2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2001,
4 @c 2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
5 @c See the file elisp.texi for copying conditions.
6 @setfilename ../../info/processes
7 @node Processes, Display, Abbrevs, Top
10 @cindex parent process
14 In the terminology of operating systems, a @dfn{process} is a space in
15 which a program can execute. Emacs runs in a process. Emacs Lisp
16 programs can invoke other programs in processes of their own. These are
17 called @dfn{subprocesses} or @dfn{child processes} of the Emacs process,
18 which is their @dfn{parent process}.
20 A subprocess of Emacs may be @dfn{synchronous} or @dfn{asynchronous},
21 depending on how it is created. When you create a synchronous
22 subprocess, the Lisp program waits for the subprocess to terminate
23 before continuing execution. When you create an asynchronous
24 subprocess, it can run in parallel with the Lisp program. This kind of
25 subprocess is represented within Emacs by a Lisp object which is also
26 called a ``process.'' Lisp programs can use this object to communicate
27 with the subprocess or to control it. For example, you can send
28 signals, obtain status information, receive output from the process, or
31 @defun processp object
32 This function returns @code{t} if @var{object} is a process,
37 * Subprocess Creation:: Functions that start subprocesses.
38 * Shell Arguments:: Quoting an argument to pass it to a shell.
39 * Synchronous Processes:: Details of using synchronous subprocesses.
40 * Asynchronous Processes:: Starting up an asynchronous subprocess.
41 * Deleting Processes:: Eliminating an asynchronous subprocess.
42 * Process Information:: Accessing run-status and other attributes.
43 * Input to Processes:: Sending input to an asynchronous subprocess.
44 * Signals to Processes:: Stopping, continuing or interrupting
45 an asynchronous subprocess.
46 * Output from Processes:: Collecting output from an asynchronous subprocess.
47 * Sentinels:: Sentinels run when process run-status changes.
48 * Query Before Exit:: Whether to query if exiting will kill a process.
49 * Transaction Queues:: Transaction-based communication with subprocesses.
50 * Network:: Opening network connections.
51 * Network Servers:: Network servers let Emacs accept net connections.
52 * Datagrams:: UDP network connections.
53 * Low-Level Network:: Lower-level but more general function
54 to create connections and servers.
55 * Misc Network:: Additional relevant functions for network connections.
56 * Byte Packing:: Using bindat to pack and unpack binary data.
59 @node Subprocess Creation
60 @section Functions that Create Subprocesses
62 There are three functions that create a new subprocess in which to run
63 a program. One of them, @code{start-process}, creates an asynchronous
64 process and returns a process object (@pxref{Asynchronous Processes}).
65 The other two, @code{call-process} and @code{call-process-region},
66 create a synchronous process and do not return a process object
67 (@pxref{Synchronous Processes}).
69 Synchronous and asynchronous processes are explained in the following
70 sections. Since the three functions are all called in a similar
71 fashion, their common arguments are described here.
73 @cindex execute program
74 @cindex @code{PATH} environment variable
75 @cindex @code{HOME} environment variable
76 In all cases, the function's @var{program} argument specifies the
77 program to be run. An error is signaled if the file is not found or
78 cannot be executed. If the file name is relative, the variable
79 @code{exec-path} contains a list of directories to search. Emacs
80 initializes @code{exec-path} when it starts up, based on the value of
81 the environment variable @code{PATH}. The standard file name
82 constructs, @samp{~}, @samp{.}, and @samp{..}, are interpreted as
83 usual in @code{exec-path}, but environment variable substitutions
84 (@samp{$HOME}, etc.) are not recognized; use
85 @code{substitute-in-file-name} to perform them (@pxref{File Name
86 Expansion}). @code{nil} in this list refers to
87 @code{default-directory}.
89 Executing a program can also try adding suffixes to the specified
93 This variable is a list of suffixes (strings) to try adding to the
94 specified program file name. The list should include @code{""} if you
95 want the name to be tried exactly as specified. The default value is
99 @strong{Please note:} The argument @var{program} contains only the
100 name of the program; it may not contain any command-line arguments. You
101 must use @var{args} to provide those.
103 Each of the subprocess-creating functions has a @var{buffer-or-name}
104 argument which specifies where the standard output from the program will
105 go. It should be a buffer or a buffer name; if it is a buffer name,
106 that will create the buffer if it does not already exist. It can also
107 be @code{nil}, which says to discard the output unless a filter function
108 handles it. (@xref{Filter Functions}, and @ref{Read and Print}.)
109 Normally, you should avoid having multiple processes send output to the
110 same buffer because their output would be intermixed randomly.
112 @cindex program arguments
113 All three of the subprocess-creating functions have a @code{&rest}
114 argument, @var{args}. The @var{args} must all be strings, and they are
115 supplied to @var{program} as separate command line arguments. Wildcard
116 characters and other shell constructs have no special meanings in these
117 strings, since the strings are passed directly to the specified program.
119 The subprocess gets its current directory from the value of
120 @code{default-directory} (@pxref{File Name Expansion}).
122 @cindex environment variables, subprocesses
123 The subprocess inherits its environment from Emacs, but you can
124 specify overrides for it with @code{process-environment}. @xref{System
127 @defvar exec-directory
129 The value of this variable is a string, the name of a directory that
130 contains programs that come with GNU Emacs, programs intended for Emacs
131 to invoke. The program @code{movemail} is an example of such a program;
132 Rmail uses it to fetch new mail from an inbox.
136 The value of this variable is a list of directories to search for
137 programs to run in subprocesses. Each element is either the name of a
138 directory (i.e., a string), or @code{nil}, which stands for the default
139 directory (which is the value of @code{default-directory}).
140 @cindex program directories
142 The value of @code{exec-path} is used by @code{call-process} and
143 @code{start-process} when the @var{program} argument is not an absolute
147 @node Shell Arguments
148 @section Shell Arguments
149 @cindex arguments for shell commands
150 @cindex shell command arguments
152 Lisp programs sometimes need to run a shell and give it a command
153 that contains file names that were specified by the user. These
154 programs ought to be able to support any valid file name. But the shell
155 gives special treatment to certain characters, and if these characters
156 occur in the file name, they will confuse the shell. To handle these
157 characters, use the function @code{shell-quote-argument}:
159 @defun shell-quote-argument argument
160 This function returns a string which represents, in shell syntax,
161 an argument whose actual contents are @var{argument}. It should
162 work reliably to concatenate the return value into a shell command
163 and then pass it to a shell for execution.
165 Precisely what this function does depends on your operating system. The
166 function is designed to work with the syntax of your system's standard
167 shell; if you use an unusual shell, you will need to redefine this
171 ;; @r{This example shows the behavior on GNU and Unix systems.}
172 (shell-quote-argument "foo > bar")
173 @result{} "foo\\ \\>\\ bar"
175 ;; @r{This example shows the behavior on MS-DOS and MS-Windows.}
176 (shell-quote-argument "foo > bar")
177 @result{} "\"foo > bar\""
180 Here's an example of using @code{shell-quote-argument} to construct
185 (shell-quote-argument oldfile)
187 (shell-quote-argument newfile))
191 @node Synchronous Processes
192 @section Creating a Synchronous Process
193 @cindex synchronous subprocess
195 After a @dfn{synchronous process} is created, Emacs waits for the
196 process to terminate before continuing. Starting Dired on GNU or
197 Unix@footnote{On other systems, Emacs uses a Lisp emulation of
198 @code{ls}; see @ref{Contents of Directories}.} is an example of this: it
199 runs @code{ls} in a synchronous process, then modifies the output
200 slightly. Because the process is synchronous, the entire directory
201 listing arrives in the buffer before Emacs tries to do anything with it.
203 While Emacs waits for the synchronous subprocess to terminate, the
204 user can quit by typing @kbd{C-g}. The first @kbd{C-g} tries to kill
205 the subprocess with a @code{SIGINT} signal; but it waits until the
206 subprocess actually terminates before quitting. If during that time the
207 user types another @kbd{C-g}, that kills the subprocess instantly with
208 @code{SIGKILL} and quits immediately (except on MS-DOS, where killing
209 other processes doesn't work). @xref{Quitting}.
211 The synchronous subprocess functions return an indication of how the
214 The output from a synchronous subprocess is generally decoded using a
215 coding system, much like text read from a file. The input sent to a
216 subprocess by @code{call-process-region} is encoded using a coding
217 system, much like text written into a file. @xref{Coding Systems}.
219 @defun call-process program &optional infile destination display &rest args
220 This function calls @var{program} in a separate process and waits for
223 The standard input for the process comes from file @var{infile} if
224 @var{infile} is not @code{nil}, and from the null device otherwise.
225 The argument @var{destination} says where to put the process output.
226 Here are the possibilities:
230 Insert the output in that buffer, before point. This includes both the
231 standard output stream and the standard error stream of the process.
234 Insert the output in a buffer with that name, before point.
237 Insert the output in the current buffer, before point.
243 Discard the output, and return @code{nil} immediately without waiting
244 for the subprocess to finish.
246 In this case, the process is not truly synchronous, since it can run in
247 parallel with Emacs; but you can think of it as synchronous in that
248 Emacs is essentially finished with the subprocess as soon as this
251 MS-DOS doesn't support asynchronous subprocesses, so this option doesn't
254 @item @code{(@var{real-destination} @var{error-destination})}
255 Keep the standard output stream separate from the standard error stream;
256 deal with the ordinary output as specified by @var{real-destination},
257 and dispose of the error output according to @var{error-destination}.
258 If @var{error-destination} is @code{nil}, that means to discard the
259 error output, @code{t} means mix it with the ordinary output, and a
260 string specifies a file name to redirect error output into.
262 You can't directly specify a buffer to put the error output in; that is
263 too difficult to implement. But you can achieve this result by sending
264 the error output to a temporary file and then inserting the file into a
268 If @var{display} is non-@code{nil}, then @code{call-process} redisplays
269 the buffer as output is inserted. (However, if the coding system chosen
270 for decoding output is @code{undecided}, meaning deduce the encoding
271 from the actual data, then redisplay sometimes cannot continue once
272 non-@acronym{ASCII} characters are encountered. There are fundamental
273 reasons why it is hard to fix this; see @ref{Output from Processes}.)
275 Otherwise the function @code{call-process} does no redisplay, and the
276 results become visible on the screen only when Emacs redisplays that
277 buffer in the normal course of events.
279 The remaining arguments, @var{args}, are strings that specify command
280 line arguments for the program.
282 The value returned by @code{call-process} (unless you told it not to
283 wait) indicates the reason for process termination. A number gives the
284 exit status of the subprocess; 0 means success, and any other value
285 means failure. If the process terminated with a signal,
286 @code{call-process} returns a string describing the signal.
288 In the examples below, the buffer @samp{foo} is current.
292 (call-process "pwd" nil t)
295 ---------- Buffer: foo ----------
296 /usr/user/lewis/manual
297 ---------- Buffer: foo ----------
301 (call-process "grep" nil "bar" nil "lewis" "/etc/passwd")
304 ---------- Buffer: bar ----------
305 lewis:5LTsHm66CSWKg:398:21:Bil Lewis:/user/lewis:/bin/csh
307 ---------- Buffer: bar ----------
311 Here is a good example of the use of @code{call-process}, which used to
312 be found in the definition of @code{insert-directory}:
316 (call-process insert-directory-program nil t nil @var{switches}
318 (concat (file-name-as-directory file) ".")
324 @defun process-file program &optional infile buffer display &rest args
325 This function processes files synchronously in a separate process. It
326 is similar to @code{call-process} but may invoke a file handler based
327 on the value of the variable @code{default-directory}. The current
328 working directory of the subprocess is @code{default-directory}.
330 The arguments are handled in almost the same way as for
331 @code{call-process}, with the following differences:
333 Some file handlers may not support all combinations and forms of the
334 arguments @var{infile}, @var{buffer}, and @var{display}. For example,
335 some file handlers might behave as if @var{display} were @code{nil},
336 regardless of the value actually passed. As another example, some
337 file handlers might not support separating standard output and error
338 output by way of the @var{buffer} argument.
340 If a file handler is invoked, it determines the program to run based
341 on the first argument @var{program}. For instance, consider that a
342 handler for remote files is invoked. Then the path that is used for
343 searching the program might be different than @code{exec-path}.
345 The second argument @var{infile} may invoke a file handler. The file
346 handler could be different from the handler chosen for the
347 @code{process-file} function itself. (For example,
348 @code{default-directory} could be on a remote host, whereas
349 @var{infile} is on another remote host. Or @code{default-directory}
350 could be non-special, whereas @var{infile} is on a remote host.)
352 If @var{buffer} is a list of the form @code{(@var{real-destination}
353 @var{error-destination})}, and @var{error-destination} names a file,
354 then the same remarks as for @var{infile} apply.
356 The remaining arguments (@var{args}) will be passed to the process
357 verbatim. Emacs is not involved in processing file names that are
358 present in @var{args}. To avoid confusion, it may be best to avoid
359 absolute file names in @var{args}, but rather to specify all file
360 names as relative to @code{default-directory}. The function
361 @code{file-relative-name} is useful for constructing such relative
365 @defun call-process-region start end program &optional delete destination display &rest args
366 This function sends the text from @var{start} to @var{end} as
367 standard input to a process running @var{program}. It deletes the text
368 sent if @var{delete} is non-@code{nil}; this is useful when
369 @var{destination} is @code{t}, to insert the output in the current
370 buffer in place of the input.
372 The arguments @var{destination} and @var{display} control what to do
373 with the output from the subprocess, and whether to update the display
374 as it comes in. For details, see the description of
375 @code{call-process}, above. If @var{destination} is the integer 0,
376 @code{call-process-region} discards the output and returns @code{nil}
377 immediately, without waiting for the subprocess to finish (this only
378 works if asynchronous subprocesses are supported).
380 The remaining arguments, @var{args}, are strings that specify command
381 line arguments for the program.
383 The return value of @code{call-process-region} is just like that of
384 @code{call-process}: @code{nil} if you told it to return without
385 waiting; otherwise, a number or string which indicates how the
386 subprocess terminated.
388 In the following example, we use @code{call-process-region} to run the
389 @code{cat} utility, with standard input being the first five characters
390 in buffer @samp{foo} (the word @samp{input}). @code{cat} copies its
391 standard input into its standard output. Since the argument
392 @var{destination} is @code{t}, this output is inserted in the current
397 ---------- Buffer: foo ----------
399 ---------- Buffer: foo ----------
403 (call-process-region 1 6 "cat" nil t)
406 ---------- Buffer: foo ----------
408 ---------- Buffer: foo ----------
412 The @code{shell-command-on-region} command uses
413 @code{call-process-region} like this:
419 shell-file-name ; @r{Name of program.}
420 nil ; @r{Do not delete region.}
421 buffer ; @r{Send output to @code{buffer}.}
422 nil ; @r{No redisplay during output.}
423 "-c" command) ; @r{Arguments for the shell.}
428 @defun call-process-shell-command command &optional infile destination display &rest args
429 This function executes the shell command @var{command} synchronously
430 in a separate process. The final arguments @var{args} are additional
431 arguments to add at the end of @var{command}. The other arguments
432 are handled as in @code{call-process}.
435 @defun process-file-shell-command command &optional infile destination display &rest args
436 This function is like @code{call-process-shell-command}, but uses
437 @code{process-file} internally. Depending on @code{default-directory},
438 @var{command} can be executed also on remote hosts.
441 @defun shell-command-to-string command
442 This function executes @var{command} (a string) as a shell command,
443 then returns the command's output as a string.
446 @node Asynchronous Processes
447 @section Creating an Asynchronous Process
448 @cindex asynchronous subprocess
450 After an @dfn{asynchronous process} is created, Emacs and the subprocess
451 both continue running immediately. The process thereafter runs
452 in parallel with Emacs, and the two can communicate with each other
453 using the functions described in the following sections. However,
454 communication is only partially asynchronous: Emacs sends data to the
455 process only when certain functions are called, and Emacs accepts data
456 from the process only when Emacs is waiting for input or for a time
459 Here we describe how to create an asynchronous process.
461 @defun start-process name buffer-or-name program &rest args
462 This function creates a new asynchronous subprocess and starts the
463 program @var{program} running in it. It returns a process object that
464 stands for the new subprocess in Lisp. The argument @var{name}
465 specifies the name for the process object; if a process with this name
466 already exists, then @var{name} is modified (by appending @samp{<1>},
467 etc.) to be unique. The buffer @var{buffer-or-name} is the buffer to
468 associate with the process.
470 The remaining arguments, @var{args}, are strings that specify command
471 line arguments for the program.
473 In the example below, the first process is started and runs (rather,
474 sleeps) for 100 seconds. Meanwhile, the second process is started, and
475 given the name @samp{my-process<1>} for the sake of uniqueness. It
476 inserts the directory listing at the end of the buffer @samp{foo},
477 before the first process finishes. Then it finishes, and a message to
478 that effect is inserted in the buffer. Much later, the first process
479 finishes, and another message is inserted in the buffer for it.
483 (start-process "my-process" "foo" "sleep" "100")
484 @result{} #<process my-process>
488 (start-process "my-process" "foo" "ls" "-l" "/user/lewis/bin")
489 @result{} #<process my-process<1>>
491 ---------- Buffer: foo ----------
493 lrwxrwxrwx 1 lewis 14 Jul 22 10:12 gnuemacs --> /emacs
494 -rwxrwxrwx 1 lewis 19 Jul 30 21:02 lemon
496 Process my-process<1> finished
498 Process my-process finished
499 ---------- Buffer: foo ----------
504 @defun start-file-process name buffer-or-name program &rest args
505 Like @code{start-process}, this function starts a new asynchronous
506 subprocess running @var{program} in it, and returns its process
507 object---when @code{default-directory} is not a magic file name.
509 If @code{default-directory} is magic, the function invokes its file
510 handler instead. This handler ought to run @var{program}, perhaps on
511 the local host, perhaps on a remote host that corresponds to
512 @code{default-directory}. In the latter case, the local part of
513 @code{default-directory} becomes the working directory of the process.
515 This function does not try to invoke file name handlers for
516 @var{program} or for the @var{program-args}.
518 Depending on the implementation of the file handler, it might not be
519 possible to apply @code{process-filter} or @code{process-sentinel} to
520 the resulting process object (@pxref{Filter Functions}, @pxref{Sentinels}).
522 Some file handlers may not support @code{start-file-process} (for
523 example @code{ange-ftp-hook-function}). In such cases, the function
524 does nothing and returns @code{nil}.
527 @defun start-process-shell-command name buffer-or-name command &rest command-args
528 This function is like @code{start-process} except that it uses a shell
529 to execute the specified command. The argument @var{command} is a shell
530 command name, and @var{command-args} are the arguments for the shell
531 command. The variable @code{shell-file-name} specifies which shell to
534 The point of running a program through the shell, rather than directly
535 with @code{start-process}, is so that you can employ shell features such
536 as wildcards in the arguments. It follows that if you include an
537 arbitrary user-specified arguments in the command, you should quote it
538 with @code{shell-quote-argument} first, so that any special shell
539 characters do @emph{not} have their special shell meanings. @xref{Shell
543 @defun start-file-process-shell-command name buffer-or-name command &rest command-args
544 This function is like @code{start-process-shell-command}, but uses
545 @code{start-file-process} internally. By this, @var{command} can be
546 executed also on remote hosts, depending on @code{default-directory}.
549 @defvar process-connection-type
551 @cindex @acronym{PTY}s
552 This variable controls the type of device used to communicate with
553 asynchronous subprocesses. If it is non-@code{nil}, then @acronym{PTY}s are
554 used, when available. Otherwise, pipes are used.
556 @acronym{PTY}s are usually preferable for processes visible to the user, as
557 in Shell mode, because they allow job control (@kbd{C-c}, @kbd{C-z},
558 etc.) to work between the process and its children, whereas pipes do
559 not. For subprocesses used for internal purposes by programs, it is
560 often better to use a pipe, because they are more efficient. In
561 addition, the total number of @acronym{PTY}s is limited on many systems and
562 it is good not to waste them.
564 The value of @code{process-connection-type} takes effect when
565 @code{start-process} is called. So you can specify how to communicate
566 with one subprocess by binding the variable around the call to
567 @code{start-process}.
571 (let ((process-connection-type nil)) ; @r{Use a pipe.}
572 (start-process @dots{}))
576 To determine whether a given subprocess actually got a pipe or a
577 @acronym{PTY}, use the function @code{process-tty-name} (@pxref{Process
581 @node Deleting Processes
582 @section Deleting Processes
583 @cindex deleting processes
585 @dfn{Deleting a process} disconnects Emacs immediately from the
586 subprocess. Processes are deleted automatically after they terminate,
587 but not necessarily right away. You can delete a process explicitly
588 at any time. If you delete a terminated process explicitly before it
589 is deleted automatically, no harm results. Deleting a running
590 process sends a signal to terminate it (and its child processes if
591 any), and calls the process sentinel if it has one. @xref{Sentinels}.
593 When a process is deleted, the process object itself continues to
594 exist as long as other Lisp objects point to it. All the Lisp
595 primitives that work on process objects accept deleted processes, but
596 those that do I/O or send signals will report an error. The process
597 mark continues to point to the same place as before, usually into a
598 buffer where output from the process was being inserted.
600 @defopt delete-exited-processes
601 This variable controls automatic deletion of processes that have
602 terminated (due to calling @code{exit} or to a signal). If it is
603 @code{nil}, then they continue to exist until the user runs
604 @code{list-processes}. Otherwise, they are deleted immediately after
608 @defun delete-process process
609 This function deletes a process, killing it with a @code{SIGKILL}
610 signal. The argument may be a process, the name of a process, a
611 buffer, or the name of a buffer. (A buffer or buffer-name stands for
612 the process that @code{get-buffer-process} returns.) Calling
613 @code{delete-process} on a running process terminates it, updates the
614 process status, and runs the sentinel (if any) immediately. If the
615 process has already terminated, calling @code{delete-process} has no
616 effect on its status, or on the running of its sentinel (which will
617 happen sooner or later).
621 (delete-process "*shell*")
627 @node Process Information
628 @section Process Information
630 Several functions return information about processes.
631 @code{list-processes} is provided for interactive use.
633 @deffn Command list-processes &optional query-only
634 This command displays a listing of all living processes. In addition,
635 it finally deletes any process whose status was @samp{Exited} or
636 @samp{Signaled}. It returns @code{nil}.
638 If @var{query-only} is non-@code{nil} then it lists only processes
639 whose query flag is non-@code{nil}. @xref{Query Before Exit}.
643 This function returns a list of all processes that have not been deleted.
648 @result{} (#<process display-time> #<process shell>)
653 @defun get-process name
654 This function returns the process named @var{name}, or @code{nil} if
655 there is none. An error is signaled if @var{name} is not a string.
659 (get-process "shell")
660 @result{} #<process shell>
665 @defun process-command process
666 This function returns the command that was executed to start
667 @var{process}. This is a list of strings, the first string being the
668 program executed and the rest of the strings being the arguments that
669 were given to the program.
673 (process-command (get-process "shell"))
674 @result{} ("/bin/csh" "-i")
679 @defun process-id process
680 This function returns the @acronym{PID} of @var{process}. This is an
681 integer that distinguishes the process @var{process} from all other
682 processes running on the same computer at the current time. The
683 @acronym{PID} of a process is chosen by the operating system kernel when the
684 process is started and remains constant as long as the process exists.
687 @defun process-name process
688 This function returns the name of @var{process}.
691 @defun process-status process-name
692 This function returns the status of @var{process-name} as a symbol.
693 The argument @var{process-name} must be a process, a buffer, a
694 process name (string) or a buffer name (string).
696 The possible values for an actual subprocess are:
700 for a process that is running.
702 for a process that is stopped but continuable.
704 for a process that has exited.
706 for a process that has received a fatal signal.
708 for a network connection that is open.
710 for a network connection that is closed. Once a connection
711 is closed, you cannot reopen it, though you might be able to open
712 a new connection to the same place.
714 for a non-blocking connection that is waiting to complete.
716 for a non-blocking connection that has failed to complete.
718 for a network server that is listening.
720 if @var{process-name} is not the name of an existing process.
725 (process-status "shell")
729 (process-status (get-buffer "*shell*"))
734 @result{} #<process xx<1>>
740 For a network connection, @code{process-status} returns one of the symbols
741 @code{open} or @code{closed}. The latter means that the other side
742 closed the connection, or Emacs did @code{delete-process}.
745 @defun process-exit-status process
746 This function returns the exit status of @var{process} or the signal
747 number that killed it. (Use the result of @code{process-status} to
748 determine which of those it is.) If @var{process} has not yet
749 terminated, the value is 0.
752 @defun process-tty-name process
753 This function returns the terminal name that @var{process} is using for
754 its communication with Emacs---or @code{nil} if it is using pipes
755 instead of a terminal (see @code{process-connection-type} in
756 @ref{Asynchronous Processes}).
759 @defun process-coding-system process
760 @anchor{Coding systems for a subprocess}
761 This function returns a cons cell describing the coding systems in use
762 for decoding output from @var{process} and for encoding input to
763 @var{process} (@pxref{Coding Systems}). The value has this form:
766 (@var{coding-system-for-decoding} . @var{coding-system-for-encoding})
770 @defun set-process-coding-system process &optional decoding-system encoding-system
771 This function specifies the coding systems to use for subsequent output
772 from and input to @var{process}. It will use @var{decoding-system} to
773 decode subprocess output, and @var{encoding-system} to encode subprocess
777 Every process also has a property list that you can use to store
778 miscellaneous values associated with the process.
780 @defun process-get process propname
781 This function returns the value of the @var{propname} property
785 @defun process-put process propname value
786 This function sets the value of the @var{propname} property
787 of @var{process} to @var{value}.
790 @defun process-plist process
791 This function returns the process plist of @var{process}.
794 @defun set-process-plist process plist
795 This function sets the process plist of @var{process} to @var{plist}.
798 @node Input to Processes
799 @section Sending Input to Processes
800 @cindex process input
802 Asynchronous subprocesses receive input when it is sent to them by
803 Emacs, which is done with the functions in this section. You must
804 specify the process to send input to, and the input data to send. The
805 data appears on the ``standard input'' of the subprocess.
807 Some operating systems have limited space for buffered input in a
808 @acronym{PTY}. On these systems, Emacs sends an @acronym{EOF}
809 periodically amidst the other characters, to force them through. For
810 most programs, these @acronym{EOF}s do no harm.
812 Subprocess input is normally encoded using a coding system before the
813 subprocess receives it, much like text written into a file. You can use
814 @code{set-process-coding-system} to specify which coding system to use
815 (@pxref{Process Information}). Otherwise, the coding system comes from
816 @code{coding-system-for-write}, if that is non-@code{nil}; or else from
817 the defaulting mechanism (@pxref{Default Coding Systems}).
819 Sometimes the system is unable to accept input for that process,
820 because the input buffer is full. When this happens, the send functions
821 wait a short while, accepting output from subprocesses, and then try
822 again. This gives the subprocess a chance to read more of its pending
823 input and make space in the buffer. It also allows filters, sentinels
824 and timers to run---so take account of that in writing your code.
826 In these functions, the @var{process} argument can be a process or
827 the name of a process, or a buffer or buffer name (which stands
828 for a process via @code{get-buffer-process}). @code{nil} means
829 the current buffer's process.
831 @defun process-send-string process string
832 This function sends @var{process} the contents of @var{string} as
833 standard input. If it is @code{nil}, the current buffer's process is used.
835 The function returns @code{nil}.
839 (process-send-string "shell<1>" "ls\n")
845 ---------- Buffer: *shell* ----------
847 introduction.texi syntax-tables.texi~
848 introduction.texi~ text.texi
849 introduction.txt text.texi~
851 ---------- Buffer: *shell* ----------
856 @defun process-send-region process start end
857 This function sends the text in the region defined by @var{start} and
858 @var{end} as standard input to @var{process}.
860 An error is signaled unless both @var{start} and @var{end} are
861 integers or markers that indicate positions in the current buffer. (It
862 is unimportant which number is larger.)
865 @defun process-send-eof &optional process
866 This function makes @var{process} see an end-of-file in its
867 input. The @acronym{EOF} comes after any text already sent to it.
869 The function returns @var{process}.
873 (process-send-eof "shell")
879 @defun process-running-child-p process
880 This function will tell you whether a subprocess has given control of
881 its terminal to its own child process. The value is @code{t} if this is
882 true, or if Emacs cannot tell; it is @code{nil} if Emacs can be certain
886 @node Signals to Processes
887 @section Sending Signals to Processes
888 @cindex process signals
889 @cindex sending signals
892 @dfn{Sending a signal} to a subprocess is a way of interrupting its
893 activities. There are several different signals, each with its own
894 meaning. The set of signals and their names is defined by the operating
895 system. For example, the signal @code{SIGINT} means that the user has
896 typed @kbd{C-c}, or that some analogous thing has happened.
898 Each signal has a standard effect on the subprocess. Most signals
899 kill the subprocess, but some stop or resume execution instead. Most
900 signals can optionally be handled by programs; if the program handles
901 the signal, then we can say nothing in general about its effects.
903 You can send signals explicitly by calling the functions in this
904 section. Emacs also sends signals automatically at certain times:
905 killing a buffer sends a @code{SIGHUP} signal to all its associated
906 processes; killing Emacs sends a @code{SIGHUP} signal to all remaining
907 processes. (@code{SIGHUP} is a signal that usually indicates that the
908 user hung up the phone.)
910 Each of the signal-sending functions takes two optional arguments:
911 @var{process} and @var{current-group}.
913 The argument @var{process} must be either a process, a process
914 name, a buffer, a buffer name, or @code{nil}. A buffer or buffer name
915 stands for a process through @code{get-buffer-process}. @code{nil}
916 stands for the process associated with the current buffer. An error
917 is signaled if @var{process} does not identify a process.
919 The argument @var{current-group} is a flag that makes a difference
920 when you are running a job-control shell as an Emacs subprocess. If it
921 is non-@code{nil}, then the signal is sent to the current process-group
922 of the terminal that Emacs uses to communicate with the subprocess. If
923 the process is a job-control shell, this means the shell's current
924 subjob. If it is @code{nil}, the signal is sent to the process group of
925 the immediate subprocess of Emacs. If the subprocess is a job-control
926 shell, this is the shell itself.
928 The flag @var{current-group} has no effect when a pipe is used to
929 communicate with the subprocess, because the operating system does not
930 support the distinction in the case of pipes. For the same reason,
931 job-control shells won't work when a pipe is used. See
932 @code{process-connection-type} in @ref{Asynchronous Processes}.
934 @defun interrupt-process &optional process current-group
935 This function interrupts the process @var{process} by sending the
936 signal @code{SIGINT}. Outside of Emacs, typing the ``interrupt
937 character'' (normally @kbd{C-c} on some systems, and @code{DEL} on
938 others) sends this signal. When the argument @var{current-group} is
939 non-@code{nil}, you can think of this function as ``typing @kbd{C-c}''
940 on the terminal by which Emacs talks to the subprocess.
943 @defun kill-process &optional process current-group
944 This function kills the process @var{process} by sending the
945 signal @code{SIGKILL}. This signal kills the subprocess immediately,
946 and cannot be handled by the subprocess.
949 @defun quit-process &optional process current-group
950 This function sends the signal @code{SIGQUIT} to the process
951 @var{process}. This signal is the one sent by the ``quit
952 character'' (usually @kbd{C-b} or @kbd{C-\}) when you are not inside
956 @defun stop-process &optional process current-group
957 This function stops the process @var{process} by sending the
958 signal @code{SIGTSTP}. Use @code{continue-process} to resume its
961 Outside of Emacs, on systems with job control, the ``stop character''
962 (usually @kbd{C-z}) normally sends this signal. When
963 @var{current-group} is non-@code{nil}, you can think of this function as
964 ``typing @kbd{C-z}'' on the terminal Emacs uses to communicate with the
968 @defun continue-process &optional process current-group
969 This function resumes execution of the process @var{process} by sending
970 it the signal @code{SIGCONT}. This presumes that @var{process} was
975 @defun signal-process process signal
976 This function sends a signal to process @var{process}. The argument
977 @var{signal} specifies which signal to send; it should be an integer.
979 The @var{process} argument can be a system process @acronym{ID}; that
980 allows you to send signals to processes that are not children of
984 @node Output from Processes
985 @section Receiving Output from Processes
986 @cindex process output
987 @cindex output from processes
989 There are two ways to receive the output that a subprocess writes to
990 its standard output stream. The output can be inserted in a buffer,
991 which is called the associated buffer of the process, or a function
992 called the @dfn{filter function} can be called to act on the output. If
993 the process has no buffer and no filter function, its output is
996 When a subprocess terminates, Emacs reads any pending output,
997 then stops reading output from that subprocess. Therefore, if the
998 subprocess has children that are still live and still producing
999 output, Emacs won't receive that output.
1001 Output from a subprocess can arrive only while Emacs is waiting: when
1002 reading terminal input, in @code{sit-for} and @code{sleep-for}
1003 (@pxref{Waiting}), and in @code{accept-process-output} (@pxref{Accepting
1004 Output}). This minimizes the problem of timing errors that usually
1005 plague parallel programming. For example, you can safely create a
1006 process and only then specify its buffer or filter function; no output
1007 can arrive before you finish, if the code in between does not call any
1008 primitive that waits.
1010 @defvar process-adaptive-read-buffering
1011 On some systems, when Emacs reads the output from a subprocess, the
1012 output data is read in very small blocks, potentially resulting in
1013 very poor performance. This behavior can be remedied to some extent
1014 by setting the variable @var{process-adaptive-read-buffering} to a
1015 non-@code{nil} value (the default), as it will automatically delay reading
1016 from such processes, thus allowing them to produce more output before
1017 Emacs tries to read it.
1020 It is impossible to separate the standard output and standard error
1021 streams of the subprocess, because Emacs normally spawns the subprocess
1022 inside a pseudo-TTY, and a pseudo-TTY has only one output channel. If
1023 you want to keep the output to those streams separate, you should
1024 redirect one of them to a file---for example, by using an appropriate
1028 * Process Buffers:: If no filter, output is put in a buffer.
1029 * Filter Functions:: Filter functions accept output from the process.
1030 * Decoding Output:: Filters can get unibyte or multibyte strings.
1031 * Accepting Output:: How to wait until process output arrives.
1034 @node Process Buffers
1035 @subsection Process Buffers
1037 A process can (and usually does) have an @dfn{associated buffer},
1038 which is an ordinary Emacs buffer that is used for two purposes: storing
1039 the output from the process, and deciding when to kill the process. You
1040 can also use the buffer to identify a process to operate on, since in
1041 normal practice only one process is associated with any given buffer.
1042 Many applications of processes also use the buffer for editing input to
1043 be sent to the process, but this is not built into Emacs Lisp.
1045 Unless the process has a filter function (@pxref{Filter Functions}),
1046 its output is inserted in the associated buffer. The position to insert
1047 the output is determined by the @code{process-mark}, which is then
1048 updated to point to the end of the text just inserted. Usually, but not
1049 always, the @code{process-mark} is at the end of the buffer.
1051 @defun process-buffer process
1052 This function returns the associated buffer of the process
1057 (process-buffer (get-process "shell"))
1058 @result{} #<buffer *shell*>
1063 @defun process-mark process
1064 This function returns the process marker for @var{process}, which is the
1065 marker that says where to insert output from the process.
1067 If @var{process} does not have a buffer, @code{process-mark} returns a
1068 marker that points nowhere.
1070 Insertion of process output in a buffer uses this marker to decide where
1071 to insert, and updates it to point after the inserted text. That is why
1072 successive batches of output are inserted consecutively.
1074 Filter functions normally should use this marker in the same fashion
1075 as is done by direct insertion of output in the buffer. A good
1076 example of a filter function that uses @code{process-mark} is found at
1077 the end of the following section.
1079 When the user is expected to enter input in the process buffer for
1080 transmission to the process, the process marker separates the new input
1081 from previous output.
1084 @defun set-process-buffer process buffer
1085 This function sets the buffer associated with @var{process} to
1086 @var{buffer}. If @var{buffer} is @code{nil}, the process becomes
1087 associated with no buffer.
1090 @defun get-buffer-process buffer-or-name
1091 This function returns a nondeleted process associated with the buffer
1092 specified by @var{buffer-or-name}. If there are several processes
1093 associated with it, this function chooses one (currently, the one most
1094 recently created, but don't count on that). Deletion of a process
1095 (see @code{delete-process}) makes it ineligible for this function to
1098 It is usually a bad idea to have more than one process associated with
1103 (get-buffer-process "*shell*")
1104 @result{} #<process shell>
1108 Killing the process's buffer deletes the process, which kills the
1109 subprocess with a @code{SIGHUP} signal (@pxref{Signals to Processes}).
1112 @node Filter Functions
1113 @subsection Process Filter Functions
1114 @cindex filter function
1115 @cindex process filter
1117 A process @dfn{filter function} is a function that receives the
1118 standard output from the associated process. If a process has a filter,
1119 then @emph{all} output from that process is passed to the filter. The
1120 process buffer is used directly for output from the process only when
1123 The filter function can only be called when Emacs is waiting for
1124 something, because process output arrives only at such times. Emacs
1125 waits when reading terminal input, in @code{sit-for} and
1126 @code{sleep-for} (@pxref{Waiting}), and in @code{accept-process-output}
1127 (@pxref{Accepting Output}).
1129 A filter function must accept two arguments: the associated process
1130 and a string, which is output just received from it. The function is
1131 then free to do whatever it chooses with the output.
1133 Quitting is normally inhibited within a filter function---otherwise,
1134 the effect of typing @kbd{C-g} at command level or to quit a user
1135 command would be unpredictable. If you want to permit quitting inside
1136 a filter function, bind @code{inhibit-quit} to @code{nil}. In most
1137 cases, the right way to do this is with the macro
1138 @code{with-local-quit}. @xref{Quitting}.
1140 If an error happens during execution of a filter function, it is
1141 caught automatically, so that it doesn't stop the execution of whatever
1142 program was running when the filter function was started. However, if
1143 @code{debug-on-error} is non-@code{nil}, the error-catching is turned
1144 off. This makes it possible to use the Lisp debugger to debug the
1145 filter function. @xref{Debugger}.
1147 Many filter functions sometimes or always insert the text in the
1148 process's buffer, mimicking the actions of Emacs when there is no
1149 filter. Such filter functions need to use @code{set-buffer} in order to
1150 be sure to insert in that buffer. To avoid setting the current buffer
1151 semipermanently, these filter functions must save and restore the
1152 current buffer. They should also update the process marker, and in some
1153 cases update the value of point. Here is how to do these things:
1157 (defun ordinary-insertion-filter (proc string)
1158 (with-current-buffer (process-buffer proc)
1159 (let ((moving (= (point) (process-mark proc))))
1163 ;; @r{Insert the text, advancing the process marker.}
1164 (goto-char (process-mark proc))
1166 (set-marker (process-mark proc) (point)))
1167 (if moving (goto-char (process-mark proc))))))
1172 The reason to use @code{with-current-buffer}, rather than using
1173 @code{save-excursion} to save and restore the current buffer, is so as
1174 to preserve the change in point made by the second call to
1177 To make the filter force the process buffer to be visible whenever new
1178 text arrives, insert the following line just before the
1179 @code{with-current-buffer} construct:
1182 (display-buffer (process-buffer proc))
1185 To force point to the end of the new output, no matter where it was
1186 previously, eliminate the variable @code{moving} and call
1187 @code{goto-char} unconditionally.
1189 In earlier Emacs versions, every filter function that did regular
1190 expression searching or matching had to explicitly save and restore the
1191 match data. Now Emacs does this automatically for filter functions;
1192 they never need to do it explicitly. @xref{Match Data}.
1194 A filter function that writes the output into the buffer of the
1195 process should check whether the buffer is still alive. If it tries to
1196 insert into a dead buffer, it will get an error. The expression
1197 @code{(buffer-name (process-buffer @var{process}))} returns @code{nil}
1198 if the buffer is dead.
1200 The output to the function may come in chunks of any size. A program
1201 that produces the same output twice in a row may send it as one batch of
1202 200 characters one time, and five batches of 40 characters the next. If
1203 the filter looks for certain text strings in the subprocess output, make
1204 sure to handle the case where one of these strings is split across two
1205 or more batches of output.
1207 @defun set-process-filter process filter
1208 This function gives @var{process} the filter function @var{filter}. If
1209 @var{filter} is @code{nil}, it gives the process no filter.
1212 @defun process-filter process
1213 This function returns the filter function of @var{process}, or @code{nil}
1217 Here is an example of use of a filter function:
1221 (defun keep-output (process output)
1222 (setq kept (cons output kept)))
1223 @result{} keep-output
1230 (set-process-filter (get-process "shell") 'keep-output)
1231 @result{} keep-output
1234 (process-send-string "shell" "ls ~/other\n")
1237 @result{} ("lewis@@slug[8] % "
1240 "FINAL-W87-SHORT.MSS backup.otl kolstad.mss~
1241 address.txt backup.psf kolstad.psf
1242 backup.bib~ david.mss resume-Dec-86.mss~
1243 backup.err david.psf resume-Dec.psf
1244 backup.mss dland syllabus.mss
1246 "#backups.mss# backup.mss~ kolstad.mss
1251 @ignore @c The code in this example doesn't show the right way to do things.
1252 Here is another, more realistic example, which demonstrates how to use
1253 the process mark to do insertion in the same fashion as is done when
1254 there is no filter function:
1258 ;; @r{Insert input in the buffer specified by @code{my-shell-buffer}}
1259 ;; @r{and make sure that buffer is shown in some window.}
1260 (defun my-process-filter (proc str)
1261 (let ((cur (selected-window))
1263 (pop-to-buffer my-shell-buffer)
1266 (goto-char (point-max))
1268 (set-marker (process-mark proc) (point-max))
1269 (select-window cur)))
1274 @node Decoding Output
1275 @subsection Decoding Process Output
1276 @cindex decode process output
1278 When Emacs writes process output directly into a multibyte buffer,
1279 it decodes the output according to the process output coding system.
1280 If the coding system is @code{raw-text} or @code{no-conversion}, Emacs
1281 converts the unibyte output to multibyte using
1282 @code{string-to-multibyte}, and inserts the resulting multibyte text.
1284 You can use @code{set-process-coding-system} to specify which coding
1285 system to use (@pxref{Process Information}). Otherwise, the coding
1286 system comes from @code{coding-system-for-read}, if that is
1287 non-@code{nil}; or else from the defaulting mechanism (@pxref{Default
1290 @strong{Warning:} Coding systems such as @code{undecided} which
1291 determine the coding system from the data do not work entirely
1292 reliably with asynchronous subprocess output. This is because Emacs
1293 has to process asynchronous subprocess output in batches, as it
1294 arrives. Emacs must try to detect the proper coding system from one
1295 batch at a time, and this does not always work. Therefore, if at all
1296 possible, specify a coding system that determines both the character
1297 code conversion and the end of line conversion---that is, one like
1298 @code{latin-1-unix}, rather than @code{undecided} or @code{latin-1}.
1300 @c Let's keep the index entries that were there for
1301 @c set-process-filter-multibyte and process-filter-multibyte-p,
1302 @cindex filter multibyte flag, of process
1303 @cindex process filter multibyte flag
1304 When Emacs calls a process filter function, it provides the process
1305 output as a multibyte string or as a unibyte string according to the
1306 process's filter coding system. Emacs
1307 decodes the output according to the process output coding system,
1308 which usually produces a multibyte string, except for coding systems
1309 such as @code{binary} and @code{raw-text}
1311 @node Accepting Output
1312 @subsection Accepting Output from Processes
1313 @cindex accept input from processes
1315 Output from asynchronous subprocesses normally arrives only while
1316 Emacs is waiting for some sort of external event, such as elapsed time
1317 or terminal input. Occasionally it is useful in a Lisp program to
1318 explicitly permit output to arrive at a specific point, or even to wait
1319 until output arrives from a process.
1321 @defun accept-process-output &optional process seconds millisec just-this-one
1322 This function allows Emacs to read pending output from processes. The
1323 output is inserted in the associated buffers or given to their filter
1324 functions. If @var{process} is non-@code{nil} then this function does
1325 not return until some output has been received from @var{process}.
1328 The arguments @var{seconds} and @var{millisec} let you specify timeout
1329 periods. The former specifies a period measured in seconds and the
1330 latter specifies one measured in milliseconds. The two time periods
1331 thus specified are added together, and @code{accept-process-output}
1332 returns after that much time, whether or not there has been any
1335 The argument @var{millisec} is semi-obsolete nowadays because
1336 @var{seconds} can be a floating point number to specify waiting a
1337 fractional number of seconds. If @var{seconds} is 0, the function
1338 accepts whatever output is pending but does not wait.
1340 @c Emacs 22.1 feature
1341 If @var{process} is a process, and the argument @var{just-this-one} is
1342 non-@code{nil}, only output from that process is handled, suspending output
1343 from other processes until some output has been received from that
1344 process or the timeout expires. If @var{just-this-one} is an integer,
1345 also inhibit running timers. This feature is generally not
1346 recommended, but may be necessary for specific applications, such as
1349 The function @code{accept-process-output} returns non-@code{nil} if it
1350 did get some output, or @code{nil} if the timeout expired before output
1355 @section Sentinels: Detecting Process Status Changes
1356 @cindex process sentinel
1357 @cindex sentinel (of process)
1359 A @dfn{process sentinel} is a function that is called whenever the
1360 associated process changes status for any reason, including signals
1361 (whether sent by Emacs or caused by the process's own actions) that
1362 terminate, stop, or continue the process. The process sentinel is
1363 also called if the process exits. The sentinel receives two
1364 arguments: the process for which the event occurred, and a string
1365 describing the type of event.
1367 The string describing the event looks like one of the following:
1371 @code{"finished\n"}.
1374 @code{"exited abnormally with code @var{exitcode}\n"}.
1377 @code{"@var{name-of-signal}\n"}.
1380 @code{"@var{name-of-signal} (core dumped)\n"}.
1383 A sentinel runs only while Emacs is waiting (e.g., for terminal
1384 input, or for time to elapse, or for process output). This avoids the
1385 timing errors that could result from running them at random places in
1386 the middle of other Lisp programs. A program can wait, so that
1387 sentinels will run, by calling @code{sit-for} or @code{sleep-for}
1388 (@pxref{Waiting}), or @code{accept-process-output} (@pxref{Accepting
1389 Output}). Emacs also allows sentinels to run when the command loop is
1390 reading input. @code{delete-process} calls the sentinel when it
1391 terminates a running process.
1393 Emacs does not keep a queue of multiple reasons to call the sentinel
1394 of one process; it records just the current status and the fact that
1395 there has been a change. Therefore two changes in status, coming in
1396 quick succession, can call the sentinel just once. However, process
1397 termination will always run the sentinel exactly once. This is
1398 because the process status can't change again after termination.
1400 Emacs explicitly checks for output from the process before running
1401 the process sentinel. Once the sentinel runs due to process
1402 termination, no further output can arrive from the process.
1404 A sentinel that writes the output into the buffer of the process
1405 should check whether the buffer is still alive. If it tries to insert
1406 into a dead buffer, it will get an error. If the buffer is dead,
1407 @code{(buffer-name (process-buffer @var{process}))} returns @code{nil}.
1409 Quitting is normally inhibited within a sentinel---otherwise, the
1410 effect of typing @kbd{C-g} at command level or to quit a user command
1411 would be unpredictable. If you want to permit quitting inside a
1412 sentinel, bind @code{inhibit-quit} to @code{nil}. In most cases, the
1413 right way to do this is with the macro @code{with-local-quit}.
1416 If an error happens during execution of a sentinel, it is caught
1417 automatically, so that it doesn't stop the execution of whatever
1418 programs was running when the sentinel was started. However, if
1419 @code{debug-on-error} is non-@code{nil}, the error-catching is turned
1420 off. This makes it possible to use the Lisp debugger to debug the
1421 sentinel. @xref{Debugger}.
1423 While a sentinel is running, the process sentinel is temporarily
1424 set to @code{nil} so that the sentinel won't run recursively.
1425 For this reason it is not possible for a sentinel to specify
1428 In earlier Emacs versions, every sentinel that did regular expression
1429 searching or matching had to explicitly save and restore the match data.
1430 Now Emacs does this automatically for sentinels; they never need to do
1431 it explicitly. @xref{Match Data}.
1433 @defun set-process-sentinel process sentinel
1434 This function associates @var{sentinel} with @var{process}. If
1435 @var{sentinel} is @code{nil}, then the process will have no sentinel.
1436 The default behavior when there is no sentinel is to insert a message in
1437 the process's buffer when the process status changes.
1439 Changes in process sentinel take effect immediately---if the sentinel
1440 is slated to be run but has not been called yet, and you specify a new
1441 sentinel, the eventual call to the sentinel will use the new one.
1445 (defun msg-me (process event)
1447 (format "Process: %s had the event `%s'" process event)))
1448 (set-process-sentinel (get-process "shell") 'msg-me)
1452 (kill-process (get-process "shell"))
1453 @print{} Process: #<process shell> had the event `killed'
1454 @result{} #<process shell>
1459 @defun process-sentinel process
1460 This function returns the sentinel of @var{process}, or @code{nil} if it
1464 @defun waiting-for-user-input-p
1465 While a sentinel or filter function is running, this function returns
1466 non-@code{nil} if Emacs was waiting for keyboard input from the user at
1467 the time the sentinel or filter function was called, @code{nil} if it
1471 @node Query Before Exit
1472 @section Querying Before Exit
1474 When Emacs exits, it terminates all its subprocesses by sending them
1475 the @code{SIGHUP} signal. Because subprocesses may be doing
1476 valuable work, Emacs normally asks the user to confirm that it is ok
1477 to terminate them. Each process has a query flag which, if
1478 non-@code{nil}, says that Emacs should ask for confirmation before
1479 exiting and thus killing that process. The default for the query flag
1480 is @code{t}, meaning @emph{do} query.
1482 @defun process-query-on-exit-flag process
1483 This returns the query flag of @var{process}.
1486 @defun set-process-query-on-exit-flag process flag
1487 This function sets the query flag of @var{process} to @var{flag}. It
1492 ;; @r{Don't query about the shell process}
1493 (set-process-query-on-exit-flag (get-process "shell") nil)
1499 @defun process-kill-without-query process &optional do-query
1500 This function clears the query flag of @var{process}, so that
1501 Emacs will not query the user on account of that process.
1503 Actually, the function does more than that: it returns the old value of
1504 the process's query flag, and sets the query flag to @var{do-query}.
1505 Please don't use this function to do those things any more---please
1506 use the newer, cleaner functions @code{process-query-on-exit-flag} and
1507 @code{set-process-query-on-exit-flag} in all but the simplest cases.
1508 The only way you should use @code{process-kill-without-query} nowadays
1513 ;; @r{Don't query about the shell process}
1514 (process-kill-without-query (get-process "shell"))
1519 @node Transaction Queues
1520 @section Transaction Queues
1521 @cindex transaction queue
1523 You can use a @dfn{transaction queue} to communicate with a subprocess
1524 using transactions. First use @code{tq-create} to create a transaction
1525 queue communicating with a specified process. Then you can call
1526 @code{tq-enqueue} to send a transaction.
1528 @defun tq-create process
1529 This function creates and returns a transaction queue communicating with
1530 @var{process}. The argument @var{process} should be a subprocess
1531 capable of sending and receiving streams of bytes. It may be a child
1532 process, or it may be a TCP connection to a server, possibly on another
1536 @defun tq-enqueue queue question regexp closure fn &optional delay-question
1537 This function sends a transaction to queue @var{queue}. Specifying the
1538 queue has the effect of specifying the subprocess to talk to.
1540 The argument @var{question} is the outgoing message that starts the
1541 transaction. The argument @var{fn} is the function to call when the
1542 corresponding answer comes back; it is called with two arguments:
1543 @var{closure}, and the answer received.
1545 The argument @var{regexp} is a regular expression that should match
1546 text at the end of the entire answer, but nothing before; that's how
1547 @code{tq-enqueue} determines where the answer ends.
1549 If the argument @var{delay-question} is non-nil, delay sending this
1550 question until the process has finished replying to any previous
1551 questions. This produces more reliable results with some processes.
1553 The return value of @code{tq-enqueue} itself is not meaningful.
1556 @defun tq-close queue
1557 Shut down transaction queue @var{queue}, waiting for all pending transactions
1558 to complete, and then terminate the connection or child process.
1561 Transaction queues are implemented by means of a filter function.
1562 @xref{Filter Functions}.
1565 @section Network Connections
1566 @cindex network connection
1570 Emacs Lisp programs can open stream (TCP) and datagram (UDP) network
1571 connections to other processes on the same machine or other machines.
1572 A network connection is handled by Lisp much like a subprocess, and is
1573 represented by a process object. However, the process you are
1574 communicating with is not a child of the Emacs process, so it has no
1575 process @acronym{ID}, and you can't kill it or send it signals. All you
1576 can do is send and receive data. @code{delete-process} closes the
1577 connection, but does not kill the program at the other end; that
1578 program must decide what to do about closure of the connection.
1580 Lisp programs can listen for connections by creating network
1581 servers. A network server is also represented by a kind of process
1582 object, but unlike a network connection, the network server never
1583 transfers data itself. When it receives a connection request, it
1584 creates a new network connection to represent the connection just
1585 made. (The network connection inherits certain information, including
1586 the process plist, from the server.) The network server then goes
1587 back to listening for more connection requests.
1589 Network connections and servers are created by calling
1590 @code{make-network-process} with an argument list consisting of
1591 keyword/argument pairs, for example @code{:server t} to create a
1592 server process, or @code{:type 'datagram} to create a datagram
1593 connection. @xref{Low-Level Network}, for details. You can also use
1594 the @code{open-network-stream} function described below.
1596 You can distinguish process objects representing network connections
1597 and servers from those representing subprocesses with the
1598 @code{process-status} function. The possible status values for
1599 network connections are @code{open}, @code{closed}, @code{connect},
1600 and @code{failed}. For a network server, the status is always
1601 @code{listen}. None of those values is possible for a real
1602 subprocess. @xref{Process Information}.
1604 You can stop and resume operation of a network process by calling
1605 @code{stop-process} and @code{continue-process}. For a server
1606 process, being stopped means not accepting new connections. (Up to 5
1607 connection requests will be queued for when you resume the server; you
1608 can increase this limit, unless it is imposed by the operating
1609 system.) For a network stream connection, being stopped means not
1610 processing input (any arriving input waits until you resume the
1611 connection). For a datagram connection, some number of packets may be
1612 queued but input may be lost. You can use the function
1613 @code{process-command} to determine whether a network connection or
1614 server is stopped; a non-@code{nil} value means yes.
1616 @defun open-network-stream name buffer-or-name host service
1617 This function opens a TCP connection, and returns a process object
1618 that represents the connection.
1620 The @var{name} argument specifies the name for the process object. It
1621 is modified as necessary to make it unique.
1623 The @var{buffer-or-name} argument is the buffer to associate with the
1624 connection. Output from the connection is inserted in the buffer,
1625 unless you specify a filter function to handle the output. If
1626 @var{buffer-or-name} is @code{nil}, it means that the connection is not
1627 associated with any buffer.
1629 The arguments @var{host} and @var{service} specify where to connect to;
1630 @var{host} is the host name (a string), and @var{service} is the name of
1631 a defined network service (a string) or a port number (an integer).
1634 @defun process-contact process &optional key
1635 This function returns information about how a network process was set
1636 up. For a connection, when @var{key} is @code{nil}, it returns
1637 @code{(@var{hostname} @var{service})} which specifies what you
1640 If @var{key} is @code{t}, the value is the complete status information
1641 for the connection or server; that is, the list of keywords and values
1642 specified in @code{make-network-process}, except that some of the
1643 values represent the current status instead of what you specified:
1647 The associated value is the process buffer.
1649 The associated value is the process filter function.
1651 The associated value is the process sentinel function.
1653 In a connection, the address in internal format of the remote peer.
1655 The local address, in internal format.
1657 In a server, if you specified @code{t} for @var{service},
1658 this value is the actual port number.
1661 @code{:local} and @code{:remote} are included even if they were not
1662 specified explicitly in @code{make-network-process}.
1664 If @var{key} is a keyword, the function returns the value corresponding
1667 For an ordinary child process, this function always returns @code{t}.
1670 @node Network Servers
1671 @section Network Servers
1672 @cindex network servers
1674 You create a server by calling @code{make-network-process} with
1675 @code{:server t}. The server will listen for connection requests from
1676 clients. When it accepts a client connection request, that creates a
1677 new network connection, itself a process object, with the following
1682 The connection's process name is constructed by concatenating the
1683 server process' @var{name} with a client identification string. The
1684 client identification string for an IPv4 connection looks like
1685 @samp{<@var{a}.@var{b}.@var{c}.@var{d}:@var{p}>}. Otherwise, it is a
1686 unique number in brackets, as in @samp{<@var{nnn}>}. The number
1687 is unique for each connection in the Emacs session.
1690 If the server's filter is non-@code{nil}, the connection process does
1691 not get a separate process buffer; otherwise, Emacs creates a new
1692 buffer for the purpose. The buffer name is the server's buffer name
1693 or process name, concatenated with the client identification string.
1695 The server's process buffer value is never used directly by Emacs, but
1696 it is passed to the log function, which can log connections by
1697 inserting text there.
1700 The communication type and the process filter and sentinel are
1701 inherited from those of the server. The server never directly
1702 uses its filter and sentinel; their sole purpose is to initialize
1703 connections made to the server.
1706 The connection's process contact info is set according to the client's
1707 addressing information (typically an IP address and a port number).
1708 This information is associated with the @code{process-contact}
1709 keywords @code{:host}, @code{:service}, @code{:remote}.
1712 The connection's local address is set up according to the port
1713 number used for the connection.
1716 The client process' plist is initialized from the server's plist.
1723 A datagram connection communicates with individual packets rather
1724 than streams of data. Each call to @code{process-send} sends one
1725 datagram packet (@pxref{Input to Processes}), and each datagram
1726 received results in one call to the filter function.
1728 The datagram connection doesn't have to talk with the same remote
1729 peer all the time. It has a @dfn{remote peer address} which specifies
1730 where to send datagrams to. Each time an incoming datagram is passed
1731 to the filter function, the peer address is set to the address that
1732 datagram came from; that way, if the filter function sends a datagram,
1733 it will go back to that place. You can specify the remote peer
1734 address when you create the datagram connection using the
1735 @code{:remote} keyword. You can change it later on by calling
1736 @code{set-process-datagram-address}.
1738 @defun process-datagram-address process
1739 If @var{process} is a datagram connection or server, this function
1740 returns its remote peer address.
1743 @defun set-process-datagram-address process address
1744 If @var{process} is a datagram connection or server, this function
1745 sets its remote peer address to @var{address}.
1748 @node Low-Level Network
1749 @section Low-Level Network Access
1751 You can also create network connections by operating at a lower
1752 level than that of @code{open-network-stream}, using
1753 @code{make-network-process}.
1756 * Proc: Network Processes. Using @code{make-network-process}.
1757 * Options: Network Options. Further control over network connections.
1758 * Features: Network Feature Testing.
1759 Determining which network features work on
1760 the machine you are using.
1763 @node Network Processes
1764 @subsection @code{make-network-process}
1766 The basic function for creating network connections and network
1767 servers is @code{make-network-process}. It can do either of those
1768 jobs, depending on the arguments you give it.
1770 @defun make-network-process &rest args
1771 This function creates a network connection or server and returns the
1772 process object that represents it. The arguments @var{args} are a
1773 list of keyword/argument pairs. Omitting a keyword is always
1774 equivalent to specifying it with value @code{nil}, except for
1775 @code{:coding}, @code{:filter-multibyte}, and @code{:reuseaddr}. Here
1776 are the meaningful keywords:
1779 @item :name @var{name}
1780 Use the string @var{name} as the process name. It is modified if
1781 necessary to make it unique.
1783 @item :type @var{type}
1784 Specify the communication type. A value of @code{nil} specifies a
1785 stream connection (the default); @code{datagram} specifies a datagram
1786 connection. Both connections and servers can be of either type.
1788 @item :server @var{server-flag}
1789 If @var{server-flag} is non-@code{nil}, create a server. Otherwise,
1790 create a connection. For a stream type server, @var{server-flag} may
1791 be an integer which then specifies the length of the queue of pending
1792 connections to the server. The default queue length is 5.
1794 @item :host @var{host}
1795 Specify the host to connect to. @var{host} should be a host name or
1796 Internet address, as a string, or the symbol @code{local} to specify
1797 the local host. If you specify @var{host} for a server, it must
1798 specify a valid address for the local host, and only clients
1799 connecting to that address will be accepted.
1801 @item :service @var{service}
1802 @var{service} specifies a port number to connect to, or, for a server,
1803 the port number to listen on. It should be a service name that
1804 translates to a port number, or an integer specifying the port number
1805 directly. For a server, it can also be @code{t}, which means to let
1806 the system select an unused port number.
1808 @item :family @var{family}
1809 @var{family} specifies the address (and protocol) family for
1810 communication. @code{nil} means determine the proper address family
1811 automatically for the given @var{host} and @var{service}.
1812 @code{local} specifies a Unix socket, in which case @var{host} is
1813 ignored. @code{ipv4} and @code{ipv6} specify to use IPv4 and IPv6
1816 @item :local @var{local-address}
1817 For a server process, @var{local-address} is the address to listen on.
1818 It overrides @var{family}, @var{host} and @var{service}, and you
1819 may as well not specify them.
1821 @item :remote @var{remote-address}
1822 For a connection, @var{remote-address} is the address to connect to.
1823 It overrides @var{family}, @var{host} and @var{service}, and you
1824 may as well not specify them.
1826 For a datagram server, @var{remote-address} specifies the initial
1827 setting of the remote datagram address.
1829 The format of @var{local-address} or @var{remote-address} depends on
1834 An IPv4 address is represented as a five-element vector of four 8-bit
1835 integers and one 16-bit integer
1836 @code{[@var{a} @var{b} @var{c} @var{d} @var{p}]} corresponding to
1837 numeric IPv4 address @var{a}.@var{b}.@var{c}.@var{d} and port number
1841 An IPv6 address is represented as a nine-element vector of 16-bit
1842 integers @code{[@var{a} @var{b} @var{c} @var{d} @var{e} @var{f}
1843 @var{g} @var{h} @var{p}]} corresponding to numeric IPv6 address
1844 @var{a}:@var{b}:@var{c}:@var{d}:@var{e}:@var{f}:@var{g}:@var{h} and
1845 port number @var{p}.
1848 A local address is represented as a string which specifies the address
1849 in the local address space.
1852 An ``unsupported family'' address is represented by a cons
1853 @code{(@var{f} . @var{av})}, where @var{f} is the family number and
1854 @var{av} is a vector specifying the socket address using one element
1855 per address data byte. Do not rely on this format in portable code,
1856 as it may depend on implementation defined constants, data sizes, and
1857 data structure alignment.
1860 @item :nowait @var{bool}
1861 If @var{bool} is non-@code{nil} for a stream connection, return
1862 without waiting for the connection to complete. When the connection
1863 succeeds or fails, Emacs will call the sentinel function, with a
1864 second argument matching @code{"open"} (if successful) or
1865 @code{"failed"}. The default is to block, so that
1866 @code{make-network-process} does not return until the connection
1867 has succeeded or failed.
1869 @item :stop @var{stopped}
1870 Start the network connection or server in the `stopped' state if
1871 @var{stopped} is non-@code{nil}.
1873 @item :buffer @var{buffer}
1874 Use @var{buffer} as the process buffer.
1876 @item :coding @var{coding}
1877 Use @var{coding} as the coding system for this process. To specify
1878 different coding systems for decoding data from the connection and for
1879 encoding data sent to it, specify @code{(@var{decoding} .
1880 @var{encoding})} for @var{coding}.
1882 If you don't specify this keyword at all, the default
1883 is to determine the coding systems from the data.
1885 @item :noquery @var{query-flag}
1886 Initialize the process query flag to @var{query-flag}.
1887 @xref{Query Before Exit}.
1889 @item :filter @var{filter}
1890 Initialize the process filter to @var{filter}.
1892 @item :filter-multibyte @var{bool}
1893 If @var{bool} is non-@code{nil}, strings given to the process filter
1894 are multibyte, otherwise they are unibyte. If you don't specify this
1895 keyword at all, the default is that the strings are multibyte if
1896 @code{default-enable-multibyte-characters} is non-@code{nil}.
1898 @item :sentinel @var{sentinel}
1899 Initialize the process sentinel to @var{sentinel}.
1901 @item :log @var{log}
1902 Initialize the log function of a server process to @var{log}. The log
1903 function is called each time the server accepts a network connection
1904 from a client. The arguments passed to the log function are
1905 @var{server}, @var{connection}, and @var{message}, where @var{server}
1906 is the server process, @var{connection} is the new process for the
1907 connection, and @var{message} is a string describing what has
1910 @item :plist @var{plist}
1911 Initialize the process plist to @var{plist}.
1914 The original argument list, modified with the actual connection
1915 information, is available via the @code{process-contact} function.
1918 @node Network Options
1919 @subsection Network Options
1921 The following network options can be specified when you create a
1922 network process. Except for @code{:reuseaddr}, you can also set or
1923 modify these options later, using @code{set-network-process-option}.
1925 For a server process, the options specified with
1926 @code{make-network-process} are not inherited by the client
1927 connections, so you will need to set the necessary options for each
1928 child connection as it is created.
1931 @item :bindtodevice @var{device-name}
1932 If @var{device-name} is a non-empty string identifying a network
1933 interface name (see @code{network-interface-list}), only handle
1934 packets received on that interface. If @var{device-name} is @code{nil}
1935 (the default), handle packets received on any interface.
1937 Using this option may require special privileges on some systems.
1939 @item :broadcast @var{broadcast-flag}
1940 If @var{broadcast-flag} is non-@code{nil} for a datagram process, the
1941 process will receive datagram packet sent to a broadcast address, and
1942 be able to send packets to a broadcast address. Ignored for a stream
1945 @item :dontroute @var{dontroute-flag}
1946 If @var{dontroute-flag} is non-@code{nil}, the process can only send
1947 to hosts on the same network as the local host.
1949 @item :keepalive @var{keepalive-flag}
1950 If @var{keepalive-flag} is non-@code{nil} for a stream connection,
1951 enable exchange of low-level keep-alive messages.
1953 @item :linger @var{linger-arg}
1954 If @var{linger-arg} is non-@code{nil}, wait for successful
1955 transmission of all queued packets on the connection before it is
1956 deleted (see @code{delete-process}). If @var{linger-arg} is an
1957 integer, it specifies the maximum time in seconds to wait for queued
1958 packets to be sent before closing the connection. Default is
1959 @code{nil} which means to discard unsent queued packets when the
1962 @item :oobinline @var{oobinline-flag}
1963 If @var{oobinline-flag} is non-@code{nil} for a stream connection,
1964 receive out-of-band data in the normal data stream. Otherwise, ignore
1967 @item :priority @var{priority}
1968 Set the priority for packets sent on this connection to the integer
1969 @var{priority}. The interpretation of this number is protocol
1970 specific, such as setting the TOS (type of service) field on IP
1971 packets sent on this connection. It may also have system dependent
1972 effects, such as selecting a specific output queue on the network
1975 @item :reuseaddr @var{reuseaddr-flag}
1976 If @var{reuseaddr-flag} is non-@code{nil} (the default) for a stream
1977 server process, allow this server to reuse a specific port number (see
1978 @code{:service}) unless another process on this host is already
1979 listening on that port. If @var{reuseaddr-flag} is @code{nil}, there
1980 may be a period of time after the last use of that port (by any
1981 process on the host), where it is not possible to make a new server on
1985 @defun set-network-process-option process option value
1986 This function sets or modifies a network option for network process
1987 @var{process}. See @code{make-network-process} for details of options
1988 @var{option} and their corresponding values @var{value}.
1990 The current setting of an option is available via the
1991 @code{process-contact} function.
1994 @node Network Feature Testing
1995 @subsection Testing Availability of Network Features
1997 To test for the availability of a given network feature, use
1998 @code{featurep} like this:
2001 (featurep 'make-network-process '(@var{keyword} @var{value}))
2005 The result of the first form is @code{t} if it works to specify
2006 @var{keyword} with value @var{value} in @code{make-network-process}.
2007 The result of the second form is @code{t} if @var{keyword} is
2008 supported by @code{make-network-process}. Here are some of the
2009 @var{keyword}---@var{value} pairs you can test in
2014 Non-@code{nil} if non-blocking connect is supported.
2015 @item (:type datagram)
2016 Non-@code{nil} if datagrams are supported.
2017 @item (:family local)
2018 Non-@code{nil} if local (a.k.a.@: ``UNIX domain'') sockets are supported.
2019 @item (:family ipv6)
2020 Non-@code{nil} if IPv6 is supported.
2022 Non-@code{nil} if the system can select the port for a server.
2025 To test for the availability of a given network option, use
2026 @code{featurep} like this:
2029 (featurep 'make-network-process '@var{keyword})
2033 Here are some of the options you can test in this way.
2044 That particular network option is supported by
2045 @code{make-network-process} and @code{set-network-process-option}.
2049 @section Misc Network Facilities
2051 These additional functions are useful for creating and operating
2052 on network connections. Note that they are supported only on some
2055 @defun network-interface-list
2056 This function returns a list describing the network interfaces
2057 of the machine you are using. The value is an alist whose
2058 elements have the form @code{(@var{name} . @var{address})}.
2059 @var{address} has the same form as the @var{local-address}
2060 and @var{remote-address} arguments to @code{make-network-process}.
2063 @defun network-interface-info ifname
2064 This function returns information about the network interface named
2065 @var{ifname}. The value is a list of the form
2066 @code{(@var{addr} @var{bcast} @var{netmask} @var{hwaddr} @var{flags})}.
2070 The Internet protocol address.
2072 The broadcast address.
2076 The layer 2 address (Ethernet MAC address, for instance).
2078 The current flags of the interface.
2082 @defun format-network-address address &optional omit-port
2083 This function converts the Lisp representation of a network address to
2086 A five-element vector @code{[@var{a} @var{b} @var{c} @var{d} @var{p}]}
2087 represents an IPv4 address @var{a}.@var{b}.@var{c}.@var{d} and port
2088 number @var{p}. @code{format-network-address} converts that to the
2089 string @code{"@var{a}.@var{b}.@var{c}.@var{d}:@var{p}"}.
2091 A nine-element vector @code{[@var{a} @var{b} @var{c} @var{d} @var{e}
2092 @var{f} @var{g} @var{h} @var{p}]} represents an IPv6 address along
2093 with a port number. @code{format-network-address} converts that to
2095 @code{"[@var{a}:@var{b}:@var{c}:@var{d}:@var{e}:@var{f}:@var{g}:@var{h}]:@var{p}"}.
2097 If the vector does not include the port number, @var{p}, or if
2098 @var{omit-port} is non-@code{nil}, the result does not include the
2099 @code{:@var{p}} suffix.
2103 @section Packing and Unpacking Byte Arrays
2104 @cindex byte packing and unpacking
2106 This section describes how to pack and unpack arrays of bytes,
2107 usually for binary network protocols. These functions convert byte arrays
2108 to alists, and vice versa. The byte array can be represented as a
2109 unibyte string or as a vector of integers, while the alist associates
2110 symbols either with fixed-size objects or with recursive sub-alists.
2113 @cindex deserializing
2116 Conversion from byte arrays to nested alists is also known as
2117 @dfn{deserializing} or @dfn{unpacking}, while going in the opposite
2118 direction is also known as @dfn{serializing} or @dfn{packing}.
2121 * Bindat Spec:: Describing data layout.
2122 * Bindat Functions:: Doing the unpacking and packing.
2123 * Bindat Examples:: Samples of what bindat.el can do for you!
2127 @subsection Describing Data Layout
2129 To control unpacking and packing, you write a @dfn{data layout
2130 specification}, a special nested list describing named and typed
2131 @dfn{fields}. This specification controls length of each field to be
2132 processed, and how to pack or unpack it. We normally keep bindat specs
2133 in variables whose names end in @samp{-bindat-spec}; that kind of name
2134 is automatically recognized as ``risky.''
2138 @cindex little endian
2139 @cindex network byte ordering
2140 A field's @dfn{type} describes the size (in bytes) of the object
2141 that the field represents and, in the case of multibyte fields, how
2142 the bytes are ordered within the field. The two possible orderings
2143 are ``big endian'' (also known as ``network byte ordering'') and
2144 ``little endian.'' For instance, the number @code{#x23cd} (decimal
2145 9165) in big endian would be the two bytes @code{#x23} @code{#xcd};
2146 and in little endian, @code{#xcd} @code{#x23}. Here are the possible
2152 Unsigned byte, with length 1.
2157 Unsigned integer in network byte order, with length 2.
2160 Unsigned integer in network byte order, with length 3.
2165 Unsigned integer in network byte order, with length 4.
2166 Note: These values may be limited by Emacs' integer implementation limits.
2171 Unsigned integer in little endian order, with length 2, 3 and 4, respectively.
2174 String of length @var{len}.
2176 @item strz @var{len}
2177 Zero-terminated string, in a fixed-size field with length @var{len}.
2179 @item vec @var{len} [@var{type}]
2180 Vector of @var{len} elements of type @var{type}, or bytes if not
2181 @var{type} is specified.
2182 The @var{type} is any of the simple types above, or another vector
2183 specified as a list @code{(vec @var{len} [@var{type}])}.
2186 Four-byte vector representing an Internet address. For example:
2187 @code{[127 0 0 1]} for localhost.
2189 @item bits @var{len}
2190 List of set bits in @var{len} bytes. The bytes are taken in big
2191 endian order and the bits are numbered starting with @code{8 *
2192 @var{len} @minus{} 1} and ending with zero. For example: @code{bits
2193 2} unpacks @code{#x28} @code{#x1c} to @code{(2 3 4 11 13)} and
2194 @code{#x1c} @code{#x28} to @code{(3 5 10 11 12)}.
2196 @item (eval @var{form})
2197 @var{form} is a Lisp expression evaluated at the moment the field is
2198 unpacked or packed. The result of the evaluation should be one of the
2199 above-listed type specifications.
2202 For a fixed-size field, the length @var{len} is given as an integer
2203 specifying the number of bytes in the field.
2205 When the length of a field is not fixed, it typically depends on the
2206 value of a preceding field. In this case, the length @var{len} can be
2207 given either as a list @code{(@var{name} ...)} identifying a
2208 @dfn{field name} in the format specified for @code{bindat-get-field}
2209 below, or by an expression @code{(eval @var{form})} where @var{form}
2210 should evaluate to an integer, specifying the field length.
2212 A field specification generally has the form @code{([@var{name}]
2213 @var{handler})}. The square braces indicate that @var{name} is
2214 optional. (Don't use names that are symbols meaningful as type
2215 specifications (above) or handler specifications (below), since that
2216 would be ambiguous.) @var{name} can be a symbol or the expression
2217 @code{(eval @var{form})}, in which case @var{form} should evaluate to
2220 @var{handler} describes how to unpack or pack the field and can be one
2225 Unpack/pack this field according to the type specification @var{type}.
2227 @item eval @var{form}
2228 Evaluate @var{form}, a Lisp expression, for side-effect only. If the
2229 field name is specified, the value is bound to that field name.
2231 @item fill @var{len}
2232 Skip @var{len} bytes. In packing, this leaves them unchanged,
2233 which normally means they remain zero. In unpacking, this means
2236 @item align @var{len}
2237 Skip to the next multiple of @var{len} bytes.
2239 @item struct @var{spec-name}
2240 Process @var{spec-name} as a sub-specification. This describes a
2241 structure nested within another structure.
2243 @item union @var{form} (@var{tag} @var{spec})@dots{}
2244 @c ??? I don't see how one would actually use this.
2245 @c ??? what kind of expression would be useful for @var{form}?
2246 Evaluate @var{form}, a Lisp expression, find the first @var{tag}
2247 that matches it, and process its associated data layout specification
2248 @var{spec}. Matching can occur in one of three ways:
2252 If a @var{tag} has the form @code{(eval @var{expr})}, evaluate
2253 @var{expr} with the variable @code{tag} dynamically bound to the value
2254 of @var{form}. A non-@code{nil} result indicates a match.
2257 @var{tag} matches if it is @code{equal} to the value of @var{form}.
2260 @var{tag} matches unconditionally if it is @code{t}.
2263 @item repeat @var{count} @var{field-specs}@dots{}
2264 Process the @var{field-specs} recursively, in order, then repeat
2265 starting from the first one, processing all the specs @var{count}
2266 times overall. The @var{count} is given using the same formats as a
2267 field length---if an @code{eval} form is used, it is evaluated just once.
2268 For correct operation, each spec in @var{field-specs} must include a name.
2271 For the @code{(eval @var{form})} forms used in a bindat specification,
2272 the @var{form} can access and update these dynamically bound variables
2277 Value of the last field processed.
2280 The data as a byte array.
2283 Current index (within @code{bindat-raw}) for unpacking or packing.
2286 The alist containing the structured data that have been unpacked so
2287 far, or the entire structure being packed. You can use
2288 @code{bindat-get-field} to access specific fields of this structure.
2292 Inside a @code{repeat} block, these contain the maximum number of
2293 repetitions (as specified by the @var{count} parameter), and the
2294 current repetition number (counting from 0). Setting @code{count} to
2295 zero will terminate the inner-most repeat block after the current
2296 repetition has completed.
2299 @node Bindat Functions
2300 @subsection Functions to Unpack and Pack Bytes
2302 In the following documentation, @var{spec} refers to a data layout
2303 specification, @code{bindat-raw} to a byte array, and @var{struct} to an
2304 alist representing unpacked field data.
2306 @defun bindat-unpack spec bindat-raw &optional bindat-idx
2307 This function unpacks data from the unibyte string or byte
2308 array @code{bindat-raw}
2309 according to @var{spec}. Normally this starts unpacking at the
2310 beginning of the byte array, but if @var{bindat-idx} is non-@code{nil}, it
2311 specifies a zero-based starting position to use instead.
2313 The value is an alist or nested alist in which each element describes
2317 @defun bindat-get-field struct &rest name
2318 This function selects a field's data from the nested alist
2319 @var{struct}. Usually @var{struct} was returned by
2320 @code{bindat-unpack}. If @var{name} corresponds to just one argument,
2321 that means to extract a top-level field value. Multiple @var{name}
2322 arguments specify repeated lookup of sub-structures. An integer name
2323 acts as an array index.
2325 For example, if @var{name} is @code{(a b 2 c)}, that means to find
2326 field @code{c} in the third element of subfield @code{b} of field
2327 @code{a}. (This corresponds to @code{struct.a.b[2].c} in C.)
2330 Although packing and unpacking operations change the organization of
2331 data (in memory), they preserve the data's @dfn{total length}, which is
2332 the sum of all the fields' lengths, in bytes. This value is not
2333 generally inherent in either the specification or alist alone; instead,
2334 both pieces of information contribute to its calculation. Likewise, the
2335 length of a string or array being unpacked may be longer than the data's
2336 total length as described by the specification.
2338 @defun bindat-length spec struct
2339 This function returns the total length of the data in @var{struct},
2340 according to @var{spec}.
2343 @defun bindat-pack spec struct &optional bindat-raw bindat-idx
2344 This function returns a byte array packed according to @var{spec} from
2345 the data in the alist @var{struct}. Normally it creates and fills a
2346 new byte array starting at the beginning. However, if @var{bindat-raw}
2347 is non-@code{nil}, it specifies a pre-allocated unibyte string or vector to
2348 pack into. If @var{bindat-idx} is non-@code{nil}, it specifies the starting
2349 offset for packing into @code{bindat-raw}.
2351 When pre-allocating, you should make sure @code{(length @var{bindat-raw})}
2352 meets or exceeds the total length to avoid an out-of-range error.
2355 @defun bindat-ip-to-string ip
2356 Convert the Internet address vector @var{ip} to a string in the usual
2360 (bindat-ip-to-string [127 0 0 1])
2361 @result{} "127.0.0.1"
2365 @node Bindat Examples
2366 @subsection Examples of Byte Unpacking and Packing
2368 Here is a complete example of byte unpacking and packing:
2371 (defvar fcookie-index-spec
2379 (:offset repeat (:count)
2381 "Description of a fortune cookie index file's contents.")
2383 (defun fcookie (cookies &optional index)
2384 "Display a random fortune cookie from file COOKIES.
2385 Optional second arg INDEX specifies the associated index
2386 filename, which is by default constructed by appending
2387 \".dat\" to COOKIES. Display cookie text in possibly
2388 new buffer \"*Fortune Cookie: BASENAME*\" where BASENAME
2389 is COOKIES without the directory part."
2390 (interactive "fCookies file: ")
2391 (let* ((info (with-temp-buffer
2392 (insert-file-contents-literally
2393 (or index (concat cookies ".dat")))
2394 (bindat-unpack fcookie-index-spec
2396 (sel (random (bindat-get-field info :count)))
2397 (beg (cdar (bindat-get-field info :offset sel)))
2398 (end (or (cdar (bindat-get-field info
2400 (nth 7 (file-attributes cookies)))))
2403 (format "*Fortune Cookie: %s*"
2404 (file-name-nondirectory cookies))))
2406 (insert-file-contents-literally
2407 cookies nil beg (- end 3))))
2409 (defun fcookie-create-index (cookies &optional index delim)
2410 "Scan file COOKIES, and write out its index file.
2411 Optional second arg INDEX specifies the index filename,
2412 which is by default constructed by appending \".dat\" to
2413 COOKIES. Optional third arg DELIM specifies the unibyte
2414 character which, when found on a line of its own in
2415 COOKIES, indicates the border between entries."
2416 (interactive "fCookies file: ")
2417 (setq delim (or delim ?%))
2418 (let ((delim-line (format "\n%c\n" delim))
2421 min p q len offsets)
2422 (unless (= 3 (string-bytes delim-line))
2423 (error "Delimiter cannot be represented in one byte"))
2425 (insert-file-contents-literally cookies)
2426 (while (and (setq p (point))
2427 (search-forward delim-line (point-max) t)
2428 (setq len (- (point) 3 p)))
2429 (setq count (1+ count)
2431 min (min (or min max) len)
2432 offsets (cons (1- p) offsets))))
2434 (set-buffer-multibyte nil)
2444 (:offset . ,(mapcar (lambda (o)
2445 (list (cons :foo o)))
2446 (nreverse offsets))))))
2447 (let ((coding-system-for-write 'raw-text-unix))
2448 (write-file (or index (concat cookies ".dat")))))))
2451 Following is an example of defining and unpacking a complex structure.
2452 Consider the following C structures:
2456 unsigned long dest_ip;
2457 unsigned long src_ip;
2458 unsigned short dest_port;
2459 unsigned short src_port;
2464 unsigned char opcode;
2465 unsigned short length; /* In network byte order */
2466 unsigned char id[8]; /* null-terminated string */
2467 unsigned char data[/* (length + 3) & ~3 */];
2471 struct header header;
2472 unsigned long counters[2]; /* In little endian order */
2473 unsigned char items;
2474 unsigned char filler[3];
2475 struct data item[/* items */];
2480 The corresponding data layout specification:
2492 (length u16) ;; network byte order
2498 '((header struct header-spec)
2499 (counters vec 2 u32r) ;; little endian order
2502 (item repeat (items)
2503 (struct data-spec))))
2506 A binary data representation:
2510 [ 192 168 1 100 192 168 1 101 01 28 21 32
2511 160 134 1 0 5 1 0 0 2 0 0 0
2512 2 3 0 5 ?A ?B ?C ?D ?E ?F 0 0 1 2 3 4 5 0 0 0
2513 1 4 0 7 ?B ?C ?D ?E ?F ?G 0 0 6 7 8 9 10 11 12 0 ])
2516 The corresponding decoded structure:
2519 (setq decoded (bindat-unpack packet-spec binary-data))
2522 (dest-ip . [192 168 1 100])
2523 (src-ip . [192 168 1 101])
2526 (counters . [100000 261])
2528 (item ((data . [1 2 3 4 5])
2533 ((data . [6 7 8 9 10 11 12])
2540 Fetching data from this structure:
2543 (bindat-get-field decoded 'item 1 'id)
2548 arch-tag: ba9da253-e65f-4e7f-b727-08fba0a1df7a