a separate process. It
380 is similar to @code{call-process} but may invoke a file handler based
381 on the value of the variable @code{default-directory}. The current
382 working directory of the subprocess is @code{default-directory}.
384 The arguments are handled in almost the same way as for
385 @code{call-process}, with the following differences:
387 Some file handlers may not support all combinations and forms of the
388 arguments @var{infile}, @var{buffer}, and @var{display}. For example,
389 some file handlers might behave as if @var{display} were @code{nil},
390 regardless of the value actually passed. As another example, some
391 file handlers might not support separating standard output and error
392 output by way of the @var{buffer} argument.
394 If a file handler is invoked, it determines the program to run based
395 on the first argument @var{program}. For instance, consider that a
396 handler for remote files is invoked. Then the path that is used for
397 searching the program might be different than @code{exec-path}.
399 The second argument @var{infile} may invoke a file handler. The file
400 handler could be different from the handler chosen for the
401 @code{process-file} function itself. (For example,
402 @code{default-directory} could be on a remote host, whereas
403 @var{infile} is on another remote host. Or @code{default-directory}
404 could be non-special, whereas @var{infile} is on a remote host.)
406 If @var{buffer} is a list of the form @code{(@var{real-destination}
407 @var{error-destination})}, and @var{error-destination} names a file,
408 then the same remarks as for @var{infile} apply.
410 The remaining arguments (@var{args}) will be passed to the process
411 verbatim. Emacs is not involved in processing file names that are
412 present in @var{args}. To avoid confusion, it may be best to avoid
413 absolute file names in @var{args}, but rather to specify all file
414 names as relative to @code{default-directory}. The function
415 @code{file-relative-name} is useful for constructing such relative
419 @defvar process-file-side-effects
420 This variable indicates, whether a call of @code{process-file} changes
423 Per default, this variable is always set to @code{t}, meaning that a
424 call of @code{process-file} could potentially change any file on a
425 remote host. When set to @code{nil}, a file handler could optimize
426 its behavior with respect to remote file attributes caching.
428 This variable should never be changed by @code{setq}. Instead of, it
429 shall be set only by let-binding.
432 @defun call-process-region start end program &optional delete destination display &rest args
433 This function sends the text from @var{start} to @var{end} as
434 standard input to a process running @var{program}. It deletes the text
435 sent if @var{delete} is non-@code{nil}; this is useful when
436 @var{destination} is @code{t}, to insert the output in the current
437 buffer in place of the input.
439 The arguments @var{destination} and @var{display} control what to do
440 with the output from the subprocess, and whether to update the display
441 as it comes in. For details, see the description of
442 @code{call-process}, above. If @var{destination} is the integer 0,
443 @code{call-process-region} discards the output and returns @code{nil}
444 immediately, without waiting for the subprocess to finish (this only
445 works if asynchronous subprocesses are supported).
447 The remaining arguments, @var{args}, are strings that specify command
448 line arguments for the program.
450 The return value of @code{call-process-region} is just like that of
451 @code{call-process}: @code{nil} if you told it to return without
452 waiting; otherwise, a number or string which indicates how the
453 subprocess terminated.
455 In the following example, we use @code{call-process-region} to run the
456 @code{cat} utility, with standard input being the first five characters
457 in buffer @samp{foo} (the word @samp{input}). @code{cat} copies its
458 standard input into its standard output. Since the argument
459 @var{destination} is @code{t}, this output is inserted in the current
464 ---------- Buffer: foo ----------
466 ---------- Buffer: foo ----------
470 (call-process-region 1 6 "cat" nil t)
473 ---------- Buffer: foo ----------
475 ---------- Buffer: foo ----------
479 The @code{shell-command-on-region} command uses
480 @code{call-process-region} like this:
486 shell-file-name ; @r{Name of program.}
487 nil ; @r{Do not delete region.}
488 buffer ; @r{Send output to @code{buffer}.}
489 nil ; @r{No redisplay during output.}
490 "-c" command) ; @r{Arguments for the shell.}
495 @defun call-process-shell-command command &optional infile destination display &rest args
496 This function executes the shell command @var{command} synchronously.
497 The final arguments @var{args} are additional arguments to add at the
498 end of @var{command}. The other arguments are handled as in
502 @defun process-file-shell-command command &optional infile destination display &rest args
503 This function is like @code{call-process-shell-command}, but uses
504 @code{process-file} internally. Depending on @code{default-directory},
505 @var{command} can be executed also on remote hosts.
508 @defun shell-command-to-string command
509 This function executes @var{command} (a string) as a shell command,
510 then returns the command's output as a string.
513 @defun process-lines program &rest args
514 This function runs @var{program}, waits for it to finish, and returns
515 its output as a list of strings. Each string in the list holds a
516 single line of text output by the program; the end-of-line characters
517 are stripped from each line. The arguments beyond @var{program},
518 @var{args}, are strings that specify command-line arguments with which
521 If @var{program} exits with a non-zero exit status, this function
524 This function works by calling @code{call-process}, so program output
525 is decoded in the same way as for @code{call-process}.
528 @node Asynchronous Processes
529 @section Creating an Asynchronous Process
530 @cindex asynchronous subprocess
532 After an @dfn{asynchronous process} is created, Emacs and the subprocess
533 both continue running immediately. The process thereafter runs
534 in parallel with Emacs, and the two can communicate with each other
535 using the functions described in the following sections. However,
536 communication is only partially asynchronous: Emacs sends data to the
537 process only when certain functions are called, and Emacs accepts data
538 from the process only when Emacs is waiting for input or for a time
541 Here we describe how to create an asynchronous process.
543 @defun start-process name buffer-or-name program &rest args
544 This function creates a new asynchronous subprocess and starts the
545 program @var{program} running in it. It returns a process object that
546 stands for the new subprocess in Lisp. The argument @var{name}
547 specifies the name for the process object; if a process with this name
548 already exists, then @var{name} is modified (by appending @samp{<1>},
549 etc.) to be unique. The buffer @var{buffer-or-name} is the buffer to
550 associate with the process.
552 The remaining arguments, @var{args}, are strings that specify command
553 line arguments for the program.
555 In the example below, the first process is started and runs (rather,
556 sleeps) for 100 seconds. Meanwhile, the second process is started, and
557 given the name @samp{my-process<1>} for the sake of uniqueness. It
558 inserts the directory listing at the end of the buffer @samp{foo},
559 before the first process finishes. Then it finishes, and a message to
560 that effect is inserted in the buffer. Much later, the first process
561 finishes, and another message is inserted in the buffer for it.
565 (start-process "my-process" "foo" "sleep" "100")
566 @result{} #<process my-process>
570 (start-process "my-process" "foo" "ls" "-l" "/user/lewis/bin")
571 @result{} #<process my-process<1>>
573 ---------- Buffer: foo ----------
575 lrwxrwxrwx 1 lewis 14 Jul 22 10:12 gnuemacs --> /emacs
576 -rwxrwxrwx 1 lewis 19 Jul 30 21:02 lemon
578 Process my-process<1> finished
580 Process my-process finished
581 ---------- Buffer: foo ----------
586 @defun start-file-process name buffer-or-name program &rest args
587 Like @code{start-process}, this function starts a new asynchronous
588 subprocess running @var{program} in it, and returns its process
589 object---when @code{default-directory} is not a magic file name.
591 If @code{default-directory} is magic, the function invokes its file
592 handler instead. This handler ought to run @var{program}, perhaps on
593 the local host, perhaps on a remote host that corresponds to
594 @code{default-directory}. In the latter case, the local part of
595 @code{default-directory} becomes the working directory of the process.
597 This function does not try to invoke file name handlers for
598 @var{program} or for the @var{program-args}.
600 Depending on the implementation of the file handler, it might not be
601 possible to apply @code{process-filter} or @code{process-sentinel} to
602 the resulting process object (@pxref{Filter Functions}, @pxref{Sentinels}).
604 Some file handlers may not support @code{start-file-process} (for
605 example @code{ange-ftp-hook-function}). In such cases, the function
606 does nothing and returns @code{nil}.
609 @defun start-process-shell-command name buffer-or-name command
610 This function is like @code{start-process} except that it uses a shell
611 to execute the specified command. The argument @var{command} is a shell
612 command name. The variable @code{shell-file-name} specifies which shell to
615 The point of running a program through the shell, rather than directly
616 with @code{start-process}, is so that you can employ shell features such
617 as wildcards in the arguments. It follows that if you include an
618 arbitrary user-specified arguments in the command, you should quote it
619 with @code{shell-quote-argument} first, so that any special shell
620 characters do @emph{not} have their special shell meanings. @xref{Shell
624 @defun start-file-process-shell-command name buffer-or-name command
625 This function is like @code{start-process-shell-command}, but uses
626 @code{start-file-process} internally. By this, @var{command} can be
627 executed also on remote hosts, depending on @code{default-directory}.
630 @defvar process-connection-type
632 @cindex @acronym{PTY}s
633 This variable controls the type of device used to communicate with
634 asynchronous subprocesses. If it is non-@code{nil}, then @acronym{PTY}s are
635 used, when available. Otherwise, pipes are used.
637 @acronym{PTY}s are usually preferable for processes visible to the user, as
638 in Shell mode, because they allow job control (@kbd{C-c}, @kbd{C-z},
639 etc.) to work between the process and its children, whereas pipes do
640 not. For subprocesses used for internal purposes by programs, it is
641 often better to use a pipe, because they are more efficient. In
642 addition, the total number of @acronym{PTY}s is limited on many systems and
643 it is good not to waste them.
645 The value of @code{process-connection-type} takes effect when
646 @code{start-process} is called. So you can specify how to communicate
647 with one subprocess by binding the variable around the call to
648 @code{start-process}.
652 (let ((process-connection-type nil)) ; @r{Use a pipe.}
653 (start-process @dots{}))
657 To determine whether a given subprocess actually got a pipe or a
658 @acronym{PTY}, use the function @code{process-tty-name} (@pxref{Process
662 @node Deleting Processes
663 @section Deleting Processes
664 @cindex deleting processes
666 @dfn{Deleting a process} disconnects Emacs immediately from the
667 subprocess. Processes are deleted automatically after they terminate,
668 but not necessarily right away. You can delete a process explicitly
669 at any time. If you delete a terminated process explicitly before it
670 is deleted automatically, no harm results. Deleting a running
671 process sends a signal to terminate it (and its child processes if
672 any), and calls the process sentinel if it has one. @xref{Sentinels}.
674 When a process is deleted, the process object itself continues to
675 exist as long as other Lisp objects point to it. All the Lisp
676 primitives that work on process objects accept deleted processes, but
677 those that do I/O or send signals will report an error. The process
678 mark continues to point to the same place as before, usually into a
679 buffer where output from the process was being inserted.
681 @defopt delete-exited-processes
682 This variable controls automatic deletion of processes that have
683 terminated (due to calling @code{exit} or to a signal). If it is
684 @code{nil}, then they continue to exist until the user runs
685 @code{list-processes}. Otherwise, they are deleted immediately after
689 @defun delete-process process
690 This function deletes a process, killing it with a @code{SIGKILL}
691 signal. The argument may be a process, the name of a process, a
692 buffer, or the name of a buffer. (A buffer or buffer-name stands for
693 the process that @code{get-buffer-process} returns.) Calling
694 @code{delete-process} on a running process terminates it, updates the
695 process status, and runs the sentinel (if any) immediately. If the
696 process has already terminated, calling @code{delete-process} has no
697 effect on its status, or on the running of its sentinel (which will
698 happen sooner or later).
702 (delete-process "*shell*")
708 @node Process Information
709 @section Process Information
711 Several functions return information about processes.
712 @code{list-processes} is provided for interactive use.
714 @deffn Command list-processes &optional query-only
715 This command displays a listing of all living processes. In addition,
716 it finally deletes any process whose status was @samp{Exited} or
717 @samp{Signaled}. It returns @code{nil}.
719 The processes are shown in a buffer named @file{*Process List*}, whose
720 major mode is named Process Menu mode.
722 If @var{query-only} is non-@code{nil} then it lists only processes
723 whose query flag is non-@code{nil}. @xref{Query Before Exit}.
727 This function returns a list of all processes that have not been deleted.
732 @result{} (#<process display-time> #<process shell>)
737 @defun get-process name
738 This function returns the process named @var{name}, or @code{nil} if
739 there is none. An error is signaled if @var{name} is not a string.
743 (get-process "shell")
744 @result{} #<process shell>
749 @defun process-command process
750 This function returns the command that was executed to start
751 @var{process}. This is a list of strings, the first string being the
752 program executed and the rest of the strings being the arguments that
753 were given to the program.
757 (process-command (get-process "shell"))
758 @result{} ("/bin/csh" "-i")
763 @defun process-contact process &optional key
765 This function returns information about how a network or serial
766 process was set up. For a network process, when @var{key} is
767 @code{nil}, it returns @code{(@var{hostname} @var{service})} which
768 specifies what you connected to. For a serial process, when @var{key}
769 is @code{nil}, it returns @code{(@var{port} @var{speed})}. For an
770 ordinary child process, this function always returns @code{t}.
772 If @var{key} is @code{t}, the value is the complete status information
773 for the connection, server, or serial port; that is, the list of
774 keywords and values specified in @code{make-network-process} or
775 @code{make-serial-process}, except that some of the values represent
776 the current status instead of what you specified.
778 For a network process:
782 The associated value is the process buffer.
784 The associated value is the process filter function.
786 The associated value is the process sentinel function.
788 In a connection, the address in internal format of the remote peer.
790 The local address, in internal format.
792 In a server, if you specified @code{t} for @var{service},
793 this value is the actual port number.
796 @code{:local} and @code{:remote} are included even if they were not
797 specified explicitly in @code{make-network-process}.
799 For a serial process, see @code{make-serial-process} and
800 @code{serial-process-configure} for a list of keys.
802 If @var{key} is a keyword, the function returns the value corresponding
806 @defun process-id process
807 This function returns the @acronym{PID} of @var{process}. This is an
808 integer that distinguishes the process @var{process} from all other
809 processes running on the same computer at the current time. The
810 @acronym{PID} of a process is chosen by the operating system kernel when the
811 process is started and remains constant as long as the process exists.
814 @defun process-name process
815 This function returns the name of @var{process}.
818 @defun process-status process-name
819 This function returns the status of @var{process-name} as a symbol.
820 The argument @var{process-name} must be a process, a buffer, or a
821 process name (a string).
823 The possible values for an actual subprocess are:
827 for a process that is running.
829 for a process that is stopped but continuable.
831 for a process that has exited.
833 for a process that has received a fatal signal.
835 for a network connection that is open.
837 for a network connection that is closed. Once a connection
838 is closed, you cannot reopen it, though you might be able to open
839 a new connection to the same place.
841 for a non-blocking connection that is waiting to complete.
843 for a non-blocking connection that has failed to complete.
845 for a network server that is listening.
847 if @var{process-name} is not the name of an existing process.
852 (process-status (get-buffer "*shell*"))
857 @result{} #<process xx<1>>
863 For a network connection, @code{process-status} returns one of the symbols
864 @code{open} or @code{closed}. The latter means that the other side
865 closed the connection, or Emacs did @code{delete-process}.
868 @defun process-live-p process
869 This function returns nin-@code{nil} if @var{process} is alive. A
870 process is considered alive if its status is @code{run}, @code{open},
871 @code{listen}, @code{connect} or @code{stop}.
874 @defun process-type process
875 This function returns the symbol @code{network} for a network
876 connection or server, @code{serial} for a serial port connection, or
877 @code{real} for a real subprocess.
880 @defun process-exit-status process
881 This function returns the exit status of @var{process} or the signal
882 number that killed it. (Use the result of @code{process-status} to
883 determine which of those it is.) If @var{process} has not yet
884 terminated, the value is 0.
887 @defun process-tty-name process
888 This function returns the terminal name that @var{process} is using for
889 its communication with Emacs---or @code{nil} if it is using pipes
890 instead of a terminal (see @code{process-connection-type} in
891 @ref{Asynchronous Processes}). If @var{process} represents a program
892 running on a remote host, the terminal name used by that program on
893 the remote host is provided as process property @code{remote-tty}.
896 @defun process-coding-system process
897 @anchor{Coding systems for a subprocess}
898 This function returns a cons cell describing the coding systems in use
899 for decoding output from @var{process} and for encoding input to
900 @var{process} (@pxref{Coding Systems}). The value has this form:
903 (@var{coding-system-for-decoding} . @var{coding-system-for-encoding})
907 @defun set-process-coding-system process &optional decoding-system encoding-system
908 This function specifies the coding systems to use for subsequent output
909 from and input to @var{process}. It will use @var{decoding-system} to
910 decode subprocess output, and @var{encoding-system} to encode subprocess
914 Every process also has a property list that you can use to store
915 miscellaneous values associated with the process.
917 @defun process-get process propname
918 This function returns the value of the @var{propname} property
922 @defun process-put process propname value
923 This function sets the value of the @var{propname} property
924 of @var{process} to @var{value}.
927 @defun process-plist process
928 This function returns the process plist of @var{process}.
931 @defun set-process-plist process plist
932 This function sets the process plist of @var{process} to @var{plist}.
935 @node Input to Processes
936 @section Sending Input to Processes
937 @cindex process input
939 Asynchronous subprocesses receive input when it is sent to them by
940 Emacs, which is done with the functions in this section. You must
941 specify the process to send input to, and the input data to send. The
942 data appears on the ``standard input'' of the subprocess.
944 Some operating systems have limited space for buffered input in a
945 @acronym{PTY}. On these systems, Emacs sends an @acronym{EOF}
946 periodically amidst the other characters, to force them through. For
947 most programs, these @acronym{EOF}s do no harm.
949 Subprocess input is normally encoded using a coding system before the
950 subprocess receives it, much like text written into a file. You can use
951 @code{set-process-coding-system} to specify which coding system to use
952 (@pxref{Process Information}). Otherwise, the coding system comes from
953 @code{coding-system-for-write}, if that is non-@code{nil}; or else from
954 the defaulting mechanism (@pxref{Default Coding Systems}).
956 Sometimes the system is unable to accept input for that process,
957 because the input buffer is full. When this happens, the send functions
958 wait a short while, accepting output from subprocesses, and then try
959 again. This gives the subprocess a chance to read more of its pending
960 input and make space in the buffer. It also allows filters, sentinels
961 and timers to run---so take account of that in writing your code.
963 In these functions, the @var{process} argument can be a process or
964 the name of a process, or a buffer or buffer name (which stands
965 for a process via @code{get-buffer-process}). @code{nil} means
966 the current buffer's process.
968 @defun process-send-string process string
969 This function sends @var{process} the contents of @var{string} as
970 standard input. If it is @code{nil}, the current buffer's process is used.
972 The function returns @code{nil}.
976 (process-send-string "shell<1>" "ls\n")
982 ---------- Buffer: *shell* ----------
984 introduction.texi syntax-tables.texi~
985 introduction.texi~ text.texi
986 introduction.txt text.texi~
988 ---------- Buffer: *shell* ----------
993 @defun process-send-region process start end
994 This function sends the text in the region defined by @var{start} and
995 @var{end} as standard input to @var{process}.
997 An error is signaled unless both @var{start} and @var{end} are
998 integers or markers that indicate positions in the current buffer. (It
999 is unimportant which number is larger.)
1002 @defun process-send-eof &optional process
1003 This function makes @var{process} see an end-of-file in its
1004 input. The @acronym{EOF} comes after any text already sent to it.
1006 The function returns @var{process}.
1010 (process-send-eof "shell")
1016 @defun process-running-child-p &optional process
1017 This function will tell you whether a @var{process} has given control of
1018 its terminal to its own child process. The value is @code{t} if this is
1019 true, or if Emacs cannot tell; it is @code{nil} if Emacs can be certain
1020 that this is not so.
1023 @node Signals to Processes
1024 @section Sending Signals to Processes
1025 @cindex process signals
1026 @cindex sending signals
1029 @dfn{Sending a signal} to a subprocess is a way of interrupting its
1030 activities. There are several different signals, each with its own
1031 meaning. The set of signals and their names is defined by the operating
1032 system. For example, the signal @code{SIGINT} means that the user has
1033 typed @kbd{C-c}, or that some analogous thing has happened.
1035 Each signal has a standard effect on the subprocess. Most signals
1036 kill the subprocess, but some stop or resume execution instead. Most
1037 signals can optionally be handled by programs; if the program handles
1038 the signal, then we can say nothing in general about its effects.
1040 You can send signals explicitly by calling the functions in this
1041 section. Emacs also sends signals automatically at certain times:
1042 killing a buffer sends a @code{SIGHUP} signal to all its associated
1043 processes; killing Emacs sends a @code{SIGHUP} signal to all remaining
1044 processes. (@code{SIGHUP} is a signal that usually indicates that the
1045 user hung up the phone.)
1047 Each of the signal-sending functions takes two optional arguments:
1048 @var{process} and @var{current-group}.
1050 The argument @var{process} must be either a process, a process
1051 name, a buffer, a buffer name, or @code{nil}. A buffer or buffer name
1052 stands for a process through @code{get-buffer-process}. @code{nil}
1053 stands for the process associated with the current buffer. An error
1054 is signaled if @var{process} does not identify a process.
1056 The argument @var{current-group} is a flag that makes a difference
1057 when you are running a job-control shell as an Emacs subprocess. If it
1058 is non-@code{nil}, then the signal is sent to the current process-group
1059 of the terminal that Emacs uses to communicate with the subprocess. If
1060 the process is a job-control shell, this means the shell's current
1061 subjob. If it is @code{nil}, the signal is sent to the process group of
1062 the immediate subprocess of Emacs. If the subprocess is a job-control
1063 shell, this is the shell itself.
1065 The flag @var{current-group} has no effect when a pipe is used to
1066 communicate with the subprocess, because the operating system does not
1067 support the distinction in the case of pipes. For the same reason,
1068 job-control shells won't work when a pipe is used. See
1069 @code{process-connection-type} in @ref{Asynchronous Processes}.
1071 @defun interrupt-process &optional process current-group
1072 This function interrupts the process @var{process} by sending the
1073 signal @code{SIGINT}. Outside of Emacs, typing the ``interrupt
1074 character'' (normally @kbd{C-c} on some systems, and @code{DEL} on
1075 others) sends this signal. When the argument @var{current-group} is
1076 non-@code{nil}, you can think of this function as ``typing @kbd{C-c}''
1077 on the terminal by which Emacs talks to the subprocess.
1080 @defun kill-process &optional process current-group
1081 This function kills the process @var{process} by sending the
1082 signal @code{SIGKILL}. This signal kills the subprocess immediately,
1083 and cannot be handled by the subprocess.
1086 @defun quit-process &optional process current-group
1087 This function sends the signal @code{SIGQUIT} to the process
1088 @var{process}. This signal is the one sent by the ``quit
1089 character'' (usually @kbd{C-b} or @kbd{C-\}) when you are not inside
1093 @defun stop-process &optional process current-group
1094 This function stops the process @var{process} by sending the
1095 signal @code{SIGTSTP}. Use @code{continue-process} to resume its
1098 Outside of Emacs, on systems with job control, the ``stop character''
1099 (usually @kbd{C-z}) normally sends this signal. When
1100 @var{current-group} is non-@code{nil}, you can think of this function as
1101 ``typing @kbd{C-z}'' on the terminal Emacs uses to communicate with the
1105 @defun continue-process &optional process current-group
1106 This function resumes execution of the process @var{process} by sending
1107 it the signal @code{SIGCONT}. This presumes that @var{process} was
1111 @defun signal-process process signal
1112 This function sends a signal to process @var{process}. The argument
1113 @var{signal} specifies which signal to send; it should be an integer.
1115 The @var{process} argument can be a system process @acronym{ID}; that
1116 allows you to send signals to processes that are not children of
1117 Emacs. @xref{System Processes}.
1120 @node Output from Processes
1121 @section Receiving Output from Processes
1122 @cindex process output
1123 @cindex output from processes
1125 There are two ways to receive the output that a subprocess writes to
1126 its standard output stream. The output can be inserted in a buffer,
1127 which is called the associated buffer of the process, or a function
1128 called the @dfn{filter function} can be called to act on the output. If
1129 the process has no buffer and no filter function, its output is
1132 When a subprocess terminates, Emacs reads any pending output,
1133 then stops reading output from that subprocess. Therefore, if the
1134 subprocess has children that are still live and still producing
1135 output, Emacs won't receive that output.
1137 Output from a subprocess can arrive only while Emacs is waiting: when
1138 reading terminal input, in @code{sit-for} and @code{sleep-for}
1139 (@pxref{Waiting}), and in @code{accept-process-output} (@pxref{Accepting
1140 Output}). This minimizes the problem of timing errors that usually
1141 plague parallel programming. For example, you can safely create a
1142 process and only then specify its buffer or filter function; no output
1143 can arrive before you finish, if the code in between does not call any
1144 primitive that waits.
1146 @defvar process-adaptive-read-buffering
1147 On some systems, when Emacs reads the output from a subprocess, the
1148 output data is read in very small blocks, potentially resulting in
1149 very poor performance. This behavior can be remedied to some extent
1150 by setting the variable @var{process-adaptive-read-buffering} to a
1151 non-@code{nil} value (the default), as it will automatically delay reading
1152 from such processes, thus allowing them to produce more output before
1153 Emacs tries to read it.
1156 It is impossible to separate the standard output and standard error
1157 streams of the subprocess, because Emacs normally spawns the subprocess
1158 inside a pseudo-TTY, and a pseudo-TTY has only one output channel. If
1159 you want to keep the output to those streams separate, you should
1160 redirect one of them to a file---for example, by using an appropriate
1164 * Process Buffers:: If no filter, output is put in a buffer.
1165 * Filter Functions:: Filter functions accept output from the process.
1166 * Decoding Output:: Filters can get unibyte or multibyte strings.
1167 * Accepting Output:: How to wait until process output arrives.
1170 @node Process Buffers
1171 @subsection Process Buffers
1173 A process can (and usually does) have an @dfn{associated buffer},
1174 which is an ordinary Emacs buffer that is used for two purposes: storing
1175 the output from the process, and deciding when to kill the process. You
1176 can also use the buffer to identify a process to operate on, since in
1177 normal practice only one process is associated with any given buffer.
1178 Many applications of processes also use the buffer for editing input to
1179 be sent to the process, but this is not built into Emacs Lisp.
1181 Unless the process has a filter function (@pxref{Filter Functions}),
1182 its output is inserted in the associated buffer. The position to insert
1183 the output is determined by the @code{process-mark}, which is then
1184 updated to point to the end of the text just inserted. Usually, but not
1185 always, the @code{process-mark} is at the end of the buffer.
1187 @findex process-kill-buffer-query-function
1188 Killing the associated buffer of a process also kills the process.
1189 Emacs asks for confirmation first, if the process's
1190 @code{process-query-on-exit-flag} is non-@code{nil} (@pxref{Query
1191 Before Exit}). This confirmation is done by the function
1192 @code{process-kill-buffer-query-function}, which is run from
1193 @code{kill-buffer-query-functions} (@pxref{Killing Buffers}).
1195 @defun process-buffer process
1196 This function returns the associated buffer of the process
1201 (process-buffer (get-process "shell"))
1202 @result{} #<buffer *shell*>
1207 @defun process-mark process
1208 This function returns the process marker for @var{process}, which is the
1209 marker that says where to insert output from the process.
1211 If @var{process} does not have a buffer, @code{process-mark} returns a
1212 marker that points nowhere.
1214 Insertion of process output in a buffer uses this marker to decide where
1215 to insert, and updates it to point after the inserted text. That is why
1216 successive batches of output are inserted consecutively.
1218 Filter functions normally should use this marker in the same fashion
1219 as is done by direct insertion of output in the buffer. A good
1220 example of a filter function that uses @code{process-mark} is found at
1221 the end of the following section.
1223 When the user is expected to enter input in the process buffer for
1224 transmission to the process, the process marker separates the new input
1225 from previous output.
1228 @defun set-process-buffer process buffer
1229 This function sets the buffer associated with @var{process} to
1230 @var{buffer}. If @var{buffer} is @code{nil}, the process becomes
1231 associated with no buffer.
1234 @defun get-buffer-process buffer-or-name
1235 This function returns a nondeleted process associated with the buffer
1236 specified by @var{buffer-or-name}. If there are several processes
1237 associated with it, this function chooses one (currently, the one most
1238 recently created, but don't count on that). Deletion of a process
1239 (see @code{delete-process}) makes it ineligible for this function to
1242 It is usually a bad idea to have more than one process associated with
1247 (get-buffer-process "*shell*")
1248 @result{} #<process shell>
1252 Killing the process's buffer deletes the process, which kills the
1253 subprocess with a @code{SIGHUP} signal (@pxref{Signals to Processes}).
1256 @node Filter Functions
1257 @subsection Process Filter Functions
1258 @cindex filter function
1259 @cindex process filter
1261 A process @dfn{filter function} is a function that receives the
1262 standard output from the associated process. If a process has a filter,
1263 then @emph{all} output from that process is passed to the filter. The
1264 process buffer is used directly for output from the process only when
1267 The filter function can only be called when Emacs is waiting for
1268 something, because process output arrives only at such times. Emacs
1269 waits when reading terminal input, in @code{sit-for} and
1270 @code{sleep-for} (@pxref{Waiting}), and in @code{accept-process-output}
1271 (@pxref{Accepting Output}).
1273 A filter function must accept two arguments: the associated process
1274 and a string, which is output just received from it. The function is
1275 then free to do whatever it chooses with the output.
1277 Quitting is normally inhibited within a filter function---otherwise,
1278 the effect of typing @kbd{C-g} at command level or to quit a user
1279 command would be unpredictable. If you want to permit quitting inside
1280 a filter function, bind @code{inhibit-quit} to @code{nil}. In most
1281 cases, the right way to do this is with the macro
1282 @code{with-local-quit}. @xref{Quitting}.
1284 If an error happens during execution of a filter function, it is
1285 caught automatically, so that it doesn't stop the execution of whatever
1286 program was running when the filter function was started. However, if
1287 @code{debug-on-error} is non-@code{nil}, the error-catching is turned
1288 off. This makes it possible to use the Lisp debugger to debug the
1289 filter function. @xref{Debugger}.
1291 Many filter functions sometimes or always insert the text in the
1292 process's buffer, mimicking the actions of Emacs when there is no
1293 filter. Such filter functions need to use @code{set-buffer} in order to
1294 be sure to insert in that buffer. To avoid setting the current buffer
1295 semipermanently, these filter functions must save and restore the
1296 current buffer. They should also check whether the buffer is still
1297 alive, update the process marker, and in some cases update the value
1298 of point. Here is how to do these things:
1302 (defun ordinary-insertion-filter (proc string)
1303 (when (buffer-live-p (process-buffer proc))
1304 (with-current-buffer (process-buffer proc)
1305 (let ((moving (= (point) (process-mark proc))))
1309 ;; @r{Insert the text, advancing the process marker.}
1310 (goto-char (process-mark proc))
1312 (set-marker (process-mark proc) (point)))
1313 (if moving (goto-char (process-mark proc)))))))
1318 The reason to use @code{with-current-buffer}, rather than using
1319 @code{save-excursion} to save and restore the current buffer, is so as
1320 to preserve the change in point made by the second call to
1323 To make the filter force the process buffer to be visible whenever new
1324 text arrives, insert the following line just before the
1325 @code{with-current-buffer} construct:
1328 (display-buffer (process-buffer proc))
1331 To force point to the end of the new output, no matter where it was
1332 previously, eliminate the variable @code{moving} and call
1333 @code{goto-char} unconditionally.
1335 In earlier Emacs versions, every filter function that did regular
1336 expression searching or matching had to explicitly save and restore the
1337 match data. Now Emacs does this automatically for filter functions;
1338 they never need to do it explicitly. @xref{Match Data}.
1340 The output to the function may come in chunks of any size. A program
1341 that produces the same output twice in a row may send it as one batch of
1342 200 characters one time, and five batches of 40 characters the next. If
1343 the filter looks for certain text strings in the subprocess output, make
1344 sure to handle the case where one of these strings is split across two
1345 or more batches of output; one way to do this is to insert the
1346 received text into a temporary buffer, which can then be searched.
1348 @defun set-process-filter process filter
1349 This function gives @var{process} the filter function @var{filter}. If
1350 @var{filter} is @code{nil}, it gives the process no filter.
1353 @defun process-filter process
1354 This function returns the filter function of @var{process}, or @code{nil}
1358 Here is an example of use of a filter function:
1362 (defun keep-output (process output)
1363 (setq kept (cons output kept)))
1364 @result{} keep-output
1371 (set-process-filter (get-process "shell") 'keep-output)
1372 @result{} keep-output
1375 (process-send-string "shell" "ls ~/other\n")
1378 @result{} ("lewis@@slug[8] % "
1381 "FINAL-W87-SHORT.MSS backup.otl kolstad.mss~
1382 address.txt backup.psf kolstad.psf
1383 backup.bib~ david.mss resume-Dec-86.mss~
1384 backup.err david.psf resume-Dec.psf
1385 backup.mss dland syllabus.mss
1387 "#backups.mss# backup.mss~ kolstad.mss
1392 @ignore @c The code in this example doesn't show the right way to do things.
1393 Here is another, more realistic example, which demonstrates how to use
1394 the process mark to do insertion in the same fashion as is done when
1395 there is no filter function:
1399 ;; @r{Insert input in the buffer specified by @code{my-shell-buffer}}
1400 ;; @r{and make sure that buffer is shown in some window.}
1401 (defun my-process-filter (proc str)
1402 (let ((cur (selected-window))
1404 (pop-to-buffer my-shell-buffer)
1407 (goto-char (point-max))
1409 (set-marker (process-mark proc) (point-max))
1410 (select-window cur)))
1415 @node Decoding Output
1416 @subsection Decoding Process Output
1417 @cindex decode process output
1419 When Emacs writes process output directly into a multibyte buffer,
1420 it decodes the output according to the process output coding system.
1421 If the coding system is @code{raw-text} or @code{no-conversion}, Emacs
1422 converts the unibyte output to multibyte using
1423 @code{string-to-multibyte}, and inserts the resulting multibyte text.
1425 You can use @code{set-process-coding-system} to specify which coding
1426 system to use (@pxref{Process Information}). Otherwise, the coding
1427 system comes from @code{coding-system-for-read}, if that is
1428 non-@code{nil}; or else from the defaulting mechanism (@pxref{Default
1429 Coding Systems}). If the text output by a process contains null
1430 bytes, Emacs by default uses @code{no-conversion} for it; see
1431 @ref{Lisp and Coding Systems, inhibit-null-byte-detection}, for how to
1432 control this behavior.
1434 @strong{Warning:} Coding systems such as @code{undecided} which
1435 determine the coding system from the data do not work entirely
1436 reliably with asynchronous subprocess output. This is because Emacs
1437 has to process asynchronous subprocess output in batches, as it
1438 arrives. Emacs must try to detect the proper coding system from one
1439 batch at a time, and this does not always work. Therefore, if at all
1440 possible, specify a coding system that determines both the character
1441 code conversion and the end of line conversion---that is, one like
1442 @code{latin-1-unix}, rather than @code{undecided} or @code{latin-1}.
1444 @c Let's keep the index entries that were there for
1445 @c set-process-filter-multibyte and process-filter-multibyte-p,
1446 @cindex filter multibyte flag, of process
1447 @cindex process filter multibyte flag
1448 When Emacs calls a process filter function, it provides the process
1449 output as a multibyte string or as a unibyte string according to the
1450 process's filter coding system. Emacs
1451 decodes the output according to the process output coding system,
1452 which usually produces a multibyte string, except for coding systems
1453 such as @code{binary} and @code{raw-text}
1455 @node Accepting Output
1456 @subsection Accepting Output from Processes
1457 @cindex accept input from processes
1459 Output from asynchronous subprocesses normally arrives only while
1460 Emacs is waiting for some sort of external event, such as elapsed time
1461 or terminal input. Occasionally it is useful in a Lisp program to
1462 explicitly permit output to arrive at a specific point, or even to wait
1463 until output arrives from a process.
1465 @defun accept-process-output &optional process seconds millisec just-this-one
1466 This function allows Emacs to read pending output from processes. The
1467 output is inserted in the associated buffers or given to their filter
1468 functions. If @var{process} is non-@code{nil} then this function does
1469 not return until some output has been received from @var{process}.
1472 The arguments @var{seconds} and @var{millisec} let you specify timeout
1473 periods. The former specifies a period measured in seconds and the
1474 latter specifies one measured in milliseconds. The two time periods
1475 thus specified are added together, and @code{accept-process-output}
1476 returns after that much time, whether or not there has been any
1479 The argument @var{millisec} is semi-obsolete nowadays because
1480 @var{seconds} can be a floating point number to specify waiting a
1481 fractional number of seconds. If @var{seconds} is 0, the function
1482 accepts whatever output is pending but does not wait.
1484 @c Emacs 22.1 feature
1485 If @var{process} is a process, and the argument @var{just-this-one} is
1486 non-@code{nil}, only output from that process is handled, suspending output
1487 from other processes until some output has been received from that
1488 process or the timeout expires. If @var{just-this-one} is an integer,
1489 also inhibit running timers. This feature is generally not
1490 recommended, but may be necessary for specific applications, such as
1493 The function @code{accept-process-output} returns non-@code{nil} if it
1494 did get some output, or @code{nil} if the timeout expired before output
1499 @section Sentinels: Detecting Process Status Changes
1500 @cindex process sentinel
1501 @cindex sentinel (of process)
1503 A @dfn{process sentinel} is a function that is called whenever the
1504 associated process changes status for any reason, including signals
1505 (whether sent by Emacs or caused by the process's own actions) that
1506 terminate, stop, or continue the process. The process sentinel is
1507 also called if the process exits. The sentinel receives two
1508 arguments: the process for which the event occurred, and a string
1509 describing the type of event.
1511 The string describing the event looks like one of the following:
1515 @code{"finished\n"}.
1518 @code{"exited abnormally with code @var{exitcode}\n"}.
1521 @code{"@var{name-of-signal}\n"}.
1524 @code{"@var{name-of-signal} (core dumped)\n"}.
1527 A sentinel runs only while Emacs is waiting (e.g., for terminal
1528 input, or for time to elapse, or for process output). This avoids the
1529 timing errors that could result from running them at random places in
1530 the middle of other Lisp programs. A program can wait, so that
1531 sentinels will run, by calling @code{sit-for} or @code{sleep-for}
1532 (@pxref{Waiting}), or @code{accept-process-output} (@pxref{Accepting
1533 Output}). Emacs also allows sentinels to run when the command loop is
1534 reading input. @code{delete-process} calls the sentinel when it
1535 terminates a running process.
1537 Emacs does not keep a queue of multiple reasons to call the sentinel
1538 of one process; it records just the current status and the fact that
1539 there has been a change. Therefore two changes in status, coming in
1540 quick succession, can call the sentinel just once. However, process
1541 termination will always run the sentinel exactly once. This is
1542 because the process status can't change again after termination.
1544 Emacs explicitly checks for output from the process before running
1545 the process sentinel. Once the sentinel runs due to process
1546 termination, no further output can arrive from the process.
1548 A sentinel that writes the output into the buffer of the process
1549 should check whether the buffer is still alive. If it tries to insert
1550 into a dead buffer, it will get an error. If the buffer is dead,
1551 @code{(buffer-name (process-buffer @var{process}))} returns @code{nil}.
1553 Quitting is normally inhibited within a sentinel---otherwise, the
1554 effect of typing @kbd{C-g} at command level or to quit a user command
1555 would be unpredictable. If you want to permit quitting inside a
1556 sentinel, bind @code{inhibit-quit} to @code{nil}. In most cases, the
1557 right way to do this is with the macro @code{with-local-quit}.
1560 If an error happens during execution of a sentinel, it is caught
1561 automatically, so that it doesn't stop the execution of whatever
1562 programs was running when the sentinel was started. However, if
1563 @code{debug-on-error} is non-@code{nil}, the error-catching is turned
1564 off. This makes it possible to use the Lisp debugger to debug the
1565 sentinel. @xref{Debugger}.
1567 While a sentinel is running, the process sentinel is temporarily
1568 set to @code{nil} so that the sentinel won't run recursively.
1569 For this reason it is not possible for a sentinel to specify
1572 In earlier Emacs versions, every sentinel that did regular expression
1573 searching or matching had to explicitly save and restore the match data.
1574 Now Emacs does this automatically for sentinels; they never need to do
1575 it explicitly. @xref{Match Data}.
1577 @defun set-process-sentinel process sentinel
1578 This function associates @var{sentinel} with @var{process}. If
1579 @var{sentinel} is @code{nil}, then the process will have no sentinel.
1580 The default behavior when there is no sentinel is to insert a message in
1581 the process's buffer when the process status changes.
1583 Changes in process sentinel take effect immediately---if the sentinel
1584 is slated to be run but has not been called yet, and you specify a new
1585 sentinel, the eventual call to the sentinel will use the new one.
1589 (defun msg-me (process event)
1591 (format "Process: %s had the event `%s'" process event)))
1592 (set-process-sentinel (get-process "shell") 'msg-me)
1596 (kill-process (get-process "shell"))
1597 @print{} Process: #<process shell> had the event `killed'
1598 @result{} #<process shell>
1603 @defun process-sentinel process
1604 This function returns the sentinel of @var{process}, or @code{nil} if it
1608 @defun waiting-for-user-input-p
1609 While a sentinel or filter function is running, this function returns
1610 non-@code{nil} if Emacs was waiting for keyboard input from the user at
1611 the time the sentinel or filter function was called, @code{nil} if it
1615 @node Query Before Exit
1616 @section Querying Before Exit
1618 When Emacs exits, it terminates all its subprocesses by sending them
1619 the @code{SIGHUP} signal. Because subprocesses may be doing
1620 valuable work, Emacs normally asks the user to confirm that it is ok
1621 to terminate them. Each process has a query flag which, if
1622 non-@code{nil}, says that Emacs should ask for confirmation before
1623 exiting and thus killing that process. The default for the query flag
1624 is @code{t}, meaning @emph{do} query.
1626 @defun process-query-on-exit-flag process
1627 This returns the query flag of @var{process}.
1630 @defun set-process-query-on-exit-flag process flag
1631 This function sets the query flag of @var{process} to @var{flag}. It
1634 Here is an example of using @code{set-process-query-on-exit-flag} on a
1635 shell process to avoid querying:
1639 (set-process-query-on-exit-flag (get-process "shell") nil)
1645 @node System Processes
1646 @section Accessing Other Processes
1647 @cindex system processes
1649 In addition to accessing and manipulating processes that are
1650 subprocesses of the current Emacs session, Emacs Lisp programs can
1651 also access other processes running on the same machine. We call
1652 these @dfn{system processes}, to distinguish between them and Emacs
1655 Emacs provides several primitives for accessing system processes.
1656 Not all platforms support these primitives; on those which don't,
1657 these primitives return @code{nil}.
1659 @defun list-system-processes
1660 This function returns a list of all the processes running on the
1661 system. Each process is identified by its @acronym{PID}, a numerical
1662 process ID that is assigned by the OS and distinguishes the process
1663 from all the other processes running on the same machine at the same
1667 @defun process-attributes pid
1668 This function returns an alist of attributes for the process specified
1669 by its process ID @var{pid}. Each association in the alist is of the
1670 form @code{(@var{key} . @var{value})}, where @var{key} designates the
1671 attribute and @var{value} is the value of that attribute. The various
1672 attribute @var{key}'s that this function can return are listed below.
1673 Not all platforms support all of these attributes; if an attribute is
1674 not supported, its association will not appear in the returned alist.
1675 Values that are numbers can be either integer or floating-point,
1676 depending on the magnitude of the value.
1680 The effective user ID of the user who invoked the process. The
1681 corresponding @var{value} is a number. If the process was invoked by
1682 the same user who runs the current Emacs session, the value is
1683 identical to what @code{user-uid} returns (@pxref{User
1687 User name corresponding to the process's effective user ID, a string.
1690 The group ID of the effective user ID, a number.
1693 Group name corresponding to the effective user's group ID, a string.
1696 The name of the command that runs in the process. This is a string
1697 that usually specifies the name of the executable file of the process,
1698 without the leading directories. However, some special system
1699 processes can report strings that do not correspond to an executable
1703 The state code of the process. This is a short string that encodes
1704 the scheduling state of the process. Here's a list of the most
1705 frequently seen codes:
1709 uninterruptible sleep (usually I/O)
1713 interruptible sleep (waiting for some event)
1715 stopped, e.g., by a job control signal
1717 ``zombie'': a process that terminated, but was not reaped by its parent
1721 For the full list of the possible states, see the manual page of the
1722 @command{ps} command.
1725 The process ID of the parent process, a number.
1728 The process group ID of the process, a number.
1731 The session ID of the process. This is a number that is the process
1732 ID of the process's @dfn{session leader}.
1735 A string that is the name of the process's controlling terminal. On
1736 Unix and GNU systems, this is normally the file name of the
1737 corresponding terminal device, such as @file{/dev/pts65}.
1740 The numerical process group ID of the foreground process group that
1741 uses the process's terminal.
1744 The number of minor page faults caused by the process since its
1745 beginning. (Minor page faults are those that don't involve reading
1749 The number of major page faults caused by the process since its
1750 beginning. (Major page faults require a disk to be read, and are thus
1751 more expensive than minor page faults.)
1755 Like @code{minflt} and @code{majflt}, but include the number of page
1756 faults for all the child processes of the given process.
1759 Time spent by the process in the user context, for running the
1760 application's code. The corresponding @var{value} is in the
1761 @w{@code{(@var{high} @var{low} @var{microsec})}} format, the same
1762 format used by functions @code{current-time} (@pxref{Time of Day,
1763 current-time}) and @code{file-attributes} (@pxref{File Attributes}).
1766 Time spent by the process in the system (kernel) context, for
1767 processing system calls. The corresponding @var{value} is in the same
1768 format as for @code{utime}.
1771 The sum of @code{utime} and @code{stime}. The corresponding
1772 @var{value} is in the same format as for @code{utime}.
1777 Like @code{utime}, @code{stime}, and @code{time}, but include the
1778 times of all the child processes of the given process.
1781 The numerical priority of the process.
1784 The @dfn{nice value} of the process, a number. (Processes with smaller
1785 nice values get scheduled more favorably.)
1788 The number of threads in the process.
1791 The time when the process was started, in the same
1792 @w{@code{(@var{high} @var{low} @var{microsec})}} format used by
1793 @code{current-time} and @code{file-attributes}.
1796 The time elapsed since the process started, in the @w{@code{(@var{high}
1797 @var{low} @var{microsec})}} format.
1800 The virtual memory size of the process, measured in kilobytes.
1803 The size of the process's @dfn{resident set}, the number of kilobytes
1804 occupied by the process in the machine's physical memory.
1807 The percentage of the CPU time used by the process since it started.
1808 The corresponding @var{value} is a floating-point number between 0 and
1812 The percentage of the total physical memory installed on the machine
1813 used by the process's resident set. The value is a floating-point
1814 number between 0 and 100.
1817 The command-line with which the process was invoked. This is a string
1818 in which individual command-line arguments are separated by blanks;
1819 whitespace characters that are embedded in the arguments are quoted as
1820 appropriate for the system's shell: escaped by backslash characters on
1821 GNU and Unix, and enclosed in double quote characters on Windows.
1822 Thus, this command-line string can be directly used in primitives such
1823 as @code{shell-command}.
1829 @node Transaction Queues
1830 @section Transaction Queues
1831 @cindex transaction queue
1833 You can use a @dfn{transaction queue} to communicate with a subprocess
1834 using transactions. First use @code{tq-create} to create a transaction
1835 queue communicating with a specified process. Then you can call
1836 @code{tq-enqueue} to send a transaction.
1838 @defun tq-create process
1839 This function creates and returns a transaction queue communicating with
1840 @var{process}. The argument @var{process} should be a subprocess
1841 capable of sending and receiving streams of bytes. It may be a child
1842 process, or it may be a TCP connection to a server, possibly on another
1846 @defun tq-enqueue queue question regexp closure fn &optional delay-question
1847 This function sends a transaction to queue @var{queue}. Specifying the
1848 queue has the effect of specifying the subprocess to talk to.
1850 The argument @var{question} is the outgoing message that starts the
1851 transaction. The argument @var{fn} is the function to call when the
1852 corresponding answer comes back; it is called with two arguments:
1853 @var{closure}, and the answer received.
1855 The argument @var{regexp} is a regular expression that should match
1856 text at the end of the entire answer, but nothing before; that's how
1857 @code{tq-enqueue} determines where the answer ends.
1859 If the argument @var{delay-question} is non-@code{nil}, delay sending
1860 this question until the process has finished replying to any previous
1861 questions. This produces more reliable results with some processes.
1863 The return value of @code{tq-enqueue} itself is not meaningful.
1866 @defun tq-close queue
1867 Shut down transaction queue @var{queue}, waiting for all pending transactions
1868 to complete, and then terminate the connection or child process.
1871 Transaction queues are implemented by means of a filter function.
1872 @xref{Filter Functions}.
1875 @section Network Connections
1876 @cindex network connection
1880 Emacs Lisp programs can open stream (TCP) and datagram (UDP) network
1881 connections to other processes on the same machine or other machines.
1882 A network connection is handled by Lisp much like a subprocess, and is
1883 represented by a process object. However, the process you are
1884 communicating with is not a child of the Emacs process, so it has no
1885 process @acronym{ID}, and you can't kill it or send it signals. All you
1886 can do is send and receive data. @code{delete-process} closes the
1887 connection, but does not kill the program at the other end; that
1888 program must decide what to do about closure of the connection.
1890 Lisp programs can listen for connections by creating network
1891 servers. A network server is also represented by a kind of process
1892 object, but unlike a network connection, the network server never
1893 transfers data itself. When it receives a connection request, it
1894 creates a new network connection to represent the connection just
1895 made. (The network connection inherits certain information, including
1896 the process plist, from the server.) The network server then goes
1897 back to listening for more connection requests.
1899 Network connections and servers are created by calling
1900 @code{make-network-process} with an argument list consisting of
1901 keyword/argument pairs, for example @code{:server t} to create a
1902 server process, or @code{:type 'datagram} to create a datagram
1903 connection. @xref{Low-Level Network}, for details. You can also use
1904 the @code{open-network-stream} function described below.
1906 To distinguish the different types of processes, the
1907 @code{process-type} function returns the symbol @code{network} for a
1908 network connection or server, @code{serial} for a serial port
1909 connection, or @code{real} for a real subprocess.
1911 The @code{process-status} function returns @code{open},
1912 @code{closed}, @code{connect}, and @code{failed} for network
1913 connections. For a network server, the status is always
1914 @code{listen}. None of those values is possible for a real
1915 subprocess. @xref{Process Information}.
1917 You can stop and resume operation of a network process by calling
1918 @code{stop-process} and @code{continue-process}. For a server
1919 process, being stopped means not accepting new connections. (Up to 5
1920 connection requests will be queued for when you resume the server; you
1921 can increase this limit, unless it is imposed by the operating
1922 system.) For a network stream connection, being stopped means not
1923 processing input (any arriving input waits until you resume the
1924 connection). For a datagram connection, some number of packets may be
1925 queued but input may be lost. You can use the function
1926 @code{process-command} to determine whether a network connection or
1927 server is stopped; a non-@code{nil} value means yes.
1929 @cindex network connection, encrypted
1930 @cindex encrypted network connections
1931 @cindex TLS network connections
1932 @cindex STARTTLS network connections
1933 @defun open-network-stream name buffer-or-name host service &rest parameters
1934 This function opens a TCP connection, with optional encryption, and
1935 returns a process object that represents the connection.
1937 The @var{name} argument specifies the name for the process object. It
1938 is modified as necessary to make it unique.
1940 The @var{buffer-or-name} argument is the buffer to associate with the
1941 connection. Output from the connection is inserted in the buffer,
1942 unless you specify a filter function to handle the output. If
1943 @var{buffer-or-name} is @code{nil}, it means that the connection is not
1944 associated with any buffer.
1946 The arguments @var{host} and @var{service} specify where to connect to;
1947 @var{host} is the host name (a string), and @var{service} is the name of
1948 a defined network service (a string) or a port number (an integer).
1950 @c FIXME? Is this too lengthy for the printed manual?
1951 The remaining arguments @var{parameters} are keyword/argument pairs
1952 that are mainly relevant to encrypted connections:
1956 @item :nowait @var{boolean}
1957 If non-@code{nil}, try to make an asynchronous connection.
1959 @item :type @var{type}
1960 The type of connection. Options are:
1964 An ordinary, unencrypted connection.
1967 A TLS (``Transport Layer Security'') connection.
1970 Start with a plain connection, and if parameters @samp{:success}
1971 and @samp{:capability-command} are supplied, try to upgrade to an encrypted
1972 connection via STARTTLS. If that fails, retain the unencrypted connection.
1974 As for @code{nil}, but if STARTTLS fails drop the connection.
1979 @item :always-query-capabilities @var{boolean}
1980 If non-@code{nil}, always ask for the server's capabilities, even when
1981 doing a @samp{plain} connection.
1983 @item :capability-command @var{capability-command}
1984 Command string to query the host capabilities.
1986 @item :end-of-command @var{regexp}
1987 @itemx :end-of-capability @var{regexp}
1988 Regular expression matching the end of a command, or the end of the
1989 command @var{capability-command}. The latter defaults to the former.
1991 @item :starttls-function @var{function}
1992 Function of one argument (the response to @var{capability-command}),
1993 which returns either @code{nil}, or the command to activate STARTTLS
1996 @item :success @var{regexp}
1997 Regular expression matching a successful STARTTLS negotiation.
1999 @item :use-starttls-if-possible @var{boolean}
2000 If non-@code{nil}, do opportunistic STARTTLS upgrades even if Emacs
2001 doesn't have built-in TLS support.
2003 @item :client-certificate @var{list-or-t}
2004 Either a list of the form @code{(@var{key-file} @var{cert-file})},
2005 naming the certificate key file and certificate file itself, or
2006 @code{t}, meaning to query @code{auth-source} for this information
2007 (@pxref{Top,,auth-source, auth, Emacs auth-source Library}).
2008 Only used for TLS or STARTTLS.
2010 @item :return-list @var{cons-or-nil}
2011 The return value of this function. If omitted or @code{nil}, return a
2012 process object. Otherwise, a cons of the form @code{(@var{process-object}
2013 . @var{plist})}, where @var{plist} has keywords:
2016 @item :greeting @var{string-or-nil}
2017 If non-@code{nil}, the greeting string returned by the host.
2018 @item :capabilities @var{string-or-nil}
2019 If non-@code{nil}, the host's capability string.
2020 @item :type @var{symbol}
2021 The connection type: @samp{plain} or @samp{tls}.
2028 @node Network Servers
2029 @section Network Servers
2030 @cindex network servers
2032 You create a server by calling @code{make-network-process} with
2033 @code{:server t}. The server will listen for connection requests from
2034 clients. When it accepts a client connection request, that creates a
2035 new network connection, itself a process object, with the following
2040 The connection's process name is constructed by concatenating the
2041 server process's @var{name} with a client identification string. The
2042 client identification string for an IPv4 connection looks like
2043 @samp{<@var{a}.@var{b}.@var{c}.@var{d}:@var{p}>}. Otherwise, it is a
2044 unique number in brackets, as in @samp{<@var{nnn}>}. The number
2045 is unique for each connection in the Emacs session.
2048 If the server's filter is non-@code{nil}, the connection process does
2049 not get a separate process buffer; otherwise, Emacs creates a new
2050 buffer for the purpose. The buffer name is the server's buffer name
2051 or process name, concatenated with the client identification string.
2053 The server's process buffer value is never used directly, but the log
2054 function can retrieve it and use it to log connections by inserting
2058 The communication type and the process filter and sentinel are
2059 inherited from those of the server. The server never directly
2060 uses its filter and sentinel; their sole purpose is to initialize
2061 connections made to the server.
2064 The connection's process contact info is set according to the client's
2065 addressing information (typically an IP address and a port number).
2066 This information is associated with the @code{process-contact}
2067 keywords @code{:host}, @code{:service}, @code{:remote}.
2070 The connection's local address is set up according to the port
2071 number used for the connection.
2074 The client process's plist is initialized from the server's plist.
2081 A datagram connection communicates with individual packets rather
2082 than streams of data. Each call to @code{process-send} sends one
2083 datagram packet (@pxref{Input to Processes}), and each datagram
2084 received results in one call to the filter function.
2086 The datagram connection doesn't have to talk with the same remote
2087 peer all the time. It has a @dfn{remote peer address} which specifies
2088 where to send datagrams to. Each time an incoming datagram is passed
2089 to the filter function, the peer address is set to the address that
2090 datagram came from; that way, if the filter function sends a datagram,
2091 it will go back to that place. You can specify the remote peer
2092 address when you create the datagram connection using the
2093 @code{:remote} keyword. You can change it later on by calling
2094 @code{set-process-datagram-address}.
2096 @defun process-datagram-address process
2097 If @var{process} is a datagram connection or server, this function
2098 returns its remote peer address.
2101 @defun set-process-datagram-address process address
2102 If @var{process} is a datagram connection or server, this function
2103 sets its remote peer address to @var{address}.
2106 @node Low-Level Network
2107 @section Low-Level Network Access
2109 You can also create network connections by operating at a lower
2110 level than that of @code{open-network-stream}, using
2111 @code{make-network-process}.
2114 * Proc: Network Processes. Using @code{make-network-process}.
2115 * Options: Network Options. Further control over network connections.
2116 * Features: Network Feature Testing.
2117 Determining which network features work on
2118 the machine you are using.
2121 @node Network Processes
2122 @subsection @code{make-network-process}
2124 The basic function for creating network connections and network
2125 servers is @code{make-network-process}. It can do either of those
2126 jobs, depending on the arguments you give it.
2128 @defun make-network-process &rest args
2129 This function creates a network connection or server and returns the
2130 process object that represents it. The arguments @var{args} are a
2131 list of keyword/argument pairs. Omitting a keyword is always
2132 equivalent to specifying it with value @code{nil}, except for
2133 @code{:coding}, @code{:filter-multibyte}, and @code{:reuseaddr}. Here
2134 are the meaningful keywords:
2137 @item :name @var{name}
2138 Use the string @var{name} as the process name. It is modified if
2139 necessary to make it unique.
2141 @item :type @var{type}
2142 Specify the communication type. A value of @code{nil} specifies a
2143 stream connection (the default); @code{datagram} specifies a datagram
2144 connection; @code{seqpacket} specifies a ``sequenced packet stream''
2145 connection. Both connections and servers can be of these types.
2147 @item :server @var{server-flag}
2148 If @var{server-flag} is non-@code{nil}, create a server. Otherwise,
2149 create a connection. For a stream type server, @var{server-flag} may
2150 be an integer which then specifies the length of the queue of pending
2151 connections to the server. The default queue length is 5.
2153 @item :host @var{host}
2154 Specify the host to connect to. @var{host} should be a host name or
2155 Internet address, as a string, or the symbol @code{local} to specify
2156 the local host. If you specify @var{host} for a server, it must
2157 specify a valid address for the local host, and only clients
2158 connecting to that address will be accepted.
2160 @item :service @var{service}
2161 @var{service} specifies a port number to connect to, or, for a server,
2162 the port number to listen on. It should be a service name that
2163 translates to a port number, or an integer specifying the port number
2164 directly. For a server, it can also be @code{t}, which means to let
2165 the system select an unused port number.
2167 @item :family @var{family}
2168 @var{family} specifies the address (and protocol) family for
2169 communication. @code{nil} means determine the proper address family
2170 automatically for the given @var{host} and @var{service}.
2171 @code{local} specifies a Unix socket, in which case @var{host} is
2172 ignored. @code{ipv4} and @code{ipv6} specify to use IPv4 and IPv6
2175 @item :local @var{local-address}
2176 For a server process, @var{local-address} is the address to listen on.
2177 It overrides @var{family}, @var{host} and @var{service}, and you
2178 may as well not specify them.
2180 @item :remote @var{remote-address}
2181 For a connection, @var{remote-address} is the address to connect to.
2182 It overrides @var{family}, @var{host} and @var{service}, and you
2183 may as well not specify them.
2185 For a datagram server, @var{remote-address} specifies the initial
2186 setting of the remote datagram address.
2188 The format of @var{local-address} or @var{remote-address} depends on
2193 An IPv4 address is represented as a five-element vector of four 8-bit
2194 integers and one 16-bit integer
2195 @code{[@var{a} @var{b} @var{c} @var{d} @var{p}]} corresponding to
2196 numeric IPv4 address @var{a}.@var{b}.@var{c}.@var{d} and port number
2200 An IPv6 address is represented as a nine-element vector of 16-bit
2201 integers @code{[@var{a} @var{b} @var{c} @var{d} @var{e} @var{f}
2202 @var{g} @var{h} @var{p}]} corresponding to numeric IPv6 address
2203 @var{a}:@var{b}:@var{c}:@var{d}:@var{e}:@var{f}:@var{g}:@var{h} and
2204 port number @var{p}.
2207 A local address is represented as a string which specifies the address
2208 in the local address space.
2211 An ``unsupported family'' address is represented by a cons
2212 @code{(@var{f} . @var{av})}, where @var{f} is the family number and
2213 @var{av} is a vector specifying the socket address using one element
2214 per address data byte. Do not rely on this format in portable code,
2215 as it may depend on implementation defined constants, data sizes, and
2216 data structure alignment.
2219 @item :nowait @var{bool}
2220 If @var{bool} is non-@code{nil} for a stream connection, return
2221 without waiting for the connection to complete. When the connection
2222 succeeds or fails, Emacs will call the sentinel function, with a
2223 second argument matching @code{"open"} (if successful) or
2224 @code{"failed"}. The default is to block, so that
2225 @code{make-network-process} does not return until the connection
2226 has succeeded or failed.
2228 @item :stop @var{stopped}
2229 Start the network connection or server in the `stopped' state if
2230 @var{stopped} is non-@code{nil}.
2232 @item :buffer @var{buffer}
2233 Use @var{buffer} as the process buffer.
2235 @item :coding @var{coding}
2236 Use @var{coding} as the coding system for this process. To specify
2237 different coding systems for decoding data from the connection and for
2238 encoding data sent to it, specify @code{(@var{decoding} .
2239 @var{encoding})} for @var{coding}.
2241 If you don't specify this keyword at all, the default
2242 is to determine the coding systems from the data.
2244 @item :noquery @var{query-flag}
2245 Initialize the process query flag to @var{query-flag}.
2246 @xref{Query Before Exit}.
2248 @item :filter @var{filter}
2249 Initialize the process filter to @var{filter}.
2251 @item :sentinel @var{sentinel}
2252 Initialize the process sentinel to @var{sentinel}.
2254 @item :log @var{log}
2255 Initialize the log function of a server process to @var{log}. The log
2256 function is called each time the server accepts a network connection
2257 from a client. The arguments passed to the log function are
2258 @var{server}, @var{connection}, and @var{message}, where @var{server}
2259 is the server process, @var{connection} is the new process for the
2260 connection, and @var{message} is a string describing what has
2263 @item :plist @var{plist}
2264 Initialize the process plist to @var{plist}.
2267 The original argument list, modified with the actual connection
2268 information, is available via the @code{process-contact} function.
2271 @node Network Options
2272 @subsection Network Options
2274 The following network options can be specified when you create a
2275 network process. Except for @code{:reuseaddr}, you can also set or
2276 modify these options later, using @code{set-network-process-option}.
2278 For a server process, the options specified with
2279 @code{make-network-process} are not inherited by the client
2280 connections, so you will need to set the necessary options for each
2281 child connection as it is created.
2284 @item :bindtodevice @var{device-name}
2285 If @var{device-name} is a non-empty string identifying a network
2286 interface name (see @code{network-interface-list}), only handle
2287 packets received on that interface. If @var{device-name} is @code{nil}
2288 (the default), handle packets received on any interface.
2290 Using this option may require special privileges on some systems.
2292 @item :broadcast @var{broadcast-flag}
2293 If @var{broadcast-flag} is non-@code{nil} for a datagram process, the
2294 process will receive datagram packet sent to a broadcast address, and
2295 be able to send packets to a broadcast address. Ignored for a stream
2298 @item :dontroute @var{dontroute-flag}
2299 If @var{dontroute-flag} is non-@code{nil}, the process can only send
2300 to hosts on the same network as the local host.
2302 @item :keepalive @var{keepalive-flag}
2303 If @var{keepalive-flag} is non-@code{nil} for a stream connection,
2304 enable exchange of low-level keep-alive messages.
2306 @item :linger @var{linger-arg}
2307 If @var{linger-arg} is non-@code{nil}, wait for successful
2308 transmission of all queued packets on the connection before it is
2309 deleted (see @code{delete-process}). If @var{linger-arg} is an
2310 integer, it specifies the maximum time in seconds to wait for queued
2311 packets to be sent before closing the connection. Default is
2312 @code{nil} which means to discard unsent queued packets when the
2315 @item :oobinline @var{oobinline-flag}
2316 If @var{oobinline-flag} is non-@code{nil} for a stream connection,
2317 receive out-of-band data in the normal data stream. Otherwise, ignore
2320 @item :priority @var{priority}
2321 Set the priority for packets sent on this connection to the integer
2322 @var{priority}. The interpretation of this number is protocol
2323 specific, such as setting the TOS (type of service) field on IP
2324 packets sent on this connection. It may also have system dependent
2325 effects, such as selecting a specific output queue on the network
2328 @item :reuseaddr @var{reuseaddr-flag}
2329 If @var{reuseaddr-flag} is non-@code{nil} (the default) for a stream
2330 server process, allow this server to reuse a specific port number (see
2331 @code{:service}) unless another process on this host is already
2332 listening on that port. If @var{reuseaddr-flag} is @code{nil}, there
2333 may be a period of time after the last use of that port (by any
2334 process on the host), where it is not possible to make a new server on
2338 @defun set-network-process-option process option value &optional no-error
2339 This function sets or modifies a network option for network process
2340 @var{process}. See @code{make-network-process} for details of options
2341 @var{option} and their corresponding values @var{value}. If
2342 @var{no-error} is non-@code{nil}, this function returns @code{nil}
2343 instead of signaling an error if @var{option} is not a supported
2344 option. If the function successfully completes, it returns @code{t}.
2346 The current setting of an option is available via the
2347 @code{process-contact} function.
2350 @node Network Feature Testing
2351 @subsection Testing Availability of Network Features
2353 To test for the availability of a given network feature, use
2354 @code{featurep} like this:
2357 (featurep 'make-network-process '(@var{keyword} @var{value}))
2361 The result of the first form is @code{t} if it works to specify
2362 @var{keyword} with value @var{value} in @code{make-network-process}.
2363 The result of the second form is @code{t} if @var{keyword} is
2364 supported by @code{make-network-process}. Here are some of the
2365 @var{keyword}---@var{value} pairs you can test in
2370 Non-@code{nil} if non-blocking connect is supported.
2371 @item (:type datagram)
2372 Non-@code{nil} if datagrams are supported.
2373 @item (:family local)
2374 Non-@code{nil} if local (a.k.a.@: ``UNIX domain'') sockets are supported.
2375 @item (:family ipv6)
2376 Non-@code{nil} if IPv6 is supported.
2378 Non-@code{nil} if the system can select the port for a server.
2381 To test for the availability of a given network option, use
2382 @code{featurep} like this:
2385 (featurep 'make-network-process '@var{keyword})
2389 Here are some of the options you can test in this way.
2400 That particular network option is supported by
2401 @code{make-network-process} and @code{set-network-process-option}.
2405 @section Misc Network Facilities
2407 These additional functions are useful for creating and operating
2408 on network connections. Note that they are supported only on some
2411 @defun network-interface-list
2412 This function returns a list describing the network interfaces
2413 of the machine you are using. The value is an alist whose
2414 elements have the form @code{(@var{name} . @var{address})}.
2415 @var{address} has the same form as the @var{local-address}
2416 and @var{remote-address} arguments to @code{make-network-process}.
2419 @defun network-interface-info ifname
2420 This function returns information about the network interface named
2421 @var{ifname}. The value is a list of the form
2422 @code{(@var{addr} @var{bcast} @var{netmask} @var{hwaddr} @var{flags})}.
2426 The Internet protocol address.
2428 The broadcast address.
2432 The layer 2 address (Ethernet MAC address, for instance).
2434 The current flags of the interface.
2438 @defun format-network-address address &optional omit-port
2439 This function converts the Lisp representation of a network address to
2442 A five-element vector @code{[@var{a} @var{b} @var{c} @var{d} @var{p}]}
2443 represents an IPv4 address @var{a}.@var{b}.@var{c}.@var{d} and port
2444 number @var{p}. @code{format-network-address} converts that to the
2445 string @code{"@var{a}.@var{b}.@var{c}.@var{d}:@var{p}"}.
2447 A nine-element vector @code{[@var{a} @var{b} @var{c} @var{d} @var{e}
2448 @var{f} @var{g} @var{h} @var{p}]} represents an IPv6 address along
2449 with a port number. @code{format-network-address} converts that to
2451 @code{"[@var{a}:@var{b}:@var{c}:@var{d}:@var{e}:@var{f}:@var{g}:@var{h}]:@var{p}"}.
2453 If the vector does not include the port number, @var{p}, or if
2454 @var{omit-port} is non-@code{nil}, the result does not include the
2455 @code{:@var{p}} suffix.
2459 @section Communicating with Serial Ports
2460 @cindex @file{/dev/tty}
2462 @cindex serial connections
2464 Emacs can communicate with serial ports. For interactive use,
2465 @kbd{M-x serial-term} opens a terminal window. In a Lisp program,
2466 @code{make-serial-process} creates a process object.
2468 The serial port can be configured at run-time, without having to
2469 close and re-open it. The function @code{serial-process-configure}
2470 lets you change the speed, bytesize, and other parameters. In a
2471 terminal window created by @code{serial-term}, you can click on the
2472 mode line for configuration.
2474 A serial connection is represented by a process object which can be
2475 used similar to a subprocess or network process. You can send and
2476 receive data and configure the serial port. A serial process object
2477 has no process ID, you can't send signals to it, and the status codes
2478 are different from other types of processes.
2479 @code{delete-process} on the process object or @code{kill-buffer} on
2480 the process buffer close the connection, but this does not affect the
2481 device connected to the serial port.
2483 The function @code{process-type} returns the symbol @code{serial}
2484 for a process object representing a serial port connection.
2486 Serial ports are available on GNU/Linux, Unix, and Windows systems.
2488 @deffn Command serial-term port speed
2489 Start a terminal-emulator for a serial port in a new buffer.
2490 @var{port} is the name of the serial port to which to connect. For
2491 example, this could be @file{/dev/ttyS0} on Unix. On Windows, this
2492 could be @file{COM1}, or @file{\\.\COM10} (double the backslashes in
2495 @var{speed} is the speed of the serial port in bits per second. 9600
2496 is a common value. The buffer is in Term mode; see @ref{Term Mode,,,
2497 emacs, The GNU Emacs Manual}, for the commands to use in that buffer.
2498 You can change the speed and the configuration in the mode line menu.
2501 @defun make-serial-process &rest args
2502 This function creates a process and a buffer. Arguments are specified
2503 as keyword/argument pairs. Here's the list of the meaningful keywords:
2506 @item :port @var{port}@r{ (mandatory)}
2507 This is the name of the serial port. On Unix and GNU systems, this is
2508 a file name such as @file{/dev/ttyS0}. On Windows, this could be
2509 @file{COM1}, or @file{\\.\COM10} for ports higher than @file{COM9}
2510 (double the backslashes in Lisp strings).
2512 @item :speed @var{speed}@r{ (mandatory)}
2513 The speed of the serial port in bits per second. This function calls
2514 @code{serial-process-configure} to handle the speed.
2516 @item :name @var{name}
2517 The name of the process. If @var{name} is not given, @var{port} will
2518 serve as the process name as well.
2520 @item :buffer @var{buffer}
2521 The buffer to associate with the process. The value could be either a
2522 buffer or a string that names a buffer. Process output goes at the
2523 end of that buffer, unless you specify an output stream or filter
2524 function to handle the output. If @var{buffer} is not given, the
2525 process buffer's name is taken from the value of the @code{:name}
2528 @item :coding @var{coding}
2529 If @var{coding} is a symbol, it specifies the coding system used for
2530 both reading and writing for this process. If @var{coding} is a cons
2531 @code{(decoding . encoding)}, @var{decoding} is used for reading, and
2532 @var{encoding} is used for writing. If not specified, the default is
2533 to determine the coding systems from data itself.
2535 @item :noquery @var{query-flag}
2536 Initialize the process query flag to @var{query-flag}. @xref{Query
2537 Before Exit}. The flags defaults to @code{nil} if unspecified.
2539 @item :stop @var{bool}
2540 Start process in the @code{stopped} state if @var{bool} is
2541 non-@code{nil}. In the stopped state, a serial process does not
2542 accept incoming data, but you can send outgoing data. The stopped
2543 state is cleared by @code{continue-process} and set by
2544 @code{stop-process}.
2546 @item :filter @var{filter}
2547 Install @var{filter} as the process filter.
2549 @item :sentinel @var{sentinel}
2550 Install @var{sentinel} as the process sentinel.
2552 @item :plist @var{plist}
2553 Install @var{plist} as the initial plist of the process.
2560 These are handled by @code{serial-process-configure}, which is called
2561 by @code{make-serial-process}.
2564 The original argument list, possibly modified by later configuration,
2565 is available via the function @code{process-contact}.
2570 (make-serial-process :port "/dev/ttyS0" :speed 9600)
2574 @defun serial-process-configure &rest args
2575 @cindex baud, in serial connections
2576 @cindex bytesize, in serial connections
2577 @cindex parity, in serial connections
2578 @cindex stopbits, in serial connections
2579 @cindex flowcontrol, in serial connections
2581 This functions configures a serial port connection. Arguments are
2582 specified as keyword/argument pairs. Attributes that are not given
2583 are re-initialized from the process's current configuration (available
2584 via the function @code{process-contact}) or set to reasonable default
2585 values. The following arguments are defined:
2588 @item :process @var{process}
2589 @itemx :name @var{name}
2590 @itemx :buffer @var{buffer}
2591 @itemx :port @var{port}
2592 Any of these arguments can be given to identify the process that is to
2593 be configured. If none of these arguments is given, the current
2594 buffer's process is used.
2596 @item :speed @var{speed}
2597 The speed of the serial port in bits per second, a.k.a.@: @dfn{baud
2598 rate}. The value can be any number, but most serial ports work only
2599 at a few defined values between 1200 and 115200, with 9600 being the
2600 most common value. If @var{speed} is @code{nil}, the function ignores
2601 all other arguments and does not configure the port. This may be
2602 useful for special serial ports such as Bluetooth-to-serial converters
2603 which can only be configured through AT commands sent through the
2604 connection. The value of @code{nil} for @var{speed} is valid only for
2605 connections that were already opened by a previous call to
2606 @code{make-serial-process} or @code{serial-term}.
2608 @item :bytesize @var{bytesize}
2609 The number of bits per byte, which can be 7 or 8. If @var{bytesize}
2610 is not given or @code{nil}, it defaults to 8.
2612 @item :parity @var{parity}
2613 The value can be @code{nil} (don't use parity), the symbol
2614 @code{odd} (use odd parity), or the symbol @code{even} (use even
2615 parity). If @var{parity} is not given, it defaults to no parity.
2617 @item :stopbits @var{stopbits}
2618 The number of stopbits used to terminate a transmission
2619 of each byte. @var{stopbits} can be 1 or 2. If @var{stopbits} is not
2620 given or @code{nil}, it defaults to 1.
2622 @item :flowcontrol @var{flowcontrol}
2623 The type of flow control to use for this connection, which is either
2624 @code{nil} (don't use flow control), the symbol @code{hw} (use RTS/CTS
2625 hardware flow control), or the symbol @code{sw} (use XON/XOFF software
2626 flow control). If @var{flowcontrol} is not given, it defaults to no
2630 @code{serial-process-configure} is called by
2631 @code{make-serial-process} for the initial configuration of the serial
2636 @section Packing and Unpacking Byte Arrays
2637 @cindex byte packing and unpacking
2639 This section describes how to pack and unpack arrays of bytes,
2640 usually for binary network protocols. These functions convert byte arrays
2641 to alists, and vice versa. The byte array can be represented as a
2642 unibyte string or as a vector of integers, while the alist associates
2643 symbols either with fixed-size objects or with recursive sub-alists.
2646 @cindex deserializing
2649 Conversion from byte arrays to nested alists is also known as
2650 @dfn{deserializing} or @dfn{unpacking}, while going in the opposite
2651 direction is also known as @dfn{serializing} or @dfn{packing}.
2654 * Bindat Spec:: Describing data layout.
2655 * Bindat Functions:: Doing the unpacking and packing.
2656 * Bindat Examples:: Samples of what bindat.el can do for you!
2660 @subsection Describing Data Layout
2662 To control unpacking and packing, you write a @dfn{data layout
2663 specification}, a special nested list describing named and typed
2664 @dfn{fields}. This specification controls length of each field to be
2665 processed, and how to pack or unpack it. We normally keep bindat specs
2666 in variables whose names end in @samp{-bindat-spec}; that kind of name
2667 is automatically recognized as ``risky.''
2671 @cindex little endian
2672 @cindex network byte ordering
2673 A field's @dfn{type} describes the size (in bytes) of the object
2674 that the field represents and, in the case of multibyte fields, how
2675 the bytes are ordered within the field. The two possible orderings
2676 are ``big endian'' (also known as ``network byte ordering'') and
2677 ``little endian.'' For instance, the number @code{#x23cd} (decimal
2678 9165) in big endian would be the two bytes @code{#x23} @code{#xcd};
2679 and in little endian, @code{#xcd} @code{#x23}. Here are the possible
2685 Unsigned byte, with length 1.
2690 Unsigned integer in network byte order, with length 2.
2693 Unsigned integer in network byte order, with length 3.
2698 Unsigned integer in network byte order, with length 4.
2699 Note: These values may be limited by Emacs's integer implementation limits.
2704 Unsigned integer in little endian order, with length 2, 3 and 4, respectively.
2707 String of length @var{len}.
2709 @item strz @var{len}
2710 Zero-terminated string, in a fixed-size field with length @var{len}.
2712 @item vec @var{len} [@var{type}]
2713 Vector of @var{len} elements of type @var{type}, or bytes if not
2714 @var{type} is specified.
2715 The @var{type} is any of the simple types above, or another vector
2716 specified as a list @code{(vec @var{len} [@var{type}])}.
2719 Four-byte vector representing an Internet address. For example:
2720 @code{[127 0 0 1]} for localhost.
2722 @item bits @var{len}
2723 List of set bits in @var{len} bytes. The bytes are taken in big
2724 endian order and the bits are numbered starting with @code{8 *
2725 @var{len} @minus{} 1} and ending with zero. For example: @code{bits
2726 2} unpacks @code{#x28} @code{#x1c} to @code{(2 3 4 11 13)} and
2727 @code{#x1c} @code{#x28} to @code{(3 5 10 11 12)}.
2729 @item (eval @var{form})
2730 @var{form} is a Lisp expression evaluated at the moment the field is
2731 unpacked or packed. The result of the evaluation should be one of the
2732 above-listed type specifications.
2735 For a fixed-size field, the length @var{len} is given as an integer
2736 specifying the number of bytes in the field.
2738 When the length of a field is not fixed, it typically depends on the
2739 value of a preceding field. In this case, the length @var{len} can be
2740 given either as a list @code{(@var{name} ...)} identifying a
2741 @dfn{field name} in the format specified for @code{bindat-get-field}
2742 below, or by an expression @code{(eval @var{form})} where @var{form}
2743 should evaluate to an integer, specifying the field length.
2745 A field specification generally has the form @code{([@var{name}]
2746 @var{handler})}. The square braces indicate that @var{name} is
2747 optional. (Don't use names that are symbols meaningful as type
2748 specifications (above) or handler specifications (below), since that
2749 would be ambiguous.) @var{name} can be a symbol or the expression
2750 @code{(eval @var{form})}, in which case @var{form} should evaluate to
2753 @var{handler} describes how to unpack or pack the field and can be one
2758 Unpack/pack this field according to the type specification @var{type}.
2760 @item eval @var{form}
2761 Evaluate @var{form}, a Lisp expression, for side-effect only. If the
2762 field name is specified, the value is bound to that field name.
2764 @item fill @var{len}
2765 Skip @var{len} bytes. In packing, this leaves them unchanged,
2766 which normally means they remain zero. In unpacking, this means
2769 @item align @var{len}
2770 Skip to the next multiple of @var{len} bytes.
2772 @item struct @var{spec-name}
2773 Process @var{spec-name} as a sub-specification. This describes a
2774 structure nested within another structure.
2776 @item union @var{form} (@var{tag} @var{spec})@dots{}
2777 @c ??? I don't see how one would actually use this.
2778 @c ??? what kind of expression would be useful for @var{form}?
2779 Evaluate @var{form}, a Lisp expression, find the first @var{tag}
2780 that matches it, and process its associated data layout specification
2781 @var{spec}. Matching can occur in one of three ways:
2785 If a @var{tag} has the form @code{(eval @var{expr})}, evaluate
2786 @var{expr} with the variable @code{tag} dynamically bound to the value
2787 of @var{form}. A non-@code{nil} result indicates a match.
2790 @var{tag} matches if it is @code{equal} to the value of @var{form}.
2793 @var{tag} matches unconditionally if it is @code{t}.
2796 @item repeat @var{count} @var{field-specs}@dots{}
2797 Process the @var{field-specs} recursively, in order, then repeat
2798 starting from the first one, processing all the specs @var{count}
2799 times overall. The @var{count} is given using the same formats as a
2800 field length---if an @code{eval} form is used, it is evaluated just once.
2801 For correct operation, each spec in @var{field-specs} must include a name.
2804 For the @code{(eval @var{form})} forms used in a bindat specification,
2805 the @var{form} can access and update these dynamically bound variables
2810 Value of the last field processed.
2813 The data as a byte array.
2816 Current index (within @code{bindat-raw}) for unpacking or packing.
2819 The alist containing the structured data that have been unpacked so
2820 far, or the entire structure being packed. You can use
2821 @code{bindat-get-field} to access specific fields of this structure.
2825 Inside a @code{repeat} block, these contain the maximum number of
2826 repetitions (as specified by the @var{count} parameter), and the
2827 current repetition number (counting from 0). Setting @code{count} to
2828 zero will terminate the inner-most repeat block after the current
2829 repetition has completed.
2832 @node Bindat Functions
2833 @subsection Functions to Unpack and Pack Bytes
2835 In the following documentation, @var{spec} refers to a data layout
2836 specification, @code{bindat-raw} to a byte array, and @var{struct} to an
2837 alist representing unpacked field data.
2839 @defun bindat-unpack spec bindat-raw &optional bindat-idx
2840 This function unpacks data from the unibyte string or byte
2841 array @code{bindat-raw}
2842 according to @var{spec}. Normally this starts unpacking at the
2843 beginning of the byte array, but if @var{bindat-idx} is non-@code{nil}, it
2844 specifies a zero-based starting position to use instead.
2846 The value is an alist or nested alist in which each element describes
2850 @defun bindat-get-field struct &rest name
2851 This function selects a field's data from the nested alist
2852 @var{struct}. Usually @var{struct} was returned by
2853 @code{bindat-unpack}. If @var{name} corresponds to just one argument,
2854 that means to extract a top-level field value. Multiple @var{name}
2855 arguments specify repeated lookup of sub-structures. An integer name
2856 acts as an array index.
2858 For example, if @var{name} is @code{(a b 2 c)}, that means to find
2859 field @code{c} in the third element of subfield @code{b} of field
2860 @code{a}. (This corresponds to @code{struct.a.b[2].c} in C.)
2863 Although packing and unpacking operations change the organization of
2864 data (in memory), they preserve the data's @dfn{total length}, which is
2865 the sum of all the fields' lengths, in bytes. This value is not
2866 generally inherent in either the specification or alist alone; instead,
2867 both pieces of information contribute to its calculation. Likewise, the
2868 length of a string or array being unpacked may be longer than the data's
2869 total length as described by the specification.
2871 @defun bindat-length spec struct
2872 This function returns the total length of the data in @var{struct},
2873 according to @var{spec}.
2876 @defun bindat-pack spec struct &optional bindat-raw bindat-idx
2877 This function returns a byte array packed according to @var{spec} from
2878 the data in the alist @var{struct}. Normally it creates and fills a
2879 new byte array starting at the beginning. However, if @var{bindat-raw}
2880 is non-@code{nil}, it specifies a pre-allocated unibyte string or vector to
2881 pack into. If @var{bindat-idx} is non-@code{nil}, it specifies the starting
2882 offset for packing into @code{bindat-raw}.
2884 When pre-allocating, you should make sure @code{(length @var{bindat-raw})}
2885 meets or exceeds the total length to avoid an out-of-range error.
2888 @defun bindat-ip-to-string ip
2889 Convert the Internet address vector @var{ip} to a string in the usual
2893 (bindat-ip-to-string [127 0 0 1])
2894 @result{} "127.0.0.1"
2898 @node Bindat Examples
2899 @subsection Examples of Byte Unpacking and Packing
2901 Here is a complete example of byte unpacking and packing:
2904 (defvar fcookie-index-spec
2912 (:offset repeat (:count)
2914 "Description of a fortune cookie index file's contents.")
2916 (defun fcookie (cookies &optional index)
2917 "Display a random fortune cookie from file COOKIES.
2918 Optional second arg INDEX specifies the associated index
2919 filename, which is by default constructed by appending
2920 \".dat\" to COOKIES. Display cookie text in possibly
2921 new buffer \"*Fortune Cookie: BASENAME*\" where BASENAME
2922 is COOKIES without the directory part."
2923 (interactive "fCookies file: ")
2924 (let* ((info (with-temp-buffer
2925 (insert-file-contents-literally
2926 (or index (concat cookies ".dat")))
2927 (bindat-unpack fcookie-index-spec
2929 (sel (random (bindat-get-field info :count)))
2930 (beg (cdar (bindat-get-field info :offset sel)))
2931 (end (or (cdar (bindat-get-field info
2933 (nth 7 (file-attributes cookies)))))
2936 (format "*Fortune Cookie: %s*"
2937 (file-name-nondirectory cookies))))
2939 (insert-file-contents-literally
2940 cookies nil beg (- end 3))))
2942 (defun fcookie-create-index (cookies &optional index delim)
2943 "Scan file COOKIES, and write out its index file.
2944 Optional second arg INDEX specifies the index filename,
2945 which is by default constructed by appending \".dat\" to
2946 COOKIES. Optional third arg DELIM specifies the unibyte
2947 character which, when found on a line of its own in
2948 COOKIES, indicates the border between entries."
2949 (interactive "fCookies file: ")
2950 (setq delim (or delim ?%))
2951 (let ((delim-line (format "\n%c\n" delim))
2954 min p q len offsets)
2955 (unless (= 3 (string-bytes delim-line))
2956 (error "Delimiter cannot be represented in one byte"))
2958 (insert-file-contents-literally cookies)
2959 (while (and (setq p (point))
2960 (search-forward delim-line (point-max) t)
2961 (setq len (- (point) 3 p)))
2962 (setq count (1+ count)
2964 min (min (or min max) len)
2965 offsets (cons (1- p) offsets))))
2967 (set-buffer-multibyte nil)
2977 (:offset . ,(mapcar (lambda (o)
2978 (list (cons :foo o)))
2979 (nreverse offsets))))))
2980 (let ((coding-system-for-write 'raw-text-unix))
2981 (write-file (or index (concat cookies ".dat")))))))
2984 Following is an example of defining and unpacking a complex structure.
2985 Consider the following C structures:
2989 unsigned long dest_ip;
2990 unsigned long src_ip;
2991 unsigned short dest_port;
2992 unsigned short src_port;
2997 unsigned char opcode;
2998 unsigned short length; /* In network byte order */
2999 unsigned char id[8]; /* null-terminated string */
3000 unsigned char data[/* (length + 3) & ~3 */];
3004 struct header header;
3005 unsigned long counters[2]; /* In little endian order */
3006 unsigned char items;
3007 unsigned char filler[3];
3008 struct data item[/* items */];
3013 The corresponding data layout specification:
3025 (length u16) ;; network byte order
3031 '((header struct header-spec)
3032 (counters vec 2 u32r) ;; little endian order
3035 (item repeat (items)
3036 (struct data-spec))))
3039 A binary data representation:
3043 [ 192 168 1 100 192 168 1 101 01 28 21 32
3044 160 134 1 0 5 1 0 0 2 0 0 0
3045 2 3 0 5 ?A ?B ?C ?D ?E ?F 0 0 1 2 3 4 5 0 0 0
3046 1 4 0 7 ?B ?C ?D ?E ?F ?G 0 0 6 7 8 9 10 11 12 0 ])
3049 The corresponding decoded structure:
3052 (setq decoded (bindat-unpack packet-spec binary-data))
3055 (dest-ip . [192 168 1 100])
3056 (src-ip . [192 168 1 101])
3059 (counters . [100000 261])
3061 (item ((data . [1 2 3 4 5])
3066 ((data . [6 7 8 9 10 11 12])
3073 Fetching data from this structure:
3076 (bindat-get-field decoded 'item 1 'id)