2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2012
4 @c Free Software Foundation, Inc.
5 @c See the file elisp.texi for copying conditions.
6 @node Processes, Display, Abbrevs, Top
13 In the terminology of operating systems, a @dfn{process} is a space in
14 which a program can execute. Emacs runs in a process. Emacs Lisp
15 programs can invoke other programs in processes of their own. These are
16 called @dfn{subprocesses} or @dfn{child processes} of the Emacs process,
17 which is their @dfn{parent process}.
19 A subprocess of Emacs may be @dfn{synchronous} or @dfn{asynchronous},
20 depending on how it is created. When you create a synchronous
21 subprocess, the Lisp program waits for the subprocess to terminate
22 before continuing execution. When you create an asynchronous
23 subprocess, it can run in parallel with the Lisp program. This kind of
24 subprocess is represented within Emacs by a Lisp object which is also
25 called a ``process''. Lisp programs can use this object to communicate
26 with the subprocess or to control it. For example, you can send
27 signals, obtain status information, receive output from the process, or
30 @defun processp object
31 This function returns @code{t} if @var{object} represents an Emacs
32 subprocess, @code{nil} otherwise.
35 In addition to subprocesses of the current Emacs session, you can
36 also access other processes running on your machine. @xref{System
40 * Subprocess Creation:: Functions that start subprocesses.
41 * Shell Arguments:: Quoting an argument to pass it to a shell.
42 * Synchronous Processes:: Details of using synchronous subprocesses.
43 * Asynchronous Processes:: Starting up an asynchronous subprocess.
44 * Deleting Processes:: Eliminating an asynchronous subprocess.
45 * Process Information:: Accessing run-status and other attributes.
46 * Input to Processes:: Sending input to an asynchronous subprocess.
47 * Signals to Processes:: Stopping, continuing or interrupting
48 an asynchronous subprocess.
49 * Output from Processes:: Collecting output from an asynchronous subprocess.
50 * Sentinels:: Sentinels run when process run-status changes.
51 * Query Before Exit:: Whether to query if exiting will kill a process.
52 * System Processes:: Accessing other processes running on your system.
53 * Transaction Queues:: Transaction-based communication with subprocesses.
54 * Network:: Opening network connections.
55 * Network Servers:: Network servers let Emacs accept net connections.
56 * Datagrams:: UDP network connections.
57 * Low-Level Network:: Lower-level but more general function
58 to create connections and servers.
59 * Misc Network:: Additional relevant functions for net connections.
60 * Serial Ports:: Communicating with serial ports.
61 * Byte Packing:: Using bindat to pack and unpack binary data.
64 @node Subprocess Creation
65 @section Functions that Create Subprocesses
67 There are three primitives that create a new subprocess in which to run
68 a program. One of them, @code{start-process}, creates an asynchronous
69 process and returns a process object (@pxref{Asynchronous Processes}).
70 The other two, @code{call-process} and @code{call-process-region},
71 create a synchronous process and do not return a process object
72 (@pxref{Synchronous Processes}). There are various higher-level
73 functions that make use of these primitives to run particular types of
76 Synchronous and asynchronous processes are explained in the following
77 sections. Since the three functions are all called in a similar
78 fashion, their common arguments are described here.
80 @cindex execute program
81 @cindex @env{PATH} environment variable
82 @cindex @env{HOME} environment variable
83 In all cases, the function's @var{program} argument specifies the
84 program to be run. An error is signaled if the file is not found or
85 cannot be executed. If the file name is relative, the variable
86 @code{exec-path} contains a list of directories to search. Emacs
87 initializes @code{exec-path} when it starts up, based on the value of
88 the environment variable @env{PATH}. The standard file name
89 constructs, @samp{~}, @samp{.}, and @samp{..}, are interpreted as
90 usual in @code{exec-path}, but environment variable substitutions
91 (@samp{$HOME}, etc.) are not recognized; use
92 @code{substitute-in-file-name} to perform them (@pxref{File Name
93 Expansion}). @code{nil} in this list refers to
94 @code{default-directory}.
96 Executing a program can also try adding suffixes to the specified
100 This variable is a list of suffixes (strings) to try adding to the
101 specified program file name. The list should include @code{""} if you
102 want the name to be tried exactly as specified. The default value is
106 @strong{Please note:} The argument @var{program} contains only the
107 name of the program; it may not contain any command-line arguments. You
108 must use a separate argument, @var{args}, to provide those, as
111 Each of the subprocess-creating functions has a @var{buffer-or-name}
112 argument that specifies where the standard output from the program will
113 go. It should be a buffer or a buffer name; if it is a buffer name,
114 that will create the buffer if it does not already exist. It can also
115 be @code{nil}, which says to discard the output unless a filter function
116 handles it. (@xref{Filter Functions}, and @ref{Read and Print}.)
117 Normally, you should avoid having multiple processes send output to the
118 same buffer because their output would be intermixed randomly.
119 For synchronous processes, you can send the output to a file instead
122 @cindex program arguments
123 All three of the subprocess-creating functions have a @code{&rest}
124 argument, @var{args}. The @var{args} must all be strings, and they are
125 supplied to @var{program} as separate command line arguments. Wildcard
126 characters and other shell constructs have no special meanings in these
127 strings, since the strings are passed directly to the specified program.
129 @cindex environment variables, subprocesses
130 The subprocess inherits its environment from Emacs, but you can
131 specify overrides for it with @code{process-environment}. @xref{System
132 Environment}. The subprocess gets its current directory from the
133 value of @code{default-directory}.
135 @defvar exec-directory
137 The value of this variable is a string, the name of a directory that
138 contains programs that come with GNU Emacs and are intended for Emacs
139 to invoke. The program @code{movemail} is an example of such a program;
140 Rmail uses it to fetch new mail from an inbox.
144 The value of this variable is a list of directories to search for
145 programs to run in subprocesses. Each element is either the name of a
146 directory (i.e., a string), or @code{nil}, which stands for the default
147 directory (which is the value of @code{default-directory}).
148 @cindex program directories
150 The value of @code{exec-path} is used by @code{call-process} and
151 @code{start-process} when the @var{program} argument is not an absolute
154 Generally, you should not modify @code{exec-path} directly. Instead,
155 ensure that your @env{PATH} environment variable is set appropriately
156 before starting Emacs. Trying to modify @code{exec-path}
157 independently of @env{PATH} can lead to confusing results.
160 @node Shell Arguments
161 @section Shell Arguments
162 @cindex arguments for shell commands
163 @cindex shell command arguments
165 Lisp programs sometimes need to run a shell and give it a command
166 that contains file names that were specified by the user. These
167 programs ought to be able to support any valid file name. But the shell
168 gives special treatment to certain characters, and if these characters
169 occur in the file name, they will confuse the shell. To handle these
170 characters, use the function @code{shell-quote-argument}:
172 @defun shell-quote-argument argument
173 This function returns a string that represents, in shell syntax,
174 an argument whose actual contents are @var{argument}. It should
175 work reliably to concatenate the return value into a shell command
176 and then pass it to a shell for execution.
178 Precisely what this function does depends on your operating system. The
179 function is designed to work with the syntax of your system's standard
180 shell; if you use an unusual shell, you will need to redefine this
184 ;; @r{This example shows the behavior on GNU and Unix systems.}
185 (shell-quote-argument "foo > bar")
186 @result{} "foo\\ \\>\\ bar"
188 ;; @r{This example shows the behavior on MS-DOS and MS-Windows.}
189 (shell-quote-argument "foo > bar")
190 @result{} "\"foo > bar\""
193 Here's an example of using @code{shell-quote-argument} to construct
198 (shell-quote-argument oldfile)
200 (shell-quote-argument newfile))
204 @cindex quoting and unquoting command-line arguments
205 @cindex minibuffer input, and command-line arguments
206 @cindex @code{call-process}, command-line arguments from minibuffer
207 @cindex @code{start-process}, command-line arguments from minibuffer
208 The following two functions are useful for combining a list of
209 individual command-line argument strings into a single string, and
210 taking a string apart into a list of individual command-line
211 arguments. These functions are mainly intended for
212 converting user input in the minibuffer, a Lisp string, into a list of
213 string arguments to be passed to @code{call-process} or
214 @code{start-process}, or for converting such lists of arguments into
215 a single Lisp string to be presented in the minibuffer or echo area.
217 @defun split-string-and-unquote string &optional separators
218 This function splits @var{string} into substrings at matches for the
219 regular expression @var{separators}, like @code{split-string} does
220 (@pxref{Creating Strings}); in addition, it removes quoting from the
221 substrings. It then makes a list of the substrings and returns it.
223 If @var{separators} is omitted or @code{nil}, it defaults to
224 @code{"\\s-+"}, which is a regular expression that matches one or more
225 characters with whitespace syntax (@pxref{Syntax Class Table}).
227 This function supports two types of quoting: enclosing a whole string
228 in double quotes @code{"@dots{}"}, and quoting individual characters
229 with a backslash escape @samp{\}. The latter is also used in Lisp
230 strings, so this function can handle those as well.
233 @defun combine-and-quote-strings list-of-strings &optional separator
234 This function concatenates @var{list-of-strings} into a single string,
235 quoting each string as necessary. It also sticks the @var{separator}
236 string between each pair of strings; if @var{separator} is omitted or
237 @code{nil}, it defaults to @code{" "}. The return value is the
240 The strings in @var{list-of-strings} that need quoting are those that
241 include @var{separator} as their substring. Quoting a string encloses
242 it in double quotes @code{"@dots{}"}. In the simplest case, if you
243 are consing a command from the individual command-line arguments,
244 every argument that includes embedded blanks will be quoted.
247 @node Synchronous Processes
248 @section Creating a Synchronous Process
249 @cindex synchronous subprocess
251 After a @dfn{synchronous process} is created, Emacs waits for the
252 process to terminate before continuing. Starting Dired on GNU or
253 Unix@footnote{On other systems, Emacs uses a Lisp emulation of
254 @code{ls}; see @ref{Contents of Directories}.} is an example of this: it
255 runs @code{ls} in a synchronous process, then modifies the output
256 slightly. Because the process is synchronous, the entire directory
257 listing arrives in the buffer before Emacs tries to do anything with it.
259 While Emacs waits for the synchronous subprocess to terminate, the
260 user can quit by typing @kbd{C-g}. The first @kbd{C-g} tries to kill
261 the subprocess with a @code{SIGINT} signal; but it waits until the
262 subprocess actually terminates before quitting. If during that time the
263 user types another @kbd{C-g}, that kills the subprocess instantly with
264 @code{SIGKILL} and quits immediately (except on MS-DOS, where killing
265 other processes doesn't work). @xref{Quitting}.
267 The synchronous subprocess functions return an indication of how the
270 The output from a synchronous subprocess is generally decoded using a
271 coding system, much like text read from a file. The input sent to a
272 subprocess by @code{call-process-region} is encoded using a coding
273 system, much like text written into a file. @xref{Coding Systems}.
275 @defun call-process program &optional infile destination display &rest args
276 This function calls @var{program} and waits for it to finish.
278 The current working directory of the subprocess is
279 @code{default-directory}.
281 The standard input for the new process comes from file @var{infile} if
282 @var{infile} is not @code{nil}, and from the null device otherwise.
283 The argument @var{destination} says where to put the process output.
284 Here are the possibilities:
288 Insert the output in that buffer, before point. This includes both the
289 standard output stream and the standard error stream of the process.
292 Insert the output in a buffer with that name, before point.
295 Insert the output in the current buffer, before point.
301 Discard the output, and return @code{nil} immediately without waiting
302 for the subprocess to finish.
304 In this case, the process is not truly synchronous, since it can run in
305 parallel with Emacs; but you can think of it as synchronous in that
306 Emacs is essentially finished with the subprocess as soon as this
309 MS-DOS doesn't support asynchronous subprocesses, so this option doesn't
312 @item @code{(:file @var{file-name})}
313 Send the output to the file name specified, overwriting it if it
316 @item @code{(@var{real-destination} @var{error-destination})}
317 Keep the standard output stream separate from the standard error stream;
318 deal with the ordinary output as specified by @var{real-destination},
319 and dispose of the error output according to @var{error-destination}.
320 If @var{error-destination} is @code{nil}, that means to discard the
321 error output, @code{t} means mix it with the ordinary output, and a
322 string specifies a file name to redirect error output into.
324 You can't directly specify a buffer to put the error output in; that is
325 too difficult to implement. But you can achieve this result by sending
326 the error output to a temporary file and then inserting the file into a
330 If @var{display} is non-@code{nil}, then @code{call-process} redisplays
331 the buffer as output is inserted. (However, if the coding system chosen
332 for decoding output is @code{undecided}, meaning deduce the encoding
333 from the actual data, then redisplay sometimes cannot continue once
334 non-@acronym{ASCII} characters are encountered. There are fundamental
335 reasons why it is hard to fix this; see @ref{Output from Processes}.)
337 Otherwise the function @code{call-process} does no redisplay, and the
338 results become visible on the screen only when Emacs redisplays that
339 buffer in the normal course of events.
341 The remaining arguments, @var{args}, are strings that specify command
342 line arguments for the program.
344 The value returned by @code{call-process} (unless you told it not to
345 wait) indicates the reason for process termination. A number gives the
346 exit status of the subprocess; 0 means success, and any other value
347 means failure. If the process terminated with a signal,
348 @code{call-process} returns a string describing the signal.
350 In the examples below, the buffer @samp{foo} is current.
354 (call-process "pwd" nil t)
357 ---------- Buffer: foo ----------
359 ---------- Buffer: foo ----------
363 (call-process "grep" nil "bar" nil "lewis" "/etc/passwd")
366 ---------- Buffer: bar ----------
367 lewis:x:1001:1001:Bil Lewis,,,,:/home/lewis:/bin/bash
369 ---------- Buffer: bar ----------
373 Here is an example of the use of @code{call-process}, as used to
374 be found in the definition of the @code{insert-directory} function:
378 (call-process insert-directory-program nil t nil switches
380 (concat (file-name-as-directory file) ".")
386 @defun process-file program &optional infile buffer display &rest args
387 This function processes files synchronously in a separate process. It
388 is similar to @code{call-process}, but may invoke a file handler based
389 on the value of the variable @code{default-directory}, which specifies
390 the current working directory of the subprocess.
392 The arguments are handled in almost the same way as for
393 @code{call-process}, with the following differences:
395 Some file handlers may not support all combinations and forms of the
396 arguments @var{infile}, @var{buffer}, and @var{display}. For example,
397 some file handlers might behave as if @var{display} were @code{nil},
398 regardless of the value actually passed. As another example, some
399 file handlers might not support separating standard output and error
400 output by way of the @var{buffer} argument.
402 If a file handler is invoked, it determines the program to run based
403 on the first argument @var{program}. For instance, suppose that a
404 handler for remote files is invoked. Then the path that is used for
405 searching for the program might be different from @code{exec-path}.
407 The second argument @var{infile} may invoke a file handler. The file
408 handler could be different from the handler chosen for the
409 @code{process-file} function itself. (For example,
410 @code{default-directory} could be on one remote host, and
411 @var{infile} on a different remote host. Or @code{default-directory}
412 could be non-special, whereas @var{infile} is on a remote host.)
414 If @var{buffer} is a list of the form @code{(@var{real-destination}
415 @var{error-destination})}, and @var{error-destination} names a file,
416 then the same remarks as for @var{infile} apply.
418 The remaining arguments (@var{args}) will be passed to the process
419 verbatim. Emacs is not involved in processing file names that are
420 present in @var{args}. To avoid confusion, it may be best to avoid
421 absolute file names in @var{args}, but rather to specify all file
422 names as relative to @code{default-directory}. The function
423 @code{file-relative-name} is useful for constructing such relative
427 @defvar process-file-side-effects
428 This variable indicates whether a call of @code{process-file} changes
431 By default, this variable is always set to @code{t}, meaning that a
432 call of @code{process-file} could potentially change any file on a
433 remote host. When set to @code{nil}, a file handler could optimize
434 its behavior with respect to remote file attribute caching.
436 You should only ever change this variable with a let-binding; never
440 @defun call-process-region start end program &optional delete destination display &rest args
441 This function sends the text from @var{start} to @var{end} as
442 standard input to a process running @var{program}. It deletes the text
443 sent if @var{delete} is non-@code{nil}; this is useful when
444 @var{destination} is @code{t}, to insert the output in the current
445 buffer in place of the input.
447 The arguments @var{destination} and @var{display} control what to do
448 with the output from the subprocess, and whether to update the display
449 as it comes in. For details, see the description of
450 @code{call-process}, above. If @var{destination} is the integer 0,
451 @code{call-process-region} discards the output and returns @code{nil}
452 immediately, without waiting for the subprocess to finish (this only
453 works if asynchronous subprocesses are supported; i.e. not on MS-DOS).
455 The remaining arguments, @var{args}, are strings that specify command
456 line arguments for the program.
458 The return value of @code{call-process-region} is just like that of
459 @code{call-process}: @code{nil} if you told it to return without
460 waiting; otherwise, a number or string which indicates how the
461 subprocess terminated.
463 In the following example, we use @code{call-process-region} to run the
464 @code{cat} utility, with standard input being the first five characters
465 in buffer @samp{foo} (the word @samp{input}). @code{cat} copies its
466 standard input into its standard output. Since the argument
467 @var{destination} is @code{t}, this output is inserted in the current
472 ---------- Buffer: foo ----------
474 ---------- Buffer: foo ----------
478 (call-process-region 1 6 "cat" nil t)
481 ---------- Buffer: foo ----------
483 ---------- Buffer: foo ----------
487 For example, the @code{shell-command-on-region} command uses
488 @code{call-process-region} in a manner similar to this:
494 shell-file-name ; @r{name of program}
495 nil ; @r{do not delete region}
496 buffer ; @r{send output to @code{buffer}}
497 nil ; @r{no redisplay during output}
498 "-c" command) ; @r{arguments for the shell}
501 @c It actually uses shell-command-switch, but no need to mention that here.
504 @defun call-process-shell-command command &optional infile destination display &rest args
505 This function executes the shell command @var{command} synchronously.
506 The final arguments @var{args} are additional arguments to add at the
507 end of @var{command}. The other arguments are handled as in
511 @defun process-file-shell-command command &optional infile destination display &rest args
512 This function is like @code{call-process-shell-command}, but uses
513 @code{process-file} internally. Depending on @code{default-directory},
514 @var{command} can be executed also on remote hosts.
517 @defun shell-command-to-string command
518 This function executes @var{command} (a string) as a shell command,
519 then returns the command's output as a string.
522 @c There is also shell-command-on-region, but that is more of a user
523 @c command, not something to use in programs.
525 @defun process-lines program &rest args
526 This function runs @var{program}, waits for it to finish, and returns
527 its output as a list of strings. Each string in the list holds a
528 single line of text output by the program; the end-of-line characters
529 are stripped from each line. The arguments beyond @var{program},
530 @var{args}, are strings that specify command-line arguments with which
533 If @var{program} exits with a non-zero exit status, this function
536 This function works by calling @code{call-process}, so program output
537 is decoded in the same way as for @code{call-process}.
540 @node Asynchronous Processes
541 @section Creating an Asynchronous Process
542 @cindex asynchronous subprocess
544 After an @dfn{asynchronous process} is created, Emacs and the subprocess
545 both continue running immediately. The process thereafter runs
546 in parallel with Emacs, and the two can communicate with each other
547 using the functions described in the following sections. However,
548 communication is only partially asynchronous: Emacs sends data to the
549 process only when certain functions are called, and Emacs accepts data
550 from the process only when Emacs is waiting for input or for a time
553 Here we describe how to create an asynchronous process.
555 @defun start-process name buffer-or-name program &rest args
556 This function creates a new asynchronous subprocess and starts the
557 program @var{program} running in it. It returns a process object that
558 stands for the new subprocess in Lisp. The argument @var{name}
559 specifies the name for the process object; if a process with this name
560 already exists, then @var{name} is modified (by appending @samp{<1>},
561 etc.) to be unique. The buffer @var{buffer-or-name} is the buffer to
562 associate with the process.
564 The remaining arguments, @var{args}, are strings that specify command
565 line arguments for the program.
567 In the example below, the first process is started and runs (rather,
568 sleeps) for 100 seconds (the output buffer @samp{foo} is created
569 immediately). Meanwhile, the second process is started, and
570 given the name @samp{my-process<1>} for the sake of uniqueness. It
571 inserts the directory listing at the end of the buffer @samp{foo},
572 before the first process finishes. Then it finishes, and a message to
573 that effect is inserted in the buffer. Much later, the first process
574 finishes, and another message is inserted in the buffer for it.
578 (start-process "my-process" "foo" "sleep" "100")
579 @result{} #<process my-process>
583 (start-process "my-process" "foo" "ls" "-l" "/bin")
584 @result{} #<process my-process<1>>
586 ---------- Buffer: foo ----------
588 -rwxr-xr-x 1 root root 971384 Mar 30 10:14 bash
589 -rwxr-xr-x 1 root root 146920 Jul 5 2011 bsd-csh
591 -rwxr-xr-x 1 root root 696880 Feb 28 15:55 zsh4
593 Process my-process<1> finished
595 Process my-process finished
596 ---------- Buffer: foo ----------
601 @defun start-file-process name buffer-or-name program &rest args
602 Like @code{start-process}, this function starts a new asynchronous
603 subprocess running @var{program} in it, and returns its process
606 The difference from @code{start-process} is that this function may
607 invoked a file handler based on the value of @code{default-directory}.
608 This handler ought to run @var{program}, perhaps on the local host,
609 perhaps on a remote host that corresponds to @code{default-directory}.
610 In the latter case, the local part of @code{default-directory} becomes
611 the working directory of the process.
613 This function does not try to invoke file name handlers for
614 @var{program} or for the @var{program-args}.
616 Depending on the implementation of the file handler, it might not be
617 possible to apply @code{process-filter} or @code{process-sentinel} to
618 the resulting process object. @xref{Filter Functions}, and @ref{Sentinels}.
620 @c FIXME Can we find a better example (i.e. a more modern function
621 @c that is actually documented).
622 Some file handlers may not support @code{start-file-process} (for
623 example the function @code{ange-ftp-hook-function}). In such cases,
624 this function does nothing and returns @code{nil}.
627 @defun start-process-shell-command name buffer-or-name command
628 This function is like @code{start-process}, except that it uses a shell
629 to execute the specified command. The argument @var{command} is a shell
630 command name. The variable @code{shell-file-name} specifies which shell to
633 The point of running a program through the shell, rather than directly
634 with @code{start-process}, is so that you can employ shell features such
635 as wildcards in the arguments. It follows that if you include any
636 arbitrary user-specified arguments in the command, you should quote them
637 with @code{shell-quote-argument} first, so that any special shell
638 characters do @emph{not} have their special shell meanings. @xref{Shell
639 Arguments}. Of course, when executing commands based on user input
640 you should also consider the security implications.
643 @defun start-file-process-shell-command name buffer-or-name command
644 This function is like @code{start-process-shell-command}, but uses
645 @code{start-file-process} internally. Because of this, @var{command}
646 can also be executed on remote hosts, depending on @code{default-directory}.
649 @defvar process-connection-type
651 @cindex @acronym{PTY}s
652 This variable controls the type of device used to communicate with
653 asynchronous subprocesses. If it is non-@code{nil}, then @acronym{PTY}s are
654 used, when available. Otherwise, pipes are used.
656 @acronym{PTY}s are usually preferable for processes visible to the user, as
657 in Shell mode, because they allow job control (@kbd{C-c}, @kbd{C-z},
658 etc.) to work between the process and its children, whereas pipes do
659 not. For subprocesses used for internal purposes by programs, it is
660 often better to use a pipe, because they are more efficient. In
661 addition, the total number of @acronym{PTY}s is limited on many systems and
662 it is good not to waste them.
664 The value of @code{process-connection-type} takes effect when
665 @code{start-process} is called. So you can specify how to communicate
666 with one subprocess by binding the variable around the call to
667 @code{start-process}.
671 (let ((process-connection-type nil)) ; @r{use a pipe}
672 (start-process @dots{}))
676 To determine whether a given subprocess actually got a pipe or a
677 @acronym{PTY}, use the function @code{process-tty-name} (@pxref{Process
681 @node Deleting Processes
682 @section Deleting Processes
683 @cindex deleting processes
685 @dfn{Deleting a process} disconnects Emacs immediately from the
686 subprocess. Processes are deleted automatically after they terminate,
687 but not necessarily right away. You can delete a process explicitly
688 at any time. If you explicitly delete a terminated process before it
689 is deleted automatically, no harm results. Deleting a running
690 process sends a signal to terminate it (and its child processes, if
691 any), and calls the process sentinel if it has one. @xref{Sentinels}.
693 When a process is deleted, the process object itself continues to
694 exist as long as other Lisp objects point to it. All the Lisp
695 primitives that work on process objects accept deleted processes, but
696 those that do I/O or send signals will report an error. The process
697 mark continues to point to the same place as before, usually into a
698 buffer where output from the process was being inserted.
700 @defopt delete-exited-processes
701 This variable controls automatic deletion of processes that have
702 terminated (due to calling @code{exit} or to a signal). If it is
703 @code{nil}, then they continue to exist until the user runs
704 @code{list-processes}. Otherwise, they are deleted immediately after
708 @defun delete-process process
709 This function deletes a process, killing it with a @code{SIGKILL}
710 signal. The argument may be a process, the name of a process, a
711 buffer, or the name of a buffer. (A buffer or buffer-name stands for
712 the process that @code{get-buffer-process} returns.) Calling
713 @code{delete-process} on a running process terminates it, updates the
714 process status, and runs the sentinel (if any) immediately. If the
715 process has already terminated, calling @code{delete-process} has no
716 effect on its status, or on the running of its sentinel (which will
717 happen sooner or later).
721 (delete-process "*shell*")
727 @node Process Information
728 @section Process Information
730 Several functions return information about processes.
731 @code{list-processes} is provided for interactive use.
733 @deffn Command list-processes &optional query-only
734 This command displays a listing of all living processes. In addition,
735 it finally deletes any process whose status was @samp{Exited} or
736 @samp{Signaled}. It returns @code{nil}.
738 The processes are shown in a buffer named @file{*Process List*}, whose
739 major mode is named Process Menu mode.
741 If @var{query-only} is non-@code{nil} then it lists only processes
742 whose query flag is non-@code{nil}. @xref{Query Before Exit}.
746 This function returns a list of all processes that have not been deleted.
751 @result{} (#<process display-time> #<process shell>)
756 @defun get-process name
757 This function returns the process named @var{name}, or @code{nil} if
758 there is none. An error is signaled if @var{name} is not a string.
762 (get-process "shell")
763 @result{} #<process shell>
768 @defun process-command process
769 This function returns the command that was executed to start
770 @var{process}. This is a list of strings, the first string being the
771 program executed and the rest of the strings being the arguments that
772 were given to the program.
776 (process-command (get-process "shell"))
777 @result{} ("/bin/csh" "-i")
782 @defun process-contact process &optional key
784 This function returns information about how a network or serial
785 process was set up. For a network process, when @var{key} is
786 @code{nil}, it returns @code{(@var{hostname} @var{service})} which
787 specifies what you connected to. For a serial process, when @var{key}
788 is @code{nil}, it returns @code{(@var{port} @var{speed})}. For an
789 ordinary child process, this function always returns @code{t}.
791 If @var{key} is @code{t}, the value is the complete status information
792 for the connection, server, or serial port; that is, the list of
793 keywords and values specified in @code{make-network-process} or
794 @code{make-serial-process}, except that some of the values represent
795 the current status instead of what you specified.
797 For a network process:
801 The associated value is the process buffer.
803 The associated value is the process filter function.
805 The associated value is the process sentinel function.
807 In a connection, the address in internal format of the remote peer.
809 The local address, in internal format.
811 In a server, if you specified @code{t} for @var{service},
812 this value is the actual port number.
815 @code{:local} and @code{:remote} are included even if they were not
816 specified explicitly in @code{make-network-process}.
818 For a serial process, see @code{make-serial-process} and
819 @code{serial-process-configure} for a list of keys.
821 If @var{key} is a keyword, the function returns the value corresponding
825 @defun process-id process
826 This function returns the @acronym{PID} of @var{process}. This is an
827 integer that distinguishes the process @var{process} from all other
828 processes running on the same computer at the current time. The
829 @acronym{PID} of a process is chosen by the operating system kernel when the
830 process is started and remains constant as long as the process exists.
833 @defun process-name process
834 This function returns the name of @var{process}.
837 @defun process-status process-name
838 This function returns the status of @var{process-name} as a symbol.
839 The argument @var{process-name} must be a process, a buffer, or a
840 process name (a string).
842 The possible values for an actual subprocess are:
846 for a process that is running.
848 for a process that is stopped but continuable.
850 for a process that has exited.
852 for a process that has received a fatal signal.
854 for a network connection that is open.
856 for a network connection that is closed. Once a connection
857 is closed, you cannot reopen it, though you might be able to open
858 a new connection to the same place.
860 for a non-blocking connection that is waiting to complete.
862 for a non-blocking connection that has failed to complete.
864 for a network server that is listening.
866 if @var{process-name} is not the name of an existing process.
871 (process-status (get-buffer "*shell*"))
876 @result{} #<process xx<1>>
882 For a network connection, @code{process-status} returns one of the symbols
883 @code{open} or @code{closed}. The latter means that the other side
884 closed the connection, or Emacs did @code{delete-process}.
887 @defun process-live-p process
888 This function returns non-@code{nil} if @var{process} is alive. A
889 process is considered alive if its status is @code{run}, @code{open},
890 @code{listen}, @code{connect} or @code{stop}.
893 @defun process-type process
894 This function returns the symbol @code{network} for a network
895 connection or server, @code{serial} for a serial port connection, or
896 @code{real} for a real subprocess.
899 @defun process-exit-status process
900 This function returns the exit status of @var{process} or the signal
901 number that killed it. (Use the result of @code{process-status} to
902 determine which of those it is.) If @var{process} has not yet
903 terminated, the value is 0.
906 @defun process-tty-name process
907 This function returns the terminal name that @var{process} is using for
908 its communication with Emacs---or @code{nil} if it is using pipes
909 instead of a terminal (see @code{process-connection-type} in
910 @ref{Asynchronous Processes}). If @var{process} represents a program
911 running on a remote host, the terminal name used by that program on
912 the remote host is provided as process property @code{remote-tty}.
915 @defun process-coding-system process
916 @anchor{Coding systems for a subprocess}
917 This function returns a cons cell describing the coding systems in use
918 for decoding output from @var{process} and for encoding input to
919 @var{process} (@pxref{Coding Systems}). The value has this form:
922 (@var{coding-system-for-decoding} . @var{coding-system-for-encoding})
926 @defun set-process-coding-system process &optional decoding-system encoding-system
927 This function specifies the coding systems to use for subsequent output
928 from and input to @var{process}. It will use @var{decoding-system} to
929 decode subprocess output, and @var{encoding-system} to encode subprocess
933 Every process also has a property list that you can use to store
934 miscellaneous values associated with the process.
936 @defun process-get process propname
937 This function returns the value of the @var{propname} property
941 @defun process-put process propname value
942 This function sets the value of the @var{propname} property
943 of @var{process} to @var{value}.
946 @defun process-plist process
947 This function returns the process plist of @var{process}.
950 @defun set-process-plist process plist
951 This function sets the process plist of @var{process} to @var{plist}.
954 @node Input to Processes
955 @section Sending Input to Processes
956 @cindex process input
958 Asynchronous subprocesses receive input when it is sent to them by
959 Emacs, which is done with the functions in this section. You must
960 specify the process to send input to, and the input data to send. The
961 data appears on the ``standard input'' of the subprocess.
963 Some operating systems have limited space for buffered input in a
964 @acronym{PTY}. On these systems, Emacs sends an @acronym{EOF}
965 periodically amidst the other characters, to force them through. For
966 most programs, these @acronym{EOF}s do no harm.
968 Subprocess input is normally encoded using a coding system before the
969 subprocess receives it, much like text written into a file. You can use
970 @code{set-process-coding-system} to specify which coding system to use
971 (@pxref{Process Information}). Otherwise, the coding system comes from
972 @code{coding-system-for-write}, if that is non-@code{nil}; or else from
973 the defaulting mechanism (@pxref{Default Coding Systems}).
975 Sometimes the system is unable to accept input for that process,
976 because the input buffer is full. When this happens, the send functions
977 wait a short while, accepting output from subprocesses, and then try
978 again. This gives the subprocess a chance to read more of its pending
979 input and make space in the buffer. It also allows filters, sentinels
980 and timers to run---so take account of that in writing your code.
982 In these functions, the @var{process} argument can be a process or
983 the name of a process, or a buffer or buffer name (which stands
984 for a process via @code{get-buffer-process}). @code{nil} means
985 the current buffer's process.
987 @defun process-send-string process string
988 This function sends @var{process} the contents of @var{string} as
989 standard input. If it is @code{nil}, the current buffer's process is used.
991 The function returns @code{nil}.
995 (process-send-string "shell<1>" "ls\n")
1001 ---------- Buffer: *shell* ----------
1003 introduction.texi syntax-tables.texi~
1004 introduction.texi~ text.texi
1005 introduction.txt text.texi~
1007 ---------- Buffer: *shell* ----------
1012 @defun process-send-region process start end
1013 This function sends the text in the region defined by @var{start} and
1014 @var{end} as standard input to @var{process}.
1016 An error is signaled unless both @var{start} and @var{end} are
1017 integers or markers that indicate positions in the current buffer. (It
1018 is unimportant which number is larger.)
1021 @defun process-send-eof &optional process
1022 This function makes @var{process} see an end-of-file in its
1023 input. The @acronym{EOF} comes after any text already sent to it.
1025 The function returns @var{process}.
1029 (process-send-eof "shell")
1035 @defun process-running-child-p &optional process
1036 This function will tell you whether a @var{process} has given control of
1037 its terminal to its own child process. The value is @code{t} if this is
1038 true, or if Emacs cannot tell; it is @code{nil} if Emacs can be certain
1039 that this is not so.
1042 @node Signals to Processes
1043 @section Sending Signals to Processes
1044 @cindex process signals
1045 @cindex sending signals
1048 @dfn{Sending a signal} to a subprocess is a way of interrupting its
1049 activities. There are several different signals, each with its own
1050 meaning. The set of signals and their names is defined by the operating
1051 system. For example, the signal @code{SIGINT} means that the user has
1052 typed @kbd{C-c}, or that some analogous thing has happened.
1054 Each signal has a standard effect on the subprocess. Most signals
1055 kill the subprocess, but some stop or resume execution instead. Most
1056 signals can optionally be handled by programs; if the program handles
1057 the signal, then we can say nothing in general about its effects.
1059 You can send signals explicitly by calling the functions in this
1060 section. Emacs also sends signals automatically at certain times:
1061 killing a buffer sends a @code{SIGHUP} signal to all its associated
1062 processes; killing Emacs sends a @code{SIGHUP} signal to all remaining
1063 processes. (@code{SIGHUP} is a signal that usually indicates that the
1064 user hung up the phone.)
1066 Each of the signal-sending functions takes two optional arguments:
1067 @var{process} and @var{current-group}.
1069 The argument @var{process} must be either a process, a process
1070 name, a buffer, a buffer name, or @code{nil}. A buffer or buffer name
1071 stands for a process through @code{get-buffer-process}. @code{nil}
1072 stands for the process associated with the current buffer. An error
1073 is signaled if @var{process} does not identify a process.
1075 The argument @var{current-group} is a flag that makes a difference
1076 when you are running a job-control shell as an Emacs subprocess. If it
1077 is non-@code{nil}, then the signal is sent to the current process-group
1078 of the terminal that Emacs uses to communicate with the subprocess. If
1079 the process is a job-control shell, this means the shell's current
1080 subjob. If it is @code{nil}, the signal is sent to the process group of
1081 the immediate subprocess of Emacs. If the subprocess is a job-control
1082 shell, this is the shell itself.
1084 The flag @var{current-group} has no effect when a pipe is used to
1085 communicate with the subprocess, because the operating system does not
1086 support the distinction in the case of pipes. For the same reason,
1087 job-control shells won't work when a pipe is used. See
1088 @code{process-connection-type} in @ref{Asynchronous Processes}.
1090 @defun interrupt-process &optional process current-group
1091 This function interrupts the process @var{process} by sending the
1092 signal @code{SIGINT}. Outside of Emacs, typing the ``interrupt
1093 character'' (normally @kbd{C-c} on some systems, and @code{DEL} on
1094 others) sends this signal. When the argument @var{current-group} is
1095 non-@code{nil}, you can think of this function as ``typing @kbd{C-c}''
1096 on the terminal by which Emacs talks to the subprocess.
1099 @defun kill-process &optional process current-group
1100 This function kills the process @var{process} by sending the
1101 signal @code{SIGKILL}. This signal kills the subprocess immediately,
1102 and cannot be handled by the subprocess.
1105 @defun quit-process &optional process current-group
1106 This function sends the signal @code{SIGQUIT} to the process
1107 @var{process}. This signal is the one sent by the ``quit
1108 character'' (usually @kbd{C-b} or @kbd{C-\}) when you are not inside
1112 @defun stop-process &optional process current-group
1113 This function stops the process @var{process} by sending the
1114 signal @code{SIGTSTP}. Use @code{continue-process} to resume its
1117 Outside of Emacs, on systems with job control, the ``stop character''
1118 (usually @kbd{C-z}) normally sends this signal. When
1119 @var{current-group} is non-@code{nil}, you can think of this function as
1120 ``typing @kbd{C-z}'' on the terminal Emacs uses to communicate with the
1124 @defun continue-process &optional process current-group
1125 This function resumes execution of the process @var{process} by sending
1126 it the signal @code{SIGCONT}. This presumes that @var{process} was
1130 @defun signal-process process signal
1131 This function sends a signal to process @var{process}. The argument
1132 @var{signal} specifies which signal to send; it should be an integer.
1134 The @var{process} argument can be a system process @acronym{ID}; that
1135 allows you to send signals to processes that are not children of
1136 Emacs. @xref{System Processes}.
1139 @node Output from Processes
1140 @section Receiving Output from Processes
1141 @cindex process output
1142 @cindex output from processes
1144 There are two ways to receive the output that a subprocess writes to
1145 its standard output stream. The output can be inserted in a buffer,
1146 which is called the associated buffer of the process, or a function
1147 called the @dfn{filter function} can be called to act on the output. If
1148 the process has no buffer and no filter function, its output is
1151 When a subprocess terminates, Emacs reads any pending output,
1152 then stops reading output from that subprocess. Therefore, if the
1153 subprocess has children that are still live and still producing
1154 output, Emacs won't receive that output.
1156 Output from a subprocess can arrive only while Emacs is waiting: when
1157 reading terminal input, in @code{sit-for} and @code{sleep-for}
1158 (@pxref{Waiting}), and in @code{accept-process-output} (@pxref{Accepting
1159 Output}). This minimizes the problem of timing errors that usually
1160 plague parallel programming. For example, you can safely create a
1161 process and only then specify its buffer or filter function; no output
1162 can arrive before you finish, if the code in between does not call any
1163 primitive that waits.
1165 @defvar process-adaptive-read-buffering
1166 On some systems, when Emacs reads the output from a subprocess, the
1167 output data is read in very small blocks, potentially resulting in
1168 very poor performance. This behavior can be remedied to some extent
1169 by setting the variable @var{process-adaptive-read-buffering} to a
1170 non-@code{nil} value (the default), as it will automatically delay reading
1171 from such processes, thus allowing them to produce more output before
1172 Emacs tries to read it.
1175 It is impossible to separate the standard output and standard error
1176 streams of the subprocess, because Emacs normally spawns the subprocess
1177 inside a pseudo-TTY, and a pseudo-TTY has only one output channel. If
1178 you want to keep the output to those streams separate, you should
1179 redirect one of them to a file---for example, by using an appropriate
1183 * Process Buffers:: If no filter, output is put in a buffer.
1184 * Filter Functions:: Filter functions accept output from the process.
1185 * Decoding Output:: Filters can get unibyte or multibyte strings.
1186 * Accepting Output:: How to wait until process output arrives.
1189 @node Process Buffers
1190 @subsection Process Buffers
1192 A process can (and usually does) have an @dfn{associated buffer},
1193 which is an ordinary Emacs buffer that is used for two purposes: storing
1194 the output from the process, and deciding when to kill the process. You
1195 can also use the buffer to identify a process to operate on, since in
1196 normal practice only one process is associated with any given buffer.
1197 Many applications of processes also use the buffer for editing input to
1198 be sent to the process, but this is not built into Emacs Lisp.
1200 Unless the process has a filter function (@pxref{Filter Functions}),
1201 its output is inserted in the associated buffer. The position to insert
1202 the output is determined by the @code{process-mark}, which is then
1203 updated to point to the end of the text just inserted. Usually, but not
1204 always, the @code{process-mark} is at the end of the buffer.
1206 @findex process-kill-buffer-query-function
1207 Killing the associated buffer of a process also kills the process.
1208 Emacs asks for confirmation first, if the process's
1209 @code{process-query-on-exit-flag} is non-@code{nil} (@pxref{Query
1210 Before Exit}). This confirmation is done by the function
1211 @code{process-kill-buffer-query-function}, which is run from
1212 @code{kill-buffer-query-functions} (@pxref{Killing Buffers}).
1214 @defun process-buffer process
1215 This function returns the associated buffer of the process
1220 (process-buffer (get-process "shell"))
1221 @result{} #<buffer *shell*>
1226 @defun process-mark process
1227 This function returns the process marker for @var{process}, which is the
1228 marker that says where to insert output from the process.
1230 If @var{process} does not have a buffer, @code{process-mark} returns a
1231 marker that points nowhere.
1233 Insertion of process output in a buffer uses this marker to decide where
1234 to insert, and updates it to point after the inserted text. That is why
1235 successive batches of output are inserted consecutively.
1237 Filter functions normally should use this marker in the same fashion
1238 as is done by direct insertion of output in the buffer. A good
1239 example of a filter function that uses @code{process-mark} is found at
1240 the end of the following section.
1242 When the user is expected to enter input in the process buffer for
1243 transmission to the process, the process marker separates the new input
1244 from previous output.
1247 @defun set-process-buffer process buffer
1248 This function sets the buffer associated with @var{process} to
1249 @var{buffer}. If @var{buffer} is @code{nil}, the process becomes
1250 associated with no buffer.
1253 @defun get-buffer-process buffer-or-name
1254 This function returns a nondeleted process associated with the buffer
1255 specified by @var{buffer-or-name}. If there are several processes
1256 associated with it, this function chooses one (currently, the one most
1257 recently created, but don't count on that). Deletion of a process
1258 (see @code{delete-process}) makes it ineligible for this function to
1261 It is usually a bad idea to have more than one process associated with
1266 (get-buffer-process "*shell*")
1267 @result{} #<process shell>
1271 Killing the process's buffer deletes the process, which kills the
1272 subprocess with a @code{SIGHUP} signal (@pxref{Signals to Processes}).
1275 @node Filter Functions
1276 @subsection Process Filter Functions
1277 @cindex filter function
1278 @cindex process filter
1280 A process @dfn{filter function} is a function that receives the
1281 standard output from the associated process. If a process has a filter,
1282 then @emph{all} output from that process is passed to the filter. The
1283 process buffer is used directly for output from the process only when
1286 The filter function can only be called when Emacs is waiting for
1287 something, because process output arrives only at such times. Emacs
1288 waits when reading terminal input, in @code{sit-for} and
1289 @code{sleep-for} (@pxref{Waiting}), and in @code{accept-process-output}
1290 (@pxref{Accepting Output}).
1292 A filter function must accept two arguments: the associated process
1293 and a string, which is output just received from it. The function is
1294 then free to do whatever it chooses with the output.
1296 Quitting is normally inhibited within a filter function---otherwise,
1297 the effect of typing @kbd{C-g} at command level or to quit a user
1298 command would be unpredictable. If you want to permit quitting inside
1299 a filter function, bind @code{inhibit-quit} to @code{nil}. In most
1300 cases, the right way to do this is with the macro
1301 @code{with-local-quit}. @xref{Quitting}.
1303 If an error happens during execution of a filter function, it is
1304 caught automatically, so that it doesn't stop the execution of whatever
1305 program was running when the filter function was started. However, if
1306 @code{debug-on-error} is non-@code{nil}, the error-catching is turned
1307 off. This makes it possible to use the Lisp debugger to debug the
1308 filter function. @xref{Debugger}.
1310 Many filter functions sometimes or always insert the text in the
1311 process's buffer, mimicking the actions of Emacs when there is no
1312 filter. Such filter functions need to use @code{set-buffer} in order to
1313 be sure to insert in that buffer. To avoid setting the current buffer
1314 semipermanently, these filter functions must save and restore the
1315 current buffer. They should also check whether the buffer is still
1316 alive, update the process marker, and in some cases update the value
1317 of point. Here is how to do these things:
1321 (defun ordinary-insertion-filter (proc string)
1322 (when (buffer-live-p (process-buffer proc))
1323 (with-current-buffer (process-buffer proc)
1324 (let ((moving (= (point) (process-mark proc))))
1328 ;; @r{Insert the text, advancing the process marker.}
1329 (goto-char (process-mark proc))
1331 (set-marker (process-mark proc) (point)))
1332 (if moving (goto-char (process-mark proc)))))))
1337 The reason to use @code{with-current-buffer}, rather than using
1338 @code{save-excursion} to save and restore the current buffer, is so as
1339 to preserve the change in point made by the second call to
1342 To make the filter force the process buffer to be visible whenever new
1343 text arrives, insert the following line just before the
1344 @code{with-current-buffer} construct:
1347 (display-buffer (process-buffer proc))
1350 To force point to the end of the new output, no matter where it was
1351 previously, eliminate the variable @code{moving} and call
1352 @code{goto-char} unconditionally.
1354 In earlier Emacs versions, every filter function that did regular
1355 expression searching or matching had to explicitly save and restore the
1356 match data. Now Emacs does this automatically for filter functions;
1357 they never need to do it explicitly. @xref{Match Data}.
1359 The output to the function may come in chunks of any size. A program
1360 that produces the same output twice in a row may send it as one batch of
1361 200 characters one time, and five batches of 40 characters the next. If
1362 the filter looks for certain text strings in the subprocess output, make
1363 sure to handle the case where one of these strings is split across two
1364 or more batches of output; one way to do this is to insert the
1365 received text into a temporary buffer, which can then be searched.
1367 @defun set-process-filter process filter
1368 This function gives @var{process} the filter function @var{filter}. If
1369 @var{filter} is @code{nil}, it gives the process no filter.
1372 @defun process-filter process
1373 This function returns the filter function of @var{process}, or @code{nil}
1377 Here is an example of use of a filter function:
1381 (defun keep-output (process output)
1382 (setq kept (cons output kept)))
1383 @result{} keep-output
1390 (set-process-filter (get-process "shell") 'keep-output)
1391 @result{} keep-output
1394 (process-send-string "shell" "ls ~/other\n")
1397 @result{} ("lewis@@slug[8] % "
1400 "FINAL-W87-SHORT.MSS backup.otl kolstad.mss~
1401 address.txt backup.psf kolstad.psf
1402 backup.bib~ david.mss resume-Dec-86.mss~
1403 backup.err david.psf resume-Dec.psf
1404 backup.mss dland syllabus.mss
1406 "#backups.mss# backup.mss~ kolstad.mss
1411 @ignore @c The code in this example doesn't show the right way to do things.
1412 Here is another, more realistic example, which demonstrates how to use
1413 the process mark to do insertion in the same fashion as is done when
1414 there is no filter function:
1418 ;; @r{Insert input in the buffer specified by @code{my-shell-buffer}}
1419 ;; @r{and make sure that buffer is shown in some window.}
1420 (defun my-process-filter (proc str)
1421 (let ((cur (selected-window))
1423 (pop-to-buffer my-shell-buffer)
1426 (goto-char (point-max))
1428 (set-marker (process-mark proc) (point-max))
1429 (select-window cur)))
1434 @node Decoding Output
1435 @subsection Decoding Process Output
1436 @cindex decode process output
1438 When Emacs writes process output directly into a multibyte buffer,
1439 it decodes the output according to the process output coding system.
1440 If the coding system is @code{raw-text} or @code{no-conversion}, Emacs
1441 converts the unibyte output to multibyte using
1442 @code{string-to-multibyte}, and inserts the resulting multibyte text.
1444 You can use @code{set-process-coding-system} to specify which coding
1445 system to use (@pxref{Process Information}). Otherwise, the coding
1446 system comes from @code{coding-system-for-read}, if that is
1447 non-@code{nil}; or else from the defaulting mechanism (@pxref{Default
1448 Coding Systems}). If the text output by a process contains null
1449 bytes, Emacs by default uses @code{no-conversion} for it; see
1450 @ref{Lisp and Coding Systems, inhibit-null-byte-detection}, for how to
1451 control this behavior.
1453 @strong{Warning:} Coding systems such as @code{undecided} which
1454 determine the coding system from the data do not work entirely
1455 reliably with asynchronous subprocess output. This is because Emacs
1456 has to process asynchronous subprocess output in batches, as it
1457 arrives. Emacs must try to detect the proper coding system from one
1458 batch at a time, and this does not always work. Therefore, if at all
1459 possible, specify a coding system that determines both the character
1460 code conversion and the end of line conversion---that is, one like
1461 @code{latin-1-unix}, rather than @code{undecided} or @code{latin-1}.
1463 @c Let's keep the index entries that were there for
1464 @c set-process-filter-multibyte and process-filter-multibyte-p,
1465 @cindex filter multibyte flag, of process
1466 @cindex process filter multibyte flag
1467 When Emacs calls a process filter function, it provides the process
1468 output as a multibyte string or as a unibyte string according to the
1469 process's filter coding system. Emacs
1470 decodes the output according to the process output coding system,
1471 which usually produces a multibyte string, except for coding systems
1472 such as @code{binary} and @code{raw-text}
1474 @node Accepting Output
1475 @subsection Accepting Output from Processes
1476 @cindex accept input from processes
1478 Output from asynchronous subprocesses normally arrives only while
1479 Emacs is waiting for some sort of external event, such as elapsed time
1480 or terminal input. Occasionally it is useful in a Lisp program to
1481 explicitly permit output to arrive at a specific point, or even to wait
1482 until output arrives from a process.
1484 @defun accept-process-output &optional process seconds millisec just-this-one
1485 This function allows Emacs to read pending output from processes. The
1486 output is inserted in the associated buffers or given to their filter
1487 functions. If @var{process} is non-@code{nil} then this function does
1488 not return until some output has been received from @var{process}.
1491 The arguments @var{seconds} and @var{millisec} let you specify timeout
1492 periods. The former specifies a period measured in seconds and the
1493 latter specifies one measured in milliseconds. The two time periods
1494 thus specified are added together, and @code{accept-process-output}
1495 returns after that much time, whether or not there has been any
1498 The argument @var{millisec} is semi-obsolete nowadays because
1499 @var{seconds} can be a floating point number to specify waiting a
1500 fractional number of seconds. If @var{seconds} is 0, the function
1501 accepts whatever output is pending but does not wait.
1503 @c Emacs 22.1 feature
1504 If @var{process} is a process, and the argument @var{just-this-one} is
1505 non-@code{nil}, only output from that process is handled, suspending output
1506 from other processes until some output has been received from that
1507 process or the timeout expires. If @var{just-this-one} is an integer,
1508 also inhibit running timers. This feature is generally not
1509 recommended, but may be necessary for specific applications, such as
1512 The function @code{accept-process-output} returns non-@code{nil} if it
1513 did get some output, or @code{nil} if the timeout expired before output
1518 @section Sentinels: Detecting Process Status Changes
1519 @cindex process sentinel
1520 @cindex sentinel (of process)
1522 A @dfn{process sentinel} is a function that is called whenever the
1523 associated process changes status for any reason, including signals
1524 (whether sent by Emacs or caused by the process's own actions) that
1525 terminate, stop, or continue the process. The process sentinel is
1526 also called if the process exits. The sentinel receives two
1527 arguments: the process for which the event occurred, and a string
1528 describing the type of event.
1530 The string describing the event looks like one of the following:
1534 @code{"finished\n"}.
1537 @code{"exited abnormally with code @var{exitcode}\n"}.
1540 @code{"@var{name-of-signal}\n"}.
1543 @code{"@var{name-of-signal} (core dumped)\n"}.
1546 A sentinel runs only while Emacs is waiting (e.g., for terminal
1547 input, or for time to elapse, or for process output). This avoids the
1548 timing errors that could result from running them at random places in
1549 the middle of other Lisp programs. A program can wait, so that
1550 sentinels will run, by calling @code{sit-for} or @code{sleep-for}
1551 (@pxref{Waiting}), or @code{accept-process-output} (@pxref{Accepting
1552 Output}). Emacs also allows sentinels to run when the command loop is
1553 reading input. @code{delete-process} calls the sentinel when it
1554 terminates a running process.
1556 Emacs does not keep a queue of multiple reasons to call the sentinel
1557 of one process; it records just the current status and the fact that
1558 there has been a change. Therefore two changes in status, coming in
1559 quick succession, can call the sentinel just once. However, process
1560 termination will always run the sentinel exactly once. This is
1561 because the process status can't change again after termination.
1563 Emacs explicitly checks for output from the process before running
1564 the process sentinel. Once the sentinel runs due to process
1565 termination, no further output can arrive from the process.
1567 A sentinel that writes the output into the buffer of the process
1568 should check whether the buffer is still alive. If it tries to insert
1569 into a dead buffer, it will get an error. If the buffer is dead,
1570 @code{(buffer-name (process-buffer @var{process}))} returns @code{nil}.
1572 Quitting is normally inhibited within a sentinel---otherwise, the
1573 effect of typing @kbd{C-g} at command level or to quit a user command
1574 would be unpredictable. If you want to permit quitting inside a
1575 sentinel, bind @code{inhibit-quit} to @code{nil}. In most cases, the
1576 right way to do this is with the macro @code{with-local-quit}.
1579 If an error happens during execution of a sentinel, it is caught
1580 automatically, so that it doesn't stop the execution of whatever
1581 programs was running when the sentinel was started. However, if
1582 @code{debug-on-error} is non-@code{nil}, the error-catching is turned
1583 off. This makes it possible to use the Lisp debugger to debug the
1584 sentinel. @xref{Debugger}.
1586 While a sentinel is running, the process sentinel is temporarily
1587 set to @code{nil} so that the sentinel won't run recursively.
1588 For this reason it is not possible for a sentinel to specify
1591 In earlier Emacs versions, every sentinel that did regular expression
1592 searching or matching had to explicitly save and restore the match data.
1593 Now Emacs does this automatically for sentinels; they never need to do
1594 it explicitly. @xref{Match Data}.
1596 @defun set-process-sentinel process sentinel
1597 This function associates @var{sentinel} with @var{process}. If
1598 @var{sentinel} is @code{nil}, then the process will have no sentinel.
1599 The default behavior when there is no sentinel is to insert a message in
1600 the process's buffer when the process status changes.
1602 Changes in process sentinel take effect immediately---if the sentinel
1603 is slated to be run but has not been called yet, and you specify a new
1604 sentinel, the eventual call to the sentinel will use the new one.
1608 (defun msg-me (process event)
1610 (format "Process: %s had the event `%s'" process event)))
1611 (set-process-sentinel (get-process "shell") 'msg-me)
1615 (kill-process (get-process "shell"))
1616 @print{} Process: #<process shell> had the event `killed'
1617 @result{} #<process shell>
1622 @defun process-sentinel process
1623 This function returns the sentinel of @var{process}, or @code{nil} if it
1627 @defun waiting-for-user-input-p
1628 While a sentinel or filter function is running, this function returns
1629 non-@code{nil} if Emacs was waiting for keyboard input from the user at
1630 the time the sentinel or filter function was called, @code{nil} if it
1634 @node Query Before Exit
1635 @section Querying Before Exit
1637 When Emacs exits, it terminates all its subprocesses by sending them
1638 the @code{SIGHUP} signal. Because subprocesses may be doing
1639 valuable work, Emacs normally asks the user to confirm that it is ok
1640 to terminate them. Each process has a query flag which, if
1641 non-@code{nil}, says that Emacs should ask for confirmation before
1642 exiting and thus killing that process. The default for the query flag
1643 is @code{t}, meaning @emph{do} query.
1645 @defun process-query-on-exit-flag process
1646 This returns the query flag of @var{process}.
1649 @defun set-process-query-on-exit-flag process flag
1650 This function sets the query flag of @var{process} to @var{flag}. It
1653 Here is an example of using @code{set-process-query-on-exit-flag} on a
1654 shell process to avoid querying:
1658 (set-process-query-on-exit-flag (get-process "shell") nil)
1664 @node System Processes
1665 @section Accessing Other Processes
1666 @cindex system processes
1668 In addition to accessing and manipulating processes that are
1669 subprocesses of the current Emacs session, Emacs Lisp programs can
1670 also access other processes running on the same machine. We call
1671 these @dfn{system processes}, to distinguish between them and Emacs
1674 Emacs provides several primitives for accessing system processes.
1675 Not all platforms support these primitives; on those which don't,
1676 these primitives return @code{nil}.
1678 @defun list-system-processes
1679 This function returns a list of all the processes running on the
1680 system. Each process is identified by its @acronym{PID}, a numerical
1681 process ID that is assigned by the OS and distinguishes the process
1682 from all the other processes running on the same machine at the same
1686 @defun process-attributes pid
1687 This function returns an alist of attributes for the process specified
1688 by its process ID @var{pid}. Each association in the alist is of the
1689 form @code{(@var{key} . @var{value})}, where @var{key} designates the
1690 attribute and @var{value} is the value of that attribute. The various
1691 attribute @var{key}'s that this function can return are listed below.
1692 Not all platforms support all of these attributes; if an attribute is
1693 not supported, its association will not appear in the returned alist.
1694 Values that are numbers can be either integer or floating-point,
1695 depending on the magnitude of the value.
1699 The effective user ID of the user who invoked the process. The
1700 corresponding @var{value} is a number. If the process was invoked by
1701 the same user who runs the current Emacs session, the value is
1702 identical to what @code{user-uid} returns (@pxref{User
1706 User name corresponding to the process's effective user ID, a string.
1709 The group ID of the effective user ID, a number.
1712 Group name corresponding to the effective user's group ID, a string.
1715 The name of the command that runs in the process. This is a string
1716 that usually specifies the name of the executable file of the process,
1717 without the leading directories. However, some special system
1718 processes can report strings that do not correspond to an executable
1722 The state code of the process. This is a short string that encodes
1723 the scheduling state of the process. Here's a list of the most
1724 frequently seen codes:
1728 uninterruptible sleep (usually I/O)
1732 interruptible sleep (waiting for some event)
1734 stopped, e.g., by a job control signal
1736 ``zombie'': a process that terminated, but was not reaped by its parent
1740 For the full list of the possible states, see the manual page of the
1741 @command{ps} command.
1744 The process ID of the parent process, a number.
1747 The process group ID of the process, a number.
1750 The session ID of the process. This is a number that is the process
1751 ID of the process's @dfn{session leader}.
1754 A string that is the name of the process's controlling terminal. On
1755 Unix and GNU systems, this is normally the file name of the
1756 corresponding terminal device, such as @file{/dev/pts65}.
1759 The numerical process group ID of the foreground process group that
1760 uses the process's terminal.
1763 The number of minor page faults caused by the process since its
1764 beginning. (Minor page faults are those that don't involve reading
1768 The number of major page faults caused by the process since its
1769 beginning. (Major page faults require a disk to be read, and are thus
1770 more expensive than minor page faults.)
1774 Like @code{minflt} and @code{majflt}, but include the number of page
1775 faults for all the child processes of the given process.
1778 Time spent by the process in the user context, for running the
1779 application's code. The corresponding @var{value} is in the
1780 @w{@code{(@var{high} @var{low} @var{microsec})}} format, the same
1781 format used by functions @code{current-time} (@pxref{Time of Day,
1782 current-time}) and @code{file-attributes} (@pxref{File Attributes}).
1785 Time spent by the process in the system (kernel) context, for
1786 processing system calls. The corresponding @var{value} is in the same
1787 format as for @code{utime}.
1790 The sum of @code{utime} and @code{stime}. The corresponding
1791 @var{value} is in the same format as for @code{utime}.
1796 Like @code{utime}, @code{stime}, and @code{time}, but include the
1797 times of all the child processes of the given process.
1800 The numerical priority of the process.
1803 The @dfn{nice value} of the process, a number. (Processes with smaller
1804 nice values get scheduled more favorably.)
1807 The number of threads in the process.
1810 The time when the process was started, in the same
1811 @w{@code{(@var{high} @var{low} @var{microsec})}} format used by
1812 @code{current-time} and @code{file-attributes}.
1815 The time elapsed since the process started, in the @w{@code{(@var{high}
1816 @var{low} @var{microsec})}} format.
1819 The virtual memory size of the process, measured in kilobytes.
1822 The size of the process's @dfn{resident set}, the number of kilobytes
1823 occupied by the process in the machine's physical memory.
1826 The percentage of the CPU time used by the process since it started.
1827 The corresponding @var{value} is a floating-point number between 0 and
1831 The percentage of the total physical memory installed on the machine
1832 used by the process's resident set. The value is a floating-point
1833 number between 0 and 100.
1836 The command-line with which the process was invoked. This is a string
1837 in which individual command-line arguments are separated by blanks;
1838 whitespace characters that are embedded in the arguments are quoted as
1839 appropriate for the system's shell: escaped by backslash characters on
1840 GNU and Unix, and enclosed in double quote characters on Windows.
1841 Thus, this command-line string can be directly used in primitives such
1842 as @code{shell-command}.
1848 @node Transaction Queues
1849 @section Transaction Queues
1850 @cindex transaction queue
1852 You can use a @dfn{transaction queue} to communicate with a subprocess
1853 using transactions. First use @code{tq-create} to create a transaction
1854 queue communicating with a specified process. Then you can call
1855 @code{tq-enqueue} to send a transaction.
1857 @defun tq-create process
1858 This function creates and returns a transaction queue communicating with
1859 @var{process}. The argument @var{process} should be a subprocess
1860 capable of sending and receiving streams of bytes. It may be a child
1861 process, or it may be a TCP connection to a server, possibly on another
1865 @defun tq-enqueue queue question regexp closure fn &optional delay-question
1866 This function sends a transaction to queue @var{queue}. Specifying the
1867 queue has the effect of specifying the subprocess to talk to.
1869 The argument @var{question} is the outgoing message that starts the
1870 transaction. The argument @var{fn} is the function to call when the
1871 corresponding answer comes back; it is called with two arguments:
1872 @var{closure}, and the answer received.
1874 The argument @var{regexp} is a regular expression that should match
1875 text at the end of the entire answer, but nothing before; that's how
1876 @code{tq-enqueue} determines where the answer ends.
1878 If the argument @var{delay-question} is non-@code{nil}, delay sending
1879 this question until the process has finished replying to any previous
1880 questions. This produces more reliable results with some processes.
1882 The return value of @code{tq-enqueue} itself is not meaningful.
1885 @defun tq-close queue
1886 Shut down transaction queue @var{queue}, waiting for all pending transactions
1887 to complete, and then terminate the connection or child process.
1890 Transaction queues are implemented by means of a filter function.
1891 @xref{Filter Functions}.
1894 @section Network Connections
1895 @cindex network connection
1899 Emacs Lisp programs can open stream (TCP) and datagram (UDP) network
1900 connections to other processes on the same machine or other machines.
1901 A network connection is handled by Lisp much like a subprocess, and is
1902 represented by a process object. However, the process you are
1903 communicating with is not a child of the Emacs process, so it has no
1904 process @acronym{ID}, and you can't kill it or send it signals. All you
1905 can do is send and receive data. @code{delete-process} closes the
1906 connection, but does not kill the program at the other end; that
1907 program must decide what to do about closure of the connection.
1909 Lisp programs can listen for connections by creating network
1910 servers. A network server is also represented by a kind of process
1911 object, but unlike a network connection, the network server never
1912 transfers data itself. When it receives a connection request, it
1913 creates a new network connection to represent the connection just
1914 made. (The network connection inherits certain information, including
1915 the process plist, from the server.) The network server then goes
1916 back to listening for more connection requests.
1918 Network connections and servers are created by calling
1919 @code{make-network-process} with an argument list consisting of
1920 keyword/argument pairs, for example @code{:server t} to create a
1921 server process, or @code{:type 'datagram} to create a datagram
1922 connection. @xref{Low-Level Network}, for details. You can also use
1923 the @code{open-network-stream} function described below.
1925 To distinguish the different types of processes, the
1926 @code{process-type} function returns the symbol @code{network} for a
1927 network connection or server, @code{serial} for a serial port
1928 connection, or @code{real} for a real subprocess.
1930 The @code{process-status} function returns @code{open},
1931 @code{closed}, @code{connect}, and @code{failed} for network
1932 connections. For a network server, the status is always
1933 @code{listen}. None of those values is possible for a real
1934 subprocess. @xref{Process Information}.
1936 You can stop and resume operation of a network process by calling
1937 @code{stop-process} and @code{continue-process}. For a server
1938 process, being stopped means not accepting new connections. (Up to 5
1939 connection requests will be queued for when you resume the server; you
1940 can increase this limit, unless it is imposed by the operating
1941 system.) For a network stream connection, being stopped means not
1942 processing input (any arriving input waits until you resume the
1943 connection). For a datagram connection, some number of packets may be
1944 queued but input may be lost. You can use the function
1945 @code{process-command} to determine whether a network connection or
1946 server is stopped; a non-@code{nil} value means yes.
1948 @cindex network connection, encrypted
1949 @cindex encrypted network connections
1950 @cindex TLS network connections
1951 @cindex STARTTLS network connections
1952 @defun open-network-stream name buffer-or-name host service &rest parameters
1953 This function opens a TCP connection, with optional encryption, and
1954 returns a process object that represents the connection.
1956 The @var{name} argument specifies the name for the process object. It
1957 is modified as necessary to make it unique.
1959 The @var{buffer-or-name} argument is the buffer to associate with the
1960 connection. Output from the connection is inserted in the buffer,
1961 unless you specify a filter function to handle the output. If
1962 @var{buffer-or-name} is @code{nil}, it means that the connection is not
1963 associated with any buffer.
1965 The arguments @var{host} and @var{service} specify where to connect to;
1966 @var{host} is the host name (a string), and @var{service} is the name of
1967 a defined network service (a string) or a port number (an integer).
1969 @c FIXME? Is this too lengthy for the printed manual?
1970 The remaining arguments @var{parameters} are keyword/argument pairs
1971 that are mainly relevant to encrypted connections:
1975 @item :nowait @var{boolean}
1976 If non-@code{nil}, try to make an asynchronous connection.
1978 @item :type @var{type}
1979 The type of connection. Options are:
1983 An ordinary, unencrypted connection.
1986 A TLS (``Transport Layer Security'') connection.
1989 Start with a plain connection, and if parameters @samp{:success}
1990 and @samp{:capability-command} are supplied, try to upgrade to an encrypted
1991 connection via STARTTLS. If that fails, retain the unencrypted connection.
1993 As for @code{nil}, but if STARTTLS fails drop the connection.
1998 @item :always-query-capabilities @var{boolean}
1999 If non-@code{nil}, always ask for the server's capabilities, even when
2000 doing a @samp{plain} connection.
2002 @item :capability-command @var{capability-command}
2003 Command string to query the host capabilities.
2005 @item :end-of-command @var{regexp}
2006 @itemx :end-of-capability @var{regexp}
2007 Regular expression matching the end of a command, or the end of the
2008 command @var{capability-command}. The latter defaults to the former.
2010 @item :starttls-function @var{function}
2011 Function of one argument (the response to @var{capability-command}),
2012 which returns either @code{nil}, or the command to activate STARTTLS
2015 @item :success @var{regexp}
2016 Regular expression matching a successful STARTTLS negotiation.
2018 @item :use-starttls-if-possible @var{boolean}
2019 If non-@code{nil}, do opportunistic STARTTLS upgrades even if Emacs
2020 doesn't have built-in TLS support.
2022 @item :client-certificate @var{list-or-t}
2023 Either a list of the form @code{(@var{key-file} @var{cert-file})},
2024 naming the certificate key file and certificate file itself, or
2025 @code{t}, meaning to query @code{auth-source} for this information
2026 (@pxref{Top,,auth-source, auth, Emacs auth-source Library}).
2027 Only used for TLS or STARTTLS.
2029 @item :return-list @var{cons-or-nil}
2030 The return value of this function. If omitted or @code{nil}, return a
2031 process object. Otherwise, a cons of the form @code{(@var{process-object}
2032 . @var{plist})}, where @var{plist} has keywords:
2035 @item :greeting @var{string-or-nil}
2036 If non-@code{nil}, the greeting string returned by the host.
2037 @item :capabilities @var{string-or-nil}
2038 If non-@code{nil}, the host's capability string.
2039 @item :type @var{symbol}
2040 The connection type: @samp{plain} or @samp{tls}.
2047 @node Network Servers
2048 @section Network Servers
2049 @cindex network servers
2051 You create a server by calling @code{make-network-process} with
2052 @code{:server t}. The server will listen for connection requests from
2053 clients. When it accepts a client connection request, that creates a
2054 new network connection, itself a process object, with the following
2059 The connection's process name is constructed by concatenating the
2060 server process's @var{name} with a client identification string. The
2061 client identification string for an IPv4 connection looks like
2062 @samp{<@var{a}.@var{b}.@var{c}.@var{d}:@var{p}>}. Otherwise, it is a
2063 unique number in brackets, as in @samp{<@var{nnn}>}. The number
2064 is unique for each connection in the Emacs session.
2067 If the server's filter is non-@code{nil}, the connection process does
2068 not get a separate process buffer; otherwise, Emacs creates a new
2069 buffer for the purpose. The buffer name is the server's buffer name
2070 or process name, concatenated with the client identification string.
2072 The server's process buffer value is never used directly, but the log
2073 function can retrieve it and use it to log connections by inserting
2077 The communication type and the process filter and sentinel are
2078 inherited from those of the server. The server never directly
2079 uses its filter and sentinel; their sole purpose is to initialize
2080 connections made to the server.
2083 The connection's process contact info is set according to the client's
2084 addressing information (typically an IP address and a port number).
2085 This information is associated with the @code{process-contact}
2086 keywords @code{:host}, @code{:service}, @code{:remote}.
2089 The connection's local address is set up according to the port
2090 number used for the connection.
2093 The client process's plist is initialized from the server's plist.
2100 A datagram connection communicates with individual packets rather
2101 than streams of data. Each call to @code{process-send} sends one
2102 datagram packet (@pxref{Input to Processes}), and each datagram
2103 received results in one call to the filter function.
2105 The datagram connection doesn't have to talk with the same remote
2106 peer all the time. It has a @dfn{remote peer address} which specifies
2107 where to send datagrams to. Each time an incoming datagram is passed
2108 to the filter function, the peer address is set to the address that
2109 datagram came from; that way, if the filter function sends a datagram,
2110 it will go back to that place. You can specify the remote peer
2111 address when you create the datagram connection using the
2112 @code{:remote} keyword. You can change it later on by calling
2113 @code{set-process-datagram-address}.
2115 @defun process-datagram-address process
2116 If @var{process} is a datagram connection or server, this function
2117 returns its remote peer address.
2120 @defun set-process-datagram-address process address
2121 If @var{process} is a datagram connection or server, this function
2122 sets its remote peer address to @var{address}.
2125 @node Low-Level Network
2126 @section Low-Level Network Access
2128 You can also create network connections by operating at a lower
2129 level than that of @code{open-network-stream}, using
2130 @code{make-network-process}.
2133 * Proc: Network Processes. Using @code{make-network-process}.
2134 * Options: Network Options. Further control over network connections.
2135 * Features: Network Feature Testing.
2136 Determining which network features work on
2137 the machine you are using.
2140 @node Network Processes
2141 @subsection @code{make-network-process}
2143 The basic function for creating network connections and network
2144 servers is @code{make-network-process}. It can do either of those
2145 jobs, depending on the arguments you give it.
2147 @defun make-network-process &rest args
2148 This function creates a network connection or server and returns the
2149 process object that represents it. The arguments @var{args} are a
2150 list of keyword/argument pairs. Omitting a keyword is always
2151 equivalent to specifying it with value @code{nil}, except for
2152 @code{:coding}, @code{:filter-multibyte}, and @code{:reuseaddr}. Here
2153 are the meaningful keywords:
2156 @item :name @var{name}
2157 Use the string @var{name} as the process name. It is modified if
2158 necessary to make it unique.
2160 @item :type @var{type}
2161 Specify the communication type. A value of @code{nil} specifies a
2162 stream connection (the default); @code{datagram} specifies a datagram
2163 connection; @code{seqpacket} specifies a ``sequenced packet stream''
2164 connection. Both connections and servers can be of these types.
2166 @item :server @var{server-flag}
2167 If @var{server-flag} is non-@code{nil}, create a server. Otherwise,
2168 create a connection. For a stream type server, @var{server-flag} may
2169 be an integer which then specifies the length of the queue of pending
2170 connections to the server. The default queue length is 5.
2172 @item :host @var{host}
2173 Specify the host to connect to. @var{host} should be a host name or
2174 Internet address, as a string, or the symbol @code{local} to specify
2175 the local host. If you specify @var{host} for a server, it must
2176 specify a valid address for the local host, and only clients
2177 connecting to that address will be accepted.
2179 @item :service @var{service}
2180 @var{service} specifies a port number to connect to, or, for a server,
2181 the port number to listen on. It should be a service name that
2182 translates to a port number, or an integer specifying the port number
2183 directly. For a server, it can also be @code{t}, which means to let
2184 the system select an unused port number.
2186 @item :family @var{family}
2187 @var{family} specifies the address (and protocol) family for
2188 communication. @code{nil} means determine the proper address family
2189 automatically for the given @var{host} and @var{service}.
2190 @code{local} specifies a Unix socket, in which case @var{host} is
2191 ignored. @code{ipv4} and @code{ipv6} specify to use IPv4 and IPv6
2194 @item :local @var{local-address}
2195 For a server process, @var{local-address} is the address to listen on.
2196 It overrides @var{family}, @var{host} and @var{service}, and you
2197 may as well not specify them.
2199 @item :remote @var{remote-address}
2200 For a connection, @var{remote-address} is the address to connect to.
2201 It overrides @var{family}, @var{host} and @var{service}, and you
2202 may as well not specify them.
2204 For a datagram server, @var{remote-address} specifies the initial
2205 setting of the remote datagram address.
2207 The format of @var{local-address} or @var{remote-address} depends on
2212 An IPv4 address is represented as a five-element vector of four 8-bit
2213 integers and one 16-bit integer
2214 @code{[@var{a} @var{b} @var{c} @var{d} @var{p}]} corresponding to
2215 numeric IPv4 address @var{a}.@var{b}.@var{c}.@var{d} and port number
2219 An IPv6 address is represented as a nine-element vector of 16-bit
2220 integers @code{[@var{a} @var{b} @var{c} @var{d} @var{e} @var{f}
2221 @var{g} @var{h} @var{p}]} corresponding to numeric IPv6 address
2222 @var{a}:@var{b}:@var{c}:@var{d}:@var{e}:@var{f}:@var{g}:@var{h} and
2223 port number @var{p}.
2226 A local address is represented as a string which specifies the address
2227 in the local address space.
2230 An ``unsupported family'' address is represented by a cons
2231 @code{(@var{f} . @var{av})}, where @var{f} is the family number and
2232 @var{av} is a vector specifying the socket address using one element
2233 per address data byte. Do not rely on this format in portable code,
2234 as it may depend on implementation defined constants, data sizes, and
2235 data structure alignment.
2238 @item :nowait @var{bool}
2239 If @var{bool} is non-@code{nil} for a stream connection, return
2240 without waiting for the connection to complete. When the connection
2241 succeeds or fails, Emacs will call the sentinel function, with a
2242 second argument matching @code{"open"} (if successful) or
2243 @code{"failed"}. The default is to block, so that
2244 @code{make-network-process} does not return until the connection
2245 has succeeded or failed.
2247 @item :stop @var{stopped}
2248 Start the network connection or server in the `stopped' state if
2249 @var{stopped} is non-@code{nil}.
2251 @item :buffer @var{buffer}
2252 Use @var{buffer} as the process buffer.
2254 @item :coding @var{coding}
2255 Use @var{coding} as the coding system for this process. To specify
2256 different coding systems for decoding data from the connection and for
2257 encoding data sent to it, specify @code{(@var{decoding} .
2258 @var{encoding})} for @var{coding}.
2260 If you don't specify this keyword at all, the default
2261 is to determine the coding systems from the data.
2263 @item :noquery @var{query-flag}
2264 Initialize the process query flag to @var{query-flag}.
2265 @xref{Query Before Exit}.
2267 @item :filter @var{filter}
2268 Initialize the process filter to @var{filter}.
2270 @item :sentinel @var{sentinel}
2271 Initialize the process sentinel to @var{sentinel}.
2273 @item :log @var{log}
2274 Initialize the log function of a server process to @var{log}. The log
2275 function is called each time the server accepts a network connection
2276 from a client. The arguments passed to the log function are
2277 @var{server}, @var{connection}, and @var{message}, where @var{server}
2278 is the server process, @var{connection} is the new process for the
2279 connection, and @var{message} is a string describing what has
2282 @item :plist @var{plist}
2283 Initialize the process plist to @var{plist}.
2286 The original argument list, modified with the actual connection
2287 information, is available via the @code{process-contact} function.
2290 @node Network Options
2291 @subsection Network Options
2293 The following network options can be specified when you create a
2294 network process. Except for @code{:reuseaddr}, you can also set or
2295 modify these options later, using @code{set-network-process-option}.
2297 For a server process, the options specified with
2298 @code{make-network-process} are not inherited by the client
2299 connections, so you will need to set the necessary options for each
2300 child connection as it is created.
2303 @item :bindtodevice @var{device-name}
2304 If @var{device-name} is a non-empty string identifying a network
2305 interface name (see @code{network-interface-list}), only handle
2306 packets received on that interface. If @var{device-name} is @code{nil}
2307 (the default), handle packets received on any interface.
2309 Using this option may require special privileges on some systems.
2311 @item :broadcast @var{broadcast-flag}
2312 If @var{broadcast-flag} is non-@code{nil} for a datagram process, the
2313 process will receive datagram packet sent to a broadcast address, and
2314 be able to send packets to a broadcast address. Ignored for a stream
2317 @item :dontroute @var{dontroute-flag}
2318 If @var{dontroute-flag} is non-@code{nil}, the process can only send
2319 to hosts on the same network as the local host.
2321 @item :keepalive @var{keepalive-flag}
2322 If @var{keepalive-flag} is non-@code{nil} for a stream connection,
2323 enable exchange of low-level keep-alive messages.
2325 @item :linger @var{linger-arg}
2326 If @var{linger-arg} is non-@code{nil}, wait for successful
2327 transmission of all queued packets on the connection before it is
2328 deleted (see @code{delete-process}). If @var{linger-arg} is an
2329 integer, it specifies the maximum time in seconds to wait for queued
2330 packets to be sent before closing the connection. Default is
2331 @code{nil} which means to discard unsent queued packets when the
2334 @item :oobinline @var{oobinline-flag}
2335 If @var{oobinline-flag} is non-@code{nil} for a stream connection,
2336 receive out-of-band data in the normal data stream. Otherwise, ignore
2339 @item :priority @var{priority}
2340 Set the priority for packets sent on this connection to the integer
2341 @var{priority}. The interpretation of this number is protocol
2342 specific, such as setting the TOS (type of service) field on IP
2343 packets sent on this connection. It may also have system dependent
2344 effects, such as selecting a specific output queue on the network
2347 @item :reuseaddr @var{reuseaddr-flag}
2348 If @var{reuseaddr-flag} is non-@code{nil} (the default) for a stream
2349 server process, allow this server to reuse a specific port number (see
2350 @code{:service}) unless another process on this host is already
2351 listening on that port. If @var{reuseaddr-flag} is @code{nil}, there
2352 may be a period of time after the last use of that port (by any
2353 process on the host), where it is not possible to make a new server on
2357 @defun set-network-process-option process option value &optional no-error
2358 This function sets or modifies a network option for network process
2359 @var{process}. See @code{make-network-process} for details of options
2360 @var{option} and their corresponding values @var{value}. If
2361 @var{no-error} is non-@code{nil}, this function returns @code{nil}
2362 instead of signaling an error if @var{option} is not a supported
2363 option. If the function successfully completes, it returns @code{t}.
2365 The current setting of an option is available via the
2366 @code{process-contact} function.
2369 @node Network Feature Testing
2370 @subsection Testing Availability of Network Features
2372 To test for the availability of a given network feature, use
2373 @code{featurep} like this:
2376 (featurep 'make-network-process '(@var{keyword} @var{value}))
2380 The result of the first form is @code{t} if it works to specify
2381 @var{keyword} with value @var{value} in @code{make-network-process}.
2382 The result of the second form is @code{t} if @var{keyword} is
2383 supported by @code{make-network-process}. Here are some of the
2384 @var{keyword}---@var{value} pairs you can test in
2389 Non-@code{nil} if non-blocking connect is supported.
2390 @item (:type datagram)
2391 Non-@code{nil} if datagrams are supported.
2392 @item (:family local)
2393 Non-@code{nil} if local (a.k.a.@: ``UNIX domain'') sockets are supported.
2394 @item (:family ipv6)
2395 Non-@code{nil} if IPv6 is supported.
2397 Non-@code{nil} if the system can select the port for a server.
2400 To test for the availability of a given network option, use
2401 @code{featurep} like this:
2404 (featurep 'make-network-process '@var{keyword})
2408 Here are some of the options you can test in this way.
2419 That particular network option is supported by
2420 @code{make-network-process} and @code{set-network-process-option}.
2424 @section Misc Network Facilities
2426 These additional functions are useful for creating and operating
2427 on network connections. Note that they are supported only on some
2430 @defun network-interface-list
2431 This function returns a list describing the network interfaces
2432 of the machine you are using. The value is an alist whose
2433 elements have the form @code{(@var{name} . @var{address})}.
2434 @var{address} has the same form as the @var{local-address}
2435 and @var{remote-address} arguments to @code{make-network-process}.
2438 @defun network-interface-info ifname
2439 This function returns information about the network interface named
2440 @var{ifname}. The value is a list of the form
2441 @code{(@var{addr} @var{bcast} @var{netmask} @var{hwaddr} @var{flags})}.
2445 The Internet protocol address.
2447 The broadcast address.
2451 The layer 2 address (Ethernet MAC address, for instance).
2453 The current flags of the interface.
2457 @defun format-network-address address &optional omit-port
2458 This function converts the Lisp representation of a network address to
2461 A five-element vector @code{[@var{a} @var{b} @var{c} @var{d} @var{p}]}
2462 represents an IPv4 address @var{a}.@var{b}.@var{c}.@var{d} and port
2463 number @var{p}. @code{format-network-address} converts that to the
2464 string @code{"@var{a}.@var{b}.@var{c}.@var{d}:@var{p}"}.
2466 A nine-element vector @code{[@var{a} @var{b} @var{c} @var{d} @var{e}
2467 @var{f} @var{g} @var{h} @var{p}]} represents an IPv6 address along
2468 with a port number. @code{format-network-address} converts that to
2470 @code{"[@var{a}:@var{b}:@var{c}:@var{d}:@var{e}:@var{f}:@var{g}:@var{h}]:@var{p}"}.
2472 If the vector does not include the port number, @var{p}, or if
2473 @var{omit-port} is non-@code{nil}, the result does not include the
2474 @code{:@var{p}} suffix.
2478 @section Communicating with Serial Ports
2479 @cindex @file{/dev/tty}
2481 @cindex serial connections
2483 Emacs can communicate with serial ports. For interactive use,
2484 @kbd{M-x serial-term} opens a terminal window. In a Lisp program,
2485 @code{make-serial-process} creates a process object.
2487 The serial port can be configured at run-time, without having to
2488 close and re-open it. The function @code{serial-process-configure}
2489 lets you change the speed, bytesize, and other parameters. In a
2490 terminal window created by @code{serial-term}, you can click on the
2491 mode line for configuration.
2493 A serial connection is represented by a process object which can be
2494 used similar to a subprocess or network process. You can send and
2495 receive data and configure the serial port. A serial process object
2496 has no process ID, you can't send signals to it, and the status codes
2497 are different from other types of processes.
2498 @code{delete-process} on the process object or @code{kill-buffer} on
2499 the process buffer close the connection, but this does not affect the
2500 device connected to the serial port.
2502 The function @code{process-type} returns the symbol @code{serial}
2503 for a process object representing a serial port connection.
2505 Serial ports are available on GNU/Linux, Unix, and Windows systems.
2507 @deffn Command serial-term port speed
2508 Start a terminal-emulator for a serial port in a new buffer.
2509 @var{port} is the name of the serial port to which to connect. For
2510 example, this could be @file{/dev/ttyS0} on Unix. On Windows, this
2511 could be @file{COM1}, or @file{\\.\COM10} (double the backslashes in
2514 @var{speed} is the speed of the serial port in bits per second. 9600
2515 is a common value. The buffer is in Term mode; see @ref{Term Mode,,,
2516 emacs, The GNU Emacs Manual}, for the commands to use in that buffer.
2517 You can change the speed and the configuration in the mode line menu.
2520 @defun make-serial-process &rest args
2521 This function creates a process and a buffer. Arguments are specified
2522 as keyword/argument pairs. Here's the list of the meaningful keywords:
2525 @item :port @var{port}@r{ (mandatory)}
2526 This is the name of the serial port. On Unix and GNU systems, this is
2527 a file name such as @file{/dev/ttyS0}. On Windows, this could be
2528 @file{COM1}, or @file{\\.\COM10} for ports higher than @file{COM9}
2529 (double the backslashes in Lisp strings).
2531 @item :speed @var{speed}@r{ (mandatory)}
2532 The speed of the serial port in bits per second. This function calls
2533 @code{serial-process-configure} to handle the speed.
2535 @item :name @var{name}
2536 The name of the process. If @var{name} is not given, @var{port} will
2537 serve as the process name as well.
2539 @item :buffer @var{buffer}
2540 The buffer to associate with the process. The value could be either a
2541 buffer or a string that names a buffer. Process output goes at the
2542 end of that buffer, unless you specify an output stream or filter
2543 function to handle the output. If @var{buffer} is not given, the
2544 process buffer's name is taken from the value of the @code{:name}
2547 @item :coding @var{coding}
2548 If @var{coding} is a symbol, it specifies the coding system used for
2549 both reading and writing for this process. If @var{coding} is a cons
2550 @code{(decoding . encoding)}, @var{decoding} is used for reading, and
2551 @var{encoding} is used for writing. If not specified, the default is
2552 to determine the coding systems from data itself.
2554 @item :noquery @var{query-flag}
2555 Initialize the process query flag to @var{query-flag}. @xref{Query
2556 Before Exit}. The flags defaults to @code{nil} if unspecified.
2558 @item :stop @var{bool}
2559 Start process in the @code{stopped} state if @var{bool} is
2560 non-@code{nil}. In the stopped state, a serial process does not
2561 accept incoming data, but you can send outgoing data. The stopped
2562 state is cleared by @code{continue-process} and set by
2563 @code{stop-process}.
2565 @item :filter @var{filter}
2566 Install @var{filter} as the process filter.
2568 @item :sentinel @var{sentinel}
2569 Install @var{sentinel} as the process sentinel.
2571 @item :plist @var{plist}
2572 Install @var{plist} as the initial plist of the process.
2579 These are handled by @code{serial-process-configure}, which is called
2580 by @code{make-serial-process}.
2583 The original argument list, possibly modified by later configuration,
2584 is available via the function @code{process-contact}.
2589 (make-serial-process :port "/dev/ttyS0" :speed 9600)
2593 @defun serial-process-configure &rest args
2594 @cindex baud, in serial connections
2595 @cindex bytesize, in serial connections
2596 @cindex parity, in serial connections
2597 @cindex stopbits, in serial connections
2598 @cindex flowcontrol, in serial connections
2600 This functions configures a serial port connection. Arguments are
2601 specified as keyword/argument pairs. Attributes that are not given
2602 are re-initialized from the process's current configuration (available
2603 via the function @code{process-contact}) or set to reasonable default
2604 values. The following arguments are defined:
2607 @item :process @var{process}
2608 @itemx :name @var{name}
2609 @itemx :buffer @var{buffer}
2610 @itemx :port @var{port}
2611 Any of these arguments can be given to identify the process that is to
2612 be configured. If none of these arguments is given, the current
2613 buffer's process is used.
2615 @item :speed @var{speed}
2616 The speed of the serial port in bits per second, a.k.a.@: @dfn{baud
2617 rate}. The value can be any number, but most serial ports work only
2618 at a few defined values between 1200 and 115200, with 9600 being the
2619 most common value. If @var{speed} is @code{nil}, the function ignores
2620 all other arguments and does not configure the port. This may be
2621 useful for special serial ports such as Bluetooth-to-serial converters
2622 which can only be configured through AT commands sent through the
2623 connection. The value of @code{nil} for @var{speed} is valid only for
2624 connections that were already opened by a previous call to
2625 @code{make-serial-process} or @code{serial-term}.
2627 @item :bytesize @var{bytesize}
2628 The number of bits per byte, which can be 7 or 8. If @var{bytesize}
2629 is not given or @code{nil}, it defaults to 8.
2631 @item :parity @var{parity}
2632 The value can be @code{nil} (don't use parity), the symbol
2633 @code{odd} (use odd parity), or the symbol @code{even} (use even
2634 parity). If @var{parity} is not given, it defaults to no parity.
2636 @item :stopbits @var{stopbits}
2637 The number of stopbits used to terminate a transmission
2638 of each byte. @var{stopbits} can be 1 or 2. If @var{stopbits} is not
2639 given or @code{nil}, it defaults to 1.
2641 @item :flowcontrol @var{flowcontrol}
2642 The type of flow control to use for this connection, which is either
2643 @code{nil} (don't use flow control), the symbol @code{hw} (use RTS/CTS
2644 hardware flow control), or the symbol @code{sw} (use XON/XOFF software
2645 flow control). If @var{flowcontrol} is not given, it defaults to no
2649 @code{serial-process-configure} is called by
2650 @code{make-serial-process} for the initial configuration of the serial
2655 @section Packing and Unpacking Byte Arrays
2656 @cindex byte packing and unpacking
2658 This section describes how to pack and unpack arrays of bytes,
2659 usually for binary network protocols. These functions convert byte arrays
2660 to alists, and vice versa. The byte array can be represented as a
2661 unibyte string or as a vector of integers, while the alist associates
2662 symbols either with fixed-size objects or with recursive sub-alists.
2665 @cindex deserializing
2668 Conversion from byte arrays to nested alists is also known as
2669 @dfn{deserializing} or @dfn{unpacking}, while going in the opposite
2670 direction is also known as @dfn{serializing} or @dfn{packing}.
2673 * Bindat Spec:: Describing data layout.
2674 * Bindat Functions:: Doing the unpacking and packing.
2675 * Bindat Examples:: Samples of what bindat.el can do for you!
2679 @subsection Describing Data Layout
2681 To control unpacking and packing, you write a @dfn{data layout
2682 specification}, a special nested list describing named and typed
2683 @dfn{fields}. This specification controls length of each field to be
2684 processed, and how to pack or unpack it. We normally keep bindat specs
2685 in variables whose names end in @samp{-bindat-spec}; that kind of name
2686 is automatically recognized as ``risky''.
2690 @cindex little endian
2691 @cindex network byte ordering
2692 A field's @dfn{type} describes the size (in bytes) of the object
2693 that the field represents and, in the case of multibyte fields, how
2694 the bytes are ordered within the field. The two possible orderings
2695 are ``big endian'' (also known as ``network byte ordering'') and
2696 ``little endian''. For instance, the number @code{#x23cd} (decimal
2697 9165) in big endian would be the two bytes @code{#x23} @code{#xcd};
2698 and in little endian, @code{#xcd} @code{#x23}. Here are the possible
2704 Unsigned byte, with length 1.
2709 Unsigned integer in network byte order, with length 2.
2712 Unsigned integer in network byte order, with length 3.
2717 Unsigned integer in network byte order, with length 4.
2718 Note: These values may be limited by Emacs's integer implementation limits.
2723 Unsigned integer in little endian order, with length 2, 3 and 4, respectively.
2726 String of length @var{len}.
2728 @item strz @var{len}
2729 Zero-terminated string, in a fixed-size field with length @var{len}.
2731 @item vec @var{len} [@var{type}]
2732 Vector of @var{len} elements of type @var{type}, or bytes if not
2733 @var{type} is specified.
2734 The @var{type} is any of the simple types above, or another vector
2735 specified as a list @code{(vec @var{len} [@var{type}])}.
2738 Four-byte vector representing an Internet address. For example:
2739 @code{[127 0 0 1]} for localhost.
2741 @item bits @var{len}
2742 List of set bits in @var{len} bytes. The bytes are taken in big
2743 endian order and the bits are numbered starting with @code{8 *
2744 @var{len} @minus{} 1} and ending with zero. For example: @code{bits
2745 2} unpacks @code{#x28} @code{#x1c} to @code{(2 3 4 11 13)} and
2746 @code{#x1c} @code{#x28} to @code{(3 5 10 11 12)}.
2748 @item (eval @var{form})
2749 @var{form} is a Lisp expression evaluated at the moment the field is
2750 unpacked or packed. The result of the evaluation should be one of the
2751 above-listed type specifications.
2754 For a fixed-size field, the length @var{len} is given as an integer
2755 specifying the number of bytes in the field.
2757 When the length of a field is not fixed, it typically depends on the
2758 value of a preceding field. In this case, the length @var{len} can be
2759 given either as a list @code{(@var{name} ...)} identifying a
2760 @dfn{field name} in the format specified for @code{bindat-get-field}
2761 below, or by an expression @code{(eval @var{form})} where @var{form}
2762 should evaluate to an integer, specifying the field length.
2764 A field specification generally has the form @code{([@var{name}]
2765 @var{handler})}. The square braces indicate that @var{name} is
2766 optional. (Don't use names that are symbols meaningful as type
2767 specifications (above) or handler specifications (below), since that
2768 would be ambiguous.) @var{name} can be a symbol or the expression
2769 @code{(eval @var{form})}, in which case @var{form} should evaluate to
2772 @var{handler} describes how to unpack or pack the field and can be one
2777 Unpack/pack this field according to the type specification @var{type}.
2779 @item eval @var{form}
2780 Evaluate @var{form}, a Lisp expression, for side-effect only. If the
2781 field name is specified, the value is bound to that field name.
2783 @item fill @var{len}
2784 Skip @var{len} bytes. In packing, this leaves them unchanged,
2785 which normally means they remain zero. In unpacking, this means
2788 @item align @var{len}
2789 Skip to the next multiple of @var{len} bytes.
2791 @item struct @var{spec-name}
2792 Process @var{spec-name} as a sub-specification. This describes a
2793 structure nested within another structure.
2795 @item union @var{form} (@var{tag} @var{spec})@dots{}
2796 @c ??? I don't see how one would actually use this.
2797 @c ??? what kind of expression would be useful for @var{form}?
2798 Evaluate @var{form}, a Lisp expression, find the first @var{tag}
2799 that matches it, and process its associated data layout specification
2800 @var{spec}. Matching can occur in one of three ways:
2804 If a @var{tag} has the form @code{(eval @var{expr})}, evaluate
2805 @var{expr} with the variable @code{tag} dynamically bound to the value
2806 of @var{form}. A non-@code{nil} result indicates a match.
2809 @var{tag} matches if it is @code{equal} to the value of @var{form}.
2812 @var{tag} matches unconditionally if it is @code{t}.
2815 @item repeat @var{count} @var{field-specs}@dots{}
2816 Process the @var{field-specs} recursively, in order, then repeat
2817 starting from the first one, processing all the specs @var{count}
2818 times overall. The @var{count} is given using the same formats as a
2819 field length---if an @code{eval} form is used, it is evaluated just once.
2820 For correct operation, each spec in @var{field-specs} must include a name.
2823 For the @code{(eval @var{form})} forms used in a bindat specification,
2824 the @var{form} can access and update these dynamically bound variables
2829 Value of the last field processed.
2832 The data as a byte array.
2835 Current index (within @code{bindat-raw}) for unpacking or packing.
2838 The alist containing the structured data that have been unpacked so
2839 far, or the entire structure being packed. You can use
2840 @code{bindat-get-field} to access specific fields of this structure.
2844 Inside a @code{repeat} block, these contain the maximum number of
2845 repetitions (as specified by the @var{count} parameter), and the
2846 current repetition number (counting from 0). Setting @code{count} to
2847 zero will terminate the inner-most repeat block after the current
2848 repetition has completed.
2851 @node Bindat Functions
2852 @subsection Functions to Unpack and Pack Bytes
2854 In the following documentation, @var{spec} refers to a data layout
2855 specification, @code{bindat-raw} to a byte array, and @var{struct} to an
2856 alist representing unpacked field data.
2858 @defun bindat-unpack spec bindat-raw &optional bindat-idx
2859 This function unpacks data from the unibyte string or byte
2860 array @code{bindat-raw}
2861 according to @var{spec}. Normally this starts unpacking at the
2862 beginning of the byte array, but if @var{bindat-idx} is non-@code{nil}, it
2863 specifies a zero-based starting position to use instead.
2865 The value is an alist or nested alist in which each element describes
2869 @defun bindat-get-field struct &rest name
2870 This function selects a field's data from the nested alist
2871 @var{struct}. Usually @var{struct} was returned by
2872 @code{bindat-unpack}. If @var{name} corresponds to just one argument,
2873 that means to extract a top-level field value. Multiple @var{name}
2874 arguments specify repeated lookup of sub-structures. An integer name
2875 acts as an array index.
2877 For example, if @var{name} is @code{(a b 2 c)}, that means to find
2878 field @code{c} in the third element of subfield @code{b} of field
2879 @code{a}. (This corresponds to @code{struct.a.b[2].c} in C.)
2882 Although packing and unpacking operations change the organization of
2883 data (in memory), they preserve the data's @dfn{total length}, which is
2884 the sum of all the fields' lengths, in bytes. This value is not
2885 generally inherent in either the specification or alist alone; instead,
2886 both pieces of information contribute to its calculation. Likewise, the
2887 length of a string or array being unpacked may be longer than the data's
2888 total length as described by the specification.
2890 @defun bindat-length spec struct
2891 This function returns the total length of the data in @var{struct},
2892 according to @var{spec}.
2895 @defun bindat-pack spec struct &optional bindat-raw bindat-idx
2896 This function returns a byte array packed according to @var{spec} from
2897 the data in the alist @var{struct}. Normally it creates and fills a
2898 new byte array starting at the beginning. However, if @var{bindat-raw}
2899 is non-@code{nil}, it specifies a pre-allocated unibyte string or vector to
2900 pack into. If @var{bindat-idx} is non-@code{nil}, it specifies the starting
2901 offset for packing into @code{bindat-raw}.
2903 When pre-allocating, you should make sure @code{(length @var{bindat-raw})}
2904 meets or exceeds the total length to avoid an out-of-range error.
2907 @defun bindat-ip-to-string ip
2908 Convert the Internet address vector @var{ip} to a string in the usual
2912 (bindat-ip-to-string [127 0 0 1])
2913 @result{} "127.0.0.1"
2917 @node Bindat Examples
2918 @subsection Examples of Byte Unpacking and Packing
2920 Here is a complete example of byte unpacking and packing:
2923 (defvar fcookie-index-spec
2931 (:offset repeat (:count)
2933 "Description of a fortune cookie index file's contents.")
2935 (defun fcookie (cookies &optional index)
2936 "Display a random fortune cookie from file COOKIES.
2937 Optional second arg INDEX specifies the associated index
2938 filename, which is by default constructed by appending
2939 \".dat\" to COOKIES. Display cookie text in possibly
2940 new buffer \"*Fortune Cookie: BASENAME*\" where BASENAME
2941 is COOKIES without the directory part."
2942 (interactive "fCookies file: ")
2943 (let* ((info (with-temp-buffer
2944 (insert-file-contents-literally
2945 (or index (concat cookies ".dat")))
2946 (bindat-unpack fcookie-index-spec
2948 (sel (random (bindat-get-field info :count)))
2949 (beg (cdar (bindat-get-field info :offset sel)))
2950 (end (or (cdar (bindat-get-field info
2952 (nth 7 (file-attributes cookies)))))
2955 (format "*Fortune Cookie: %s*"
2956 (file-name-nondirectory cookies))))
2958 (insert-file-contents-literally
2959 cookies nil beg (- end 3))))
2961 (defun fcookie-create-index (cookies &optional index delim)
2962 "Scan file COOKIES, and write out its index file.
2963 Optional second arg INDEX specifies the index filename,
2964 which is by default constructed by appending \".dat\" to
2965 COOKIES. Optional third arg DELIM specifies the unibyte
2966 character which, when found on a line of its own in
2967 COOKIES, indicates the border between entries."
2968 (interactive "fCookies file: ")
2969 (setq delim (or delim ?%))
2970 (let ((delim-line (format "\n%c\n" delim))
2973 min p q len offsets)
2974 (unless (= 3 (string-bytes delim-line))
2975 (error "Delimiter cannot be represented in one byte"))
2977 (insert-file-contents-literally cookies)
2978 (while (and (setq p (point))
2979 (search-forward delim-line (point-max) t)
2980 (setq len (- (point) 3 p)))
2981 (setq count (1+ count)
2983 min (min (or min max) len)
2984 offsets (cons (1- p) offsets))))
2986 (set-buffer-multibyte nil)
2996 (:offset . ,(mapcar (lambda (o)
2997 (list (cons :foo o)))
2998 (nreverse offsets))))))
2999 (let ((coding-system-for-write 'raw-text-unix))
3000 (write-file (or index (concat cookies ".dat")))))))
3003 Following is an example of defining and unpacking a complex structure.
3004 Consider the following C structures:
3008 unsigned long dest_ip;
3009 unsigned long src_ip;
3010 unsigned short dest_port;
3011 unsigned short src_port;
3016 unsigned char opcode;
3017 unsigned short length; /* In network byte order */
3018 unsigned char id[8]; /* null-terminated string */
3019 unsigned char data[/* (length + 3) & ~3 */];
3023 struct header header;
3024 unsigned long counters[2]; /* In little endian order */
3025 unsigned char items;
3026 unsigned char filler[3];
3027 struct data item[/* items */];
3032 The corresponding data layout specification:
3044 (length u16) ;; network byte order
3050 '((header struct header-spec)
3051 (counters vec 2 u32r) ;; little endian order
3054 (item repeat (items)
3055 (struct data-spec))))
3058 A binary data representation:
3062 [ 192 168 1 100 192 168 1 101 01 28 21 32
3063 160 134 1 0 5 1 0 0 2 0 0 0
3064 2 3 0 5 ?A ?B ?C ?D ?E ?F 0 0 1 2 3 4 5 0 0 0
3065 1 4 0 7 ?B ?C ?D ?E ?F ?G 0 0 6 7 8 9 10 11 12 0 ])
3068 The corresponding decoded structure:
3071 (setq decoded (bindat-unpack packet-spec binary-data))
3074 (dest-ip . [192 168 1 100])
3075 (src-ip . [192 168 1 101])
3078 (counters . [100000 261])
3080 (item ((data . [1 2 3 4 5])
3085 ((data . [6 7 8 9 10 11 12])
3092 Fetching data from this structure:
3095 (bindat-get-field decoded 'item 1 'id)