Next: Shell Arguments, Up: Processes   [Contents][Index]

41.1 Functions that Create Subprocesses ¶

There are three primitives that create a new subprocess in which to run a program. One of them, make-process, creates an asynchronous process and returns a process object (see Creating an Asynchronous Process). The other two, call-process and call-process-region, create a synchronous process and do not return a process object (see Creating a Synchronous Process). There are various higher-level functions that make use of these primitives to run particular types of process.

Synchronous and asynchronous processes are explained in the following sections. Since the three functions are all called in a similar fashion, their common arguments are described here.

In all cases, the functions specify the program to be run. An error is signaled if the file is not found or cannot be executed. If the file name is relative, the variable exec-path contains a list of directories to search. Emacs initializes exec-path when it starts up, based on the value of the environment variable PATH. The standard file name constructs, ‘~’, ‘.’, and ‘..’, are interpreted as usual in exec-path, but environment variable substitutions (‘$HOME’, etc.) are not recognized; use substitute-in-file-name to perform them (see Functions that Expand Filenames). nil in this list refers to default-directory.

Executing a program can also try adding suffixes to the specified name:

User Option: exec-suffixes ¶

This variable is a list of suffixes (strings) to try adding to the specified program file name. The list should include "" if you want the name to be tried exactly as specified. The default value is system-dependent.

Function: exec-suffixes ¶

This function returns the connection-local value of variable exec-suffixes.

Please note: The argument program contains only the name of the program file; it may not contain any command-line arguments. You must use a separate argument, args, to provide those, as described below.

Each of the subprocess-creating functions has a buffer-or-name argument that specifies where the output from the program will go. It should be a buffer or a buffer name; if it is a buffer name, that will create the buffer if it does not already exist. It can also be nil, which says to discard the output, unless a custom filter function handles it. (See Process Filter Functions, and Reading and Printing Lisp Objects.) Normally, you should avoid having multiple processes send output to the same buffer because their output would be intermixed randomly. For synchronous processes, you can send the output to a file instead of a buffer (and the corresponding argument is therefore more appropriately called destination). By default, both standard output and standard error streams go to the same destination, but all the 3 primitives allow optionally to direct the standard error stream to a different destination.

All three of the subprocess-creating functions allow specifying command-line arguments for the process to run. For call-process and call-process-region, these come in the form of a &rest argument, args. For make-process, both the program to run and its command-line arguments are specified as a list of strings. The command-line arguments must all be strings, and they are supplied to the program as separate argument strings. Wildcard characters and other shell constructs have no special meanings in these strings, since the strings are passed directly to the specified program.

The subprocess inherits its environment from Emacs, but you can specify overrides for it with process-environment. See Operating System Environment. The subprocess gets its current directory from the value of default-directory.

Variable: exec-directory ¶

The value of this variable is a string, the name of a directory that contains programs that come with GNU Emacs and are intended for Emacs to invoke. The program movemail is an example of such a program; Rmail uses it to fetch new mail from an inbox.

User Option: exec-path ¶

The value of this variable is a list of directories to search for programs to run in subprocesses. Each element is either the name of a directory (i.e., a string), or nil, which stands for the default directory (which is the value of default-directory). See executable-find, for the details of this search.

The value of exec-path is used by call-process and start-process when the program argument is not an absolute file name.

Generally, you should not modify exec-path directly. Instead, ensure that your PATH environment variable is set appropriately before starting Emacs. Trying to modify exec-path independently of PATH can lead to confusing results.

Function: exec-path ¶

This function is an extension of the variable exec-path. If default-directory indicates a remote directory, this function returns a list of directories used for searching programs on the respective remote host. In case of a local default-directory, the function returns just the value of the variable exec-path. If you use exec-suffixes together with this function, you must also use the function exec-suffixes instead of the variable.

When starting a program that is part of the Emacs distribution, you must take into account that the program may have been renamed in order to comply with executable naming restrictions present on the system.

Instead of starting emacsclient, for example, you should specify the value of emacsclient-program-name instead. Likewise, instead of starting movemail, you must start movemail-program-name, and the same goes for etags, hexl, rcs2log, and ebrowse.

Next: Creating a Synchronous Process, Previous: Functions that Create Subprocesses, Up: Processes   [Contents][Index]

41.2 Shell Arguments ¶

Lisp programs sometimes need to run a shell and give it a command that contains file names that were specified by the user. These programs ought to be able to support any valid file name. But the shell gives special treatment to certain characters, and if these characters occur in the file name, they will confuse the shell. To handle these characters, use the function shell-quote-argument:

Function: shell-quote-argument argument &optional posix ¶

This function returns a string that represents, in shell syntax, an argument whose actual contents are argument. It should work reliably to concatenate the return value into a shell command and then pass it to a shell for execution.

Precisely what this function does depends on your operating system. The function is designed to work with the syntax of your system’s standard shell; if you use an unusual shell, you will need to redefine this function. See Security Considerations.

;; This example shows the behavior on GNU and Unix systems.
(shell-quote-argument "foo > bar")
     ⇒ "foo\\ \\>\\ bar"

;; This example shows the behavior on MS-DOS and MS-Windows.
(shell-quote-argument "foo > bar")
     ⇒ "\"foo > bar\""

Here’s an example of using shell-quote-argument to construct a shell command:

(concat "diff -u "
        (shell-quote-argument oldfile)
        " "
        (shell-quote-argument newfile))

If the optional posix argument is non-nil, argument is quoted according to POSIX shell quoting rules, regardless of the system’s shell. This is useful when your shell could run on a remote host, which requires a POSIX shell in general.

(shell-quote-argument "foo > bar" (file-remote-p default-directory))

The following two functions are useful for combining a list of individual command-line argument strings into a single string, and taking a string apart into a list of individual command-line arguments. These functions are mainly intended for converting user input in the minibuffer, a Lisp string, into a list of string arguments to be passed to make-process, call-process or start-process, or for converting such lists of arguments into a single Lisp string to be presented in the minibuffer or echo area. Note that if a shell is involved (e.g., if using call-process-shell-command), arguments should still be protected by shell-quote-argument; combine-and-quote-strings is not intended to protect special characters from shell evaluation.

Function: split-string-shell-command string ¶

This function splits string into substrings, respecting double and single quotes, as well as backslash quoting.

(split-string-shell-command "ls /tmp/'foo bar'")
     ⇒ ("ls" "/tmp/foo bar")

Function: split-string-and-unquote string &optional separators ¶

This function splits string into substrings at matches for the regular expression separators, like split-string does (see Creating Strings); in addition, it removes quoting from the substrings. It then makes a list of the substrings and returns it.

If separators is omitted or nil, it defaults to "\\s-+", which is a regular expression that matches one or more characters with whitespace syntax (see Table of Syntax Classes).

This function supports two types of quoting: enclosing a whole string in double quotes "…", and quoting individual characters with a backslash escape ‘\’. The latter is also used in Lisp strings, so this function can handle those as well.

Function: combine-and-quote-strings list-of-strings &optional separator ¶

This function concatenates list-of-strings into a single string, quoting each string as necessary. It also sticks the separator string between each pair of strings; if separator is omitted or nil, it defaults to " ". The return value is the resulting string.

The strings in list-of-strings that need quoting are those that include separator as their substring. Quoting a string encloses it in double quotes "…". In the simplest case, if you are consing a command from the individual command-line arguments, every argument that includes embedded blanks will be quoted.

Systems running Emacs impose a limit on the maximum total length of a command and its arguments submitted for execution. If a list of arguments to be processed by an external command might be arbitrarily long, then there is a risk of exceeding this limit, in which case executing the command will fail. In some cases this problem can be avoided by running the command multiple times on subsequent partitions of the list of arguments. When you know that it will not cause problems to run the command more than once, you can use this function to preemptively partition a list of arguments:

Function: multiple-command-partition-arguments command arguments &optional shellp ¶

This function returns a list of subsequent partitions of arguments, a list of strings. command is a string or list of strings specifying the command to be run on arguments (unless shellp is non-nil, see below), and including any arguments that must be passed to every invocation of the command. Then, running a command formed of command plus any one of the returned partitions will not exceed the system’s limits on the maximum total length of a command and its arguments.

If optional argument shellp is non-nil, this function implicitly includes shell-file-name and shell-command-switch at the beginning of command (see Creating an Asynchronous Process). In addition, in that case, this function accounts for the extra length taken up by quoting and space characters in its partitioning calculations.

On systems where the process-environment (see Operating System Environment) counts against command line length limits, this function takes that into account too.

In the following example we impose an artificially small limit on command line length and provide a fixed process-environment for demonstration purposes. The partitioning of the list of arguments into two sublists in the returned value implies that running cmd foo bar baz on this hypothetical system would exceed system limits, and thus fail. The calling code should run cmd twice, on each of the two partitions, so cmd foo bar and then cmd baz.

(let ((system-type 'gnu/linux)
      (command-line-max-length 20)
      (process-environment '("BLAH=blah")))
  (multiple-command-partition-arguments "cmd" '("foo" "bar" "baz")))
     ⇒ (("foo" "bar") ("baz"))

This function takes a conservative approach and does not try to minimize the number of partitions of arguments, because doing that would require a great deal of platform-specific information, and also information about encoding which is not currently made available to Lisp.

Variable: command-line-max-length ¶

This variable holds the maximum length of a command and its arguments on this system, measured in characters, as used by multiple-command-partition-arguments.

Next: Creating an Asynchronous Process, Previous: Shell Arguments, Up: Processes   [Contents][Index]

41.3 Creating a Synchronous Process ¶

After a synchronous process is created, Emacs waits for the process to terminate before continuing. Starting Dired on GNU or Unix³¹ is an example of this: it runs ls in a synchronous process, then modifies the output slightly. Because the process is synchronous, the entire directory listing arrives in the buffer before Emacs tries to do anything with it.

While Emacs waits for the synchronous subprocess to terminate, the user can quit by typing C-g. The first C-g tries to kill the subprocess with a SIGINT signal; but it waits until the subprocess actually terminates before quitting. If during that time the user types another C-g, that kills the subprocess instantly with SIGKILL and quits immediately (except on MS-DOS, where killing other processes doesn’t work). See Quitting.

The synchronous subprocess functions return an indication of how the process terminated.

The output from a synchronous subprocess is generally decoded using a coding system, much like text read from a file. The input sent to a subprocess by call-process-region is encoded using a coding system, much like text written into a file. See Coding Systems.

Function: call-process program &optional infile destination display &rest args ¶

This function calls program and waits for it to finish.

The current working directory of the subprocess is set to the current buffer’s value of default-directory if that is local (as determined by unhandled-file-name-directory), or "~" otherwise. If you want to run a process in a remote directory use process-file.

The standard input for the new process comes from file infile if infile is not nil, and from the null device otherwise. The argument destination says where to put the process output. Here are the possibilities:

a buffer

Insert the output in that buffer, before point. This includes both the standard output stream and the standard error stream of the process.

a buffer name (a string)

Insert the output in a buffer with that name, before point.

t

Insert the output in the current buffer, before point.

nil

Discard the output.

0

Discard the output, and return nil immediately without waiting for the subprocess to finish.

In this case, the process is not truly synchronous, since it can run in parallel with Emacs; but you can think of it as synchronous in that Emacs is essentially finished with the subprocess as soon as this function returns.

MS-DOS doesn’t support asynchronous subprocesses, so this option doesn’t work there.

(:file file-name)

Send the output to the file name specified, overwriting it if it already exists.

(real-destination error-destination)

Keep the standard output stream separate from the standard error stream; deal with the ordinary output as specified by real-destination, and dispose of the error output according to error-destination. If error-destination is nil, that means to discard the error output, t means mix it with the ordinary output, and a string specifies a file name to redirect error output into.

You can’t directly specify a buffer to put the error output in; that is too difficult to implement. But you can achieve this result by sending the error output to a temporary file and then inserting the file into a buffer when the subprocess finishes.

If display is non-nil, then call-process redisplays the buffer as output is inserted. (However, if the coding system chosen for decoding output is undecided, meaning deduce the encoding from the actual data, then redisplay sometimes cannot continue once non-ASCII characters are encountered. There are fundamental reasons why it is hard to fix this; see Receiving Output from Processes.)

Otherwise the function call-process does no redisplay, and the results become visible on the screen only when Emacs redisplays that buffer in the normal course of events.

The remaining arguments, args, are strings that specify command line arguments for the program. Each string is passed to program as a separate argument.

The value returned by call-process (unless you told it not to wait) indicates the reason for process termination. A number gives the exit status of the subprocess; 0 means success, and any other value means failure. If the process terminated with a signal, call-process returns a string describing the signal. If you told call-process not to wait, it returns nil.

In the examples below, the buffer ‘foo’ is current.

(call-process "pwd" nil t)
     ⇒ 0

---------- Buffer: foo ----------
/home/lewis/manual
---------- Buffer: foo ----------

(call-process "grep" nil "bar" nil "lewis" "/etc/passwd")
     ⇒ 0

---------- Buffer: bar ----------
lewis:x:1001:1001:Bil Lewis,,,,:/home/lewis:/bin/bash

---------- Buffer: bar ----------

Here is an example of the use of call-process, as used to be found in the definition of the insert-directory function:

(call-process insert-directory-program nil t nil switches
              (if full-directory-p
                  (concat (file-name-as-directory file) ".")
                file))

Function: process-file program &optional infile buffer display &rest args ¶

This function processes files synchronously in a separate process. It is similar to call-process, but may invoke a file name handler based on the value of the variable default-directory, which specifies the current working directory of the subprocess.

The arguments are handled in almost the same way as for call-process, with the following differences:

Some file name handlers may not support all combinations and forms of the arguments infile, buffer, and display. For example, some file name handlers might behave as if display were nil, regardless of the value actually passed. As another example, some file name handlers might not support separating standard output and error output by way of the buffer argument.

If a file name handler is invoked, it determines the program to run based on the first argument program. For instance, suppose that a handler for remote files is invoked. Then the path that is used for searching for the program might be different from exec-path.

The second argument infile may invoke a file name handler. The file name handler could be different from the handler chosen for the process-file function itself. (For example, default-directory could be on one remote host, and infile on a different remote host. Or default-directory could be non-special, whereas infile is on a remote host.)

If buffer is a list of the form (real-destination error-destination), and error-destination names a file, then the same remarks as for infile apply.

The remaining arguments (args) will be passed to the process verbatim. Emacs is not involved in processing file names that are present in args. To avoid confusion, it may be best to avoid absolute file names in args, but rather to specify all file names as relative to default-directory. The function file-relative-name is useful for constructing such relative file names. Alternatively, you can use file-local-name (see Making Certain File Names “Magic”) to obtain an absolute file name as seen from the remote host’s perspective.

Variable: process-file-side-effects ¶

This variable indicates whether a call of process-file changes remote files.

By default, this variable is always set to t, meaning that a call of process-file could potentially change any file on a remote host. When set to nil, a file name handler could optimize its behavior with respect to remote file attribute caching.

You should only ever change this variable with a let-binding; never with setq.

User Option: process-file-return-signal-string ¶

This user option indicates whether a call of process-file returns a string describing the signal interrupting a remote process.

When a process returns an exit code greater than 128, it is interpreted as a signal. process-file requires returning a string describing this signal.

Since there are processes violating this rule, returning exit codes greater than 128 which are not bound to a signal, process-file returns always the exit code as natural number for remote processes. Setting this user option to non-nil forces process-file to interpret such exit codes as signals, and to return a corresponding string.

Function: call-process-region start end program &optional delete destination display &rest args ¶

This function sends the text from start to end as standard input to a process running program. It deletes the text sent if delete is non-nil; this is useful when destination is t, to insert the output in the current buffer in place of the input.

The arguments destination and display control what to do with the output from the subprocess, and whether to update the display as it comes in. For details, see the description of call-process, above. If destination is the integer 0, call-process-region discards the output and returns nil immediately, without waiting for the subprocess to finish (this only works if asynchronous subprocesses are supported; i.e., not on MS-DOS).

The remaining arguments, args, are strings that specify command line arguments for the program.

The return value of call-process-region is just like that of call-process: nil if you told it to return without waiting; otherwise, a number or string which indicates how the subprocess terminated.

In the following example, we use call-process-region to run the cat utility, with standard input being the first five characters in buffer ‘foo’ (the word ‘input’). cat copies its standard input into its standard output. Since the argument destination is t, this output is inserted in the current buffer.

---------- Buffer: foo ----------
input∗
---------- Buffer: foo ----------

(call-process-region 1 6 "cat" nil t)
     ⇒ 0

---------- Buffer: foo ----------
inputinput∗
---------- Buffer: foo ----------

For example, the shell-command-on-region command uses call-shell-region in a manner similar to this:

(call-shell-region
 start end
 command              ; shell command
 nil                  ; do not delete region
 buffer)              ; send output to buffer

Function: call-process-shell-command command &optional infile destination display ¶

This function executes the shell command command synchronously. The other arguments are handled as in call-process. An old calling convention allowed passing any number of additional arguments after display, which were concatenated to command; this is still supported, but strongly discouraged.

Function: process-file-shell-command command &optional infile destination display ¶

This function is like call-process-shell-command, but uses process-file internally. Depending on default-directory, command can be executed also on remote hosts. An old calling convention allowed passing any number of additional arguments after display, which were concatenated to command; this is still supported, but strongly discouraged.

Function: call-shell-region start end command &optional delete destination ¶

This function sends the text from start to end as standard input to an inferior shell running command. This function is similar than call-process-region, with process being a shell. The arguments delete, destination and the return value are like in call-process-region. Note that this function doesn’t accept additional arguments.

If command names a shell (e.g., via shell-file-name), keep in mind that behavior of various shells when commands are piped to their standard input is shell- and system-dependent, and thus non-portable. The differences are especially prominent when the region includes more than one line, i.e. when piping to a shell commands with embedded newlines. Lisp programs using this technique will therefore need to format the text in the region differently, according to the expectations of the shell.

Function: shell-command-to-string command ¶

This function executes command (a string) as a shell command, then returns the command’s output as a string. If command actually includes more than one command, the behavior depends on the shell to be invoked (determined by shell-file-name for local commands). In particular, the separator between the commands cannot be a newline on MS-Windows; use ‘&&’ instead.

Function: process-lines program &rest args ¶

This function runs program, waits for it to finish, and returns its output as a list of strings. Each string in the list holds a single line of text output by the program; the end-of-line characters are stripped from each line. The arguments beyond program, args, are strings that specify command-line arguments with which to run the program.

If program exits with a non-zero exit status, this function signals an error.

This function works by calling call-process, so program output is decoded in the same way as for call-process.

Function: process-lines-ignore-status program &rest args ¶

This function is just like process-lines, but does not signal an error if program exits with a non-zero exit status.

Next: Deleting Processes, Previous: Creating a Synchronous Process, Up: Processes   [Contents][Index]

41.4 Creating an Asynchronous Process ¶

In this section, we describe how to create an asynchronous process. After an asynchronous process is created, it runs in parallel with Emacs, and Emacs can communicate with it using the functions described in the following sections (see Sending Input to Processes, and see Receiving Output from Processes). Note that process communication is only partially asynchronous: Emacs sends and receives data to and from a process only when those functions are called.

An asynchronous process is controlled either via a pty (pseudo-terminal) or a pipe. The choice of pty or pipe is made when creating the process, by default based on the value of the variable process-connection-type (see below). If available, ptys are usually preferable for processes visible to the user, as in Shell mode, because they allow for job control (C-c, C-z, etc.) between the process and its children, and because interactive programs treat ptys as terminal devices, whereas pipes don’t support these features. However, for subprocesses used by Lisp programs for internal purposes (i.e., no user interaction with the subprocess is required), where significant amounts of data need to be exchanged between the subprocess and the Lisp program, it is often better to use a pipe, because pipes are more efficient. Also, the total number of ptys is limited on many systems, and it is good not to waste them unnecessarily.

Function: make-process &rest args ¶

This function is the basic low-level primitive for starting asynchronous subprocesses. It returns a process object representing the subprocess. Compared to the more high-level start-process, described below, it takes keyword arguments, is more flexible, and enables you to specify process filters and sentinels in a single call.

The arguments args are a list of keyword/argument pairs. Omitting a keyword is always equivalent to specifying it with value nil. Here are the meaningful keywords:

:name name

Use the string name as the process name; if a process with this name already exists, then name is modified (by appending ‘<1>’, etc.) to be unique.

:buffer buffer

Use buffer as the process buffer. If the value is nil, the subprocess is not associated with any buffer.

:command command

Use command as the command line of the process. The value should be a list starting with the program’s executable file name, followed by strings to give to the program as its arguments. If the first element of the list is nil, Emacs opens a new pseudoterminal (pty) and associates its input and output with buffer, without actually running any program; the rest of the list elements are ignored in that case.

:coding coding

If coding is a symbol, it specifies the coding system to be used for both reading and writing of data from and to the connection. If coding is a cons cell (decoding . encoding), then decoding will be used for reading and encoding for writing. The coding system used for encoding the data written to the program is also used for encoding the command-line arguments (but not the program itself, whose file name is encoded as any other file name; see file-name-coding-system).

If coding is nil, the default rules for finding the coding system will apply. See Default Coding Systems.

:connection-type type

Initialize the type of device used to communicate with the subprocess. Possible values are pty to use a pty, pipe to use a pipe, or nil to use the default derived from the value of the process-connection-type variable. If type is a cons cell (input . output), then input will be used for standard input and output for standard output (and standard error if :stderr is nil).

On systems where ptys are not available (MS-Windows), this parameter is ignored, and pipes are used unconditionally.

:noquery query-flag

Initialize the process query flag to query-flag. See Querying Before Exit.

:stop stopped

If provided, stopped must be nil; it is an error to use any non-nil value. The :stop key is ignored otherwise and is retained for compatibility with other process types such as pipe processes. Asynchronous subprocesses never start in the stopped state.

:filter filter

Initialize the process filter to filter. If not specified, a default filter will be provided, which can be overridden later. See Process Filter Functions.

:sentinel sentinel

Initialize the process sentinel to sentinel. If not specified, a default sentinel will be used, which can be overridden later. See Sentinels: Detecting Process Status Changes.

:stderr stderr

Associate stderr with the standard error of the process. A non-nil value should be either a buffer or a pipe process created with make-pipe-process, described below. If stderr is nil, standard error is mixed with standard output, and both are sent to buffer or filter.

If stderr is a buffer, Emacs will create a pipe process, the standard error process. This process will have the default filter (see Process Filter Functions), sentinel (see Sentinels: Detecting Process Status Changes), and coding systems (see Default Coding Systems). On the other hand, it will use query-flag as its query-on-exit flag (see Querying Before Exit). It will be associated with the stderr buffer (see Process Buffers) and send its output (which is the standard error of the main process) there. To get the process object for the standard error process, pass the stderr buffer to get-buffer-process.

If stderr is a pipe process, Emacs will use it as standard error process for the new process.

:file-handler file-handler

If file-handler is non-nil, then look for a file name handler for the current buffer’s default-directory, and invoke that file name handler to make the process. If there is no such handler, proceed as if file-handler were nil.

The original argument list, modified with the actual connection information, is available via the process-contact function.

The current working directory of the subprocess is set to the current buffer’s value of default-directory if that is local (as determined by unhandled-file-name-directory), or ~ otherwise. If you want to run a process in a remote directory, pass :file-handler t to make-process. In that case, the current working directory is the local name component of default-directory (as determined by file-local-name).

Depending on the implementation of the file name handler, it might not be possible to apply filter or sentinel to the resulting process object. The :stderr argument cannot be a pipe process, file name handlers do not support pipe processes for this. A buffer as :stderr argument is accepted, its contents is shown without the use of pipe processes. See Process Filter Functions, Sentinels: Detecting Process Status Changes, and Accepting Output from Processes.

Some file name handlers may not support make-process. In such cases, this function does nothing and returns nil.

Function: make-pipe-process &rest args ¶

This function creates a bidirectional pipe which can be attached to a child process. This is useful with the :stderr keyword of make-process. The function returns a process object.

The arguments args are a list of keyword/argument pairs. Omitting a keyword is always equivalent to specifying it with value nil.

Here are the meaningful keywords:

:name name

Use the string name as the process name. As with make-process, it is modified if necessary to make it unique.

:buffer buffer

Use buffer as the process buffer. If the value is nil, the subprocess is not associated with any buffer.

:coding coding

If coding is a symbol, it specifies the coding system to be used for both reading and writing of data from and to the connection. If coding is a cons cell (decoding . encoding), then decoding will be used for reading and encoding for writing.

If coding is nil, the default rules for finding the coding system will apply. See Default Coding Systems.

:noquery query-flag

Initialize the process query flag to query-flag. See Querying Before Exit.

:stop stopped

If stopped is non-nil, start the process in the stopped state. In the stopped state, a pipe process does not accept incoming data, but you can send outgoing data. The stopped state is set by stop-process and cleared by continue-process (see Sending Signals to Processes).

:filter filter

Initialize the process filter to filter. If not specified, a default filter will be provided, which can be changed later. See Process Filter Functions.

:sentinel sentinel

Initialize the process sentinel to sentinel. If not specified, a default sentinel will be used, which can be changed later. See Sentinels: Detecting Process Status Changes.

The original argument list, modified with the actual connection information, is available via the process-contact function.

Function: start-process name buffer-or-name program &rest args ¶

This function is a higher-level wrapper around make-process, exposing an interface that is similar to call-process. It creates a new asynchronous subprocess and starts the specified program running in it. It returns a process object that stands for the new subprocess in Lisp. The argument name specifies the name for the process object; as with make-process, it is modified if necessary to make it unique. The buffer buffer-or-name is the buffer to associate with the process.

If program is nil, Emacs opens a new pseudoterminal (pty) and associates its input and output with buffer-or-name, without creating a subprocess. In that case, the remaining arguments args are ignored.

The rest of args are strings that specify command line arguments for the subprocess.

In the example below, the first process is started and runs (rather, sleeps) for 100 seconds (the output buffer ‘foo’ is created immediately). Meanwhile, the second process is started, and given the name ‘my-process<1>’ for the sake of uniqueness. It inserts the directory listing at the end of the buffer ‘foo’, before the first process finishes. Then it finishes, and a message to that effect is inserted in the buffer. Much later, the first process finishes, and another message is inserted in the buffer for it.

(start-process "my-process" "foo" "sleep" "100")
     ⇒ #<process my-process>

(start-process "my-process" "foo" "ls" "-l" "/bin")
     ⇒ #<process my-process<1>>

---------- Buffer: foo ----------
total 8336
-rwxr-xr-x 1 root root 971384 Mar 30 10:14 bash
-rwxr-xr-x 1 root root 146920 Jul  5  2011 bsd-csh
...
-rwxr-xr-x 1 root root 696880 Feb 28 15:55 zsh4

Process my-process<1> finished

Process my-process finished
---------- Buffer: foo ----------

Function: start-file-process name buffer-or-name program &rest args ¶

Like start-process, this function starts a new asynchronous subprocess running program in it, and returns its process object.

The difference from start-process is that this function may invoke a file name handler based on the value of default-directory. This handler ought to run program, perhaps on the local host, perhaps on a remote host that corresponds to default-directory. In the latter case, the local part of default-directory becomes the working directory of the process.

This function does not try to invoke file name handlers for program or for the rest of args. For that reason, if program or any of args use the remote-file syntax (see Making Certain File Names “Magic”), they must be converted either to file names relative to default-directory, or to names that identify the files locally on the remote host, by running them through file-local-name.

Depending on the implementation of the file name handler, it might not be possible to apply process-filter or process-sentinel to the resulting process object. See Process Filter Functions, and Sentinels: Detecting Process Status Changes.

Some file name handlers may not support start-file-process (for example the function ange-ftp-hook-function). In such cases, this function does nothing and returns nil.

Function: start-process-shell-command name buffer-or-name command ¶

This function is like start-process, except that it uses a shell to execute the specified command. The argument command is a shell command string. The variable shell-file-name specifies which shell to use.

The point of running a program through the shell, rather than directly with make-process or start-process, is so that you can employ shell features such as wildcards in the arguments. It follows that if you include any arbitrary user-specified arguments in the command, you should quote them with shell-quote-argument first, so that any special shell characters do not have their special shell meanings. See Shell Arguments. Of course, when executing commands based on user input you should also consider the security implications.

Function: start-file-process-shell-command name buffer-or-name command ¶

This function is like start-process-shell-command, but uses start-file-process internally. Because of this, command can also be executed on remote hosts, depending on default-directory.

Variable: process-connection-type ¶

This variable controls the type of device used to communicate with asynchronous subprocesses. If it is non-nil, then ptys are used, when available. Otherwise, pipes are used.

The value of process-connection-type takes effect when make-process or start-process is called. So you can specify how to communicate with one subprocess by binding the variable around the call to these functions.

Note that the value of this variable is ignored when make-process is called with a non-nil value of the :stderr parameter; in that case, Emacs will communicate with the process using pipes. It is also ignored if ptys are unavailable (MS-Windows).

(let ((process-connection-type nil))  ; use a pipe
  (start-process ...))

To determine whether a given subprocess actually got a pipe or a pty, use the function process-tty-name (see Process Information).

Variable: process-error-pause-time ¶

If a process sentinel/filter function has an error, Emacs will (by default) pause Emacs for process-error-pause-time seconds after displaying this error, so that users will see the error in question. However, this can lead to situations where Emacs becomes unresponsive (if there’s a lot of these errors happening), so this can be disabled by setting process-error-pause-time to 0.

Next: Process Information, Previous: Creating an Asynchronous Process, Up: Processes   [Contents][Index]

41.5 Deleting Processes ¶

Deleting a process disconnects Emacs immediately from the subprocess. Processes are deleted automatically after they terminate, but not necessarily right away. You can delete a process explicitly at any time. If you explicitly delete a terminated process before it is deleted automatically, no harm results. Deleting a running process sends a signal to terminate it (and its child processes, if any), and calls the process sentinel. See Sentinels: Detecting Process Status Changes.

When a process is deleted, the process object itself continues to exist as long as other Lisp objects point to it. All the Lisp primitives that work on process objects accept deleted processes, but those that do I/O or send signals will report an error. The process mark continues to point to the same place as before, usually into a buffer where output from the process was being inserted.

User Option: delete-exited-processes ¶

This variable controls automatic deletion of processes that have terminated (due to calling exit or to a signal). If it is nil, then they continue to exist until the user runs list-processes. Otherwise, they are deleted immediately after they exit.

Function: delete-process &optional process ¶

This function deletes a process, killing it with a SIGKILL signal if the process was running a program. The argument may be a process, the name of a process, a buffer, or the name of a buffer. (A buffer or buffer-name stands for the process that get-buffer-process returns, and a missing or nil process means that the current buffer’s process should be killed.) Calling delete-process on a running process terminates it, updates the process status, and runs the sentinel immediately. If the process has already terminated, calling delete-process has no effect on its status, or on the running of its sentinel (which will happen sooner or later).

If the process object represents a network, serial, or pipe connection, its status changes to closed; otherwise, it changes to signal, unless the process already exited. See process-status.

(delete-process "*shell*")
     ⇒ nil

Next: Sending Input to Processes, Previous: Deleting Processes, Up: Processes   [Contents][Index]

41.6 Process Information ¶

Several functions return information about processes.

Command: list-processes &optional query-only buffer ¶

This command displays a listing of all living processes. In addition, it finally deletes any process whose status was ‘Exited’ or ‘Signaled’. It returns nil.

The processes are shown in a buffer named *Process List* (unless you specify otherwise using the optional argument buffer), whose major mode is Process Menu mode.

If query-only is non-nil, it only lists processes whose query flag is non-nil. See Querying Before Exit.

Function: process-list ¶

This function returns a list of all processes that have not been deleted.

(process-list)
     ⇒ (#<process display-time> #<process shell>)

Function: num-processors &optional query ¶

This function returns the number of processors, a positive integer. Each usable thread execution unit counts as a processor. By default, the count includes the number of available processors, which you can override by setting the OMP_NUM_THREADS environment variable of OpenMP. If the optional argument query is current, this function ignores OMP_NUM_THREADS; if query is all, this function also counts processors that are on the system but are not available to the current process.

Function: get-process name ¶

This function returns the process named name (a string), or nil if there is none. The argument name can also be a process object, in which case it is returned.

(get-process "shell")
     ⇒ #<process shell>

Function: process-command process ¶

This function returns the command that was executed to start process. This is a list of strings, the first string being the program executed and the rest of the strings being the arguments that were given to the program. For a network, serial, or pipe connection, this is either nil, which means the process is running or t (process is stopped).

(process-command (get-process "shell"))
     ⇒ ("bash" "-i")

Function: process-contact process &optional key no-block ¶

This function returns information about how a network, a serial, or a pipe connection was set up. When key is nil, it returns (hostname service) for a network connection, (port speed) for a serial connection, and t for a pipe connection. For an ordinary child process, this function always returns t when called with a nil key.

If key is t, the value is the complete status information for the connection, server, serial port, or pipe; that is, the list of keywords and values specified in make-network-process, make-serial-process, or make-pipe-process, except that some of the values represent the current status instead of what you specified.

For a network process, the values include (see make-network-process for a complete list):

:buffer

The associated value is the process buffer.

:filter

The associated value is the process filter function. See Process Filter Functions.

:sentinel

The associated value is the process sentinel function. See Sentinels: Detecting Process Status Changes.

:remote

In a connection, the address in internal format of the remote peer.

:local

The local address, in internal format.

:service

In a server, if you specified t for service, this value is the actual port number.

:local and :remote are included even if they were not specified explicitly in make-network-process.

For a serial connection, see make-serial-process and serial-process-configure for the list of keys. For a pipe connection, see make-pipe-process for the list of keys.

If key is a keyword, the function returns the value corresponding to that keyword.

If process is a non-blocking network stream that hasn’t been fully set up yet, then this function will block until that has happened. If given the optional no-block parameter, this function will return nil instead of blocking.

Function: process-id process ¶

This function returns the PID of process. This is an integral number that distinguishes the process process from all other processes running on the same computer at the current time. The PID of a process is chosen by the operating system kernel when the process is started and remains constant as long as the process exists. For network, serial, and pipe connections, this function returns nil.

Function: process-name process ¶

This function returns the name of process, as a string.

Function: process-status process-name ¶

This function returns the status of process-name as a symbol. The argument process-name must be a process, a buffer, or a process name (a string).

The possible values for an actual subprocess are:

run

for a process that is running.

stop

for a process that is stopped but continuable.

exit

for a process that has exited.

signal

for a process that has received a fatal signal.

open

for a network, serial, or pipe connection that is open.

closed

for a network, serial, or pipe connection that is closed. Once a connection is closed, you cannot reopen it, though you might be able to open a new connection to the same place.

connect

for a non-blocking connection that is waiting to complete.

failed

for a non-blocking connection that has failed to complete.

listen

for a network server that is listening.

nil

if process-name is not the name of an existing process.

(process-status (get-buffer "*shell*"))
     ⇒ run

For a network, serial, or pipe connection, process-status returns one of the symbols open, stop, or closed. The latter means that the other side closed the connection, or Emacs did delete-process. The value stop means that stop-process was called on the connection.

Function: process-live-p process ¶

This function returns non-nil if process is alive. A process is considered alive if its status is run, open, listen, connect or stop.

Function: process-type process ¶

This function returns the symbol network for a network connection or server, serial for a serial port connection, pipe for a pipe connection, or real for a subprocess created for running a program.

Function: process-exit-status process ¶

This function returns the exit status of process or the signal number that killed it. (Use the result of process-status to determine which of those it is.) If process has not yet terminated, the value is 0. For network, serial, and pipe connections that are already closed, the value is either 0 or 256, depending on whether the connection was closed normally or abnormally.

Function: process-tty-name process &optional stream ¶

This function returns the terminal name that process is using for its communication with Emacs—or nil if it is using pipes instead of a pty (see process-connection-type in Creating an Asynchronous Process). By default, this function returns the terminal name if any of process’s standard streams use a terminal. If stream is one of stdin, stdout, or stderr, this function returns the terminal name (or nil, as above) that process uses for that stream specifically. You can use this to determine whether a particular stream uses a pipe or a pty.

If process represents a program running on a remote host, this function returns the local terminal name that communicates with process; you can get the terminal name used by that program on the remote host with the process property remote-tty. If process represents a network, serial, or pipe connection, this function always returns nil.

Function: process-coding-system process ¶

This function returns a cons cell (decode . encode), describing the coding systems in use for decoding output from, and encoding input to, process (see Coding Systems).

Function: set-process-coding-system process &optional decoding-system encoding-system ¶

This function specifies the coding systems to use for subsequent output from and input to process. It will use decoding-system to decode subprocess output, and encoding-system to encode subprocess input.

Every process also has a property list that you can use to store miscellaneous values associated with the process.

Function: process-get process propname ¶

This function returns the value of the propname property of process.

Function: process-put process propname value ¶

This function sets the value of the propname property of process to value.

Function: process-plist process ¶

This function returns the process plist of process.

Function: set-process-plist process plist ¶

This function sets the process plist of process to plist.

Next: Sending Signals to Processes, Previous: Process Information, Up: Processes   [Contents][Index]

41.7 Sending Input to Processes ¶

Asynchronous subprocesses receive input when it is sent to them by Emacs, which is done with the functions in this section. You must specify the process to send input to, and the input data to send. If the subprocess runs a program, the data appears on the standard input of that program; for connections, the data is sent to the connected device or program.

Some operating systems have limited space for buffered input in a pty. On these systems, Emacs sends an EOF periodically amidst the other characters, to force them through. For most programs, these EOFs do no harm.

Subprocess input is normally encoded using a coding system before the subprocess receives it, much like text written into a file. You can use set-process-coding-system to specify which coding system to use (see Process Information). Otherwise, the coding system comes from coding-system-for-write, if that is non-nil; or else from the defaulting mechanism (see Default Coding Systems).

Sometimes the system is unable to accept input for that process, because the input buffer is full. When this happens, the send functions wait a short while, accepting output from subprocesses, and then try again. This gives the subprocess a chance to read more of its pending input and make space in the buffer. It also allows filters (including the one currently running), sentinels and timers to run—so take account of that in writing your code.

In these functions, the process argument can be a process or the name of a process, or a buffer or buffer name (which stands for a process via get-buffer-process). nil means the current buffer’s process.

Function: process-send-string process string ¶

This function sends process the contents of string as standard input. It returns nil. For example, to make a Shell buffer list files:

(process-send-string "shell<1>" "ls\n")
     ⇒ nil

Function: process-send-region process start end ¶

This function sends the text in the region defined by start and end as standard input to process.

An error is signaled unless both start and end are integers or markers that indicate positions in the current buffer. (It is unimportant which number is larger.)

Function: process-send-eof &optional process ¶

This function makes process see an end-of-file in its input. The EOF comes after any text already sent to it. The function returns process.

(process-send-eof "shell")
     ⇒ "shell"

Function: process-running-child-p &optional process ¶

This function will tell you whether a process, which must not be a connection but a real subprocess, has given control of its terminal to a child process of its own. If this is true, the function returns the numeric ID of the foreground process group of process; it returns nil if Emacs can be certain that this is not so. The value is t if Emacs cannot tell whether this is true. This function signals an error if process is a network, serial, or pipe connection, or if the subprocess is not active.

Next: Receiving Output from Processes, Previous: Sending Input to Processes, Up: Processes   [Contents][Index]

41.8 Sending Signals to Processes ¶

Sending a signal to a subprocess is a way of interrupting its activities. There are several different signals, each with its own meaning. The set of signals and their names is defined by the operating system. For example, the signal SIGINT means that the user has typed C-c, or that some analogous thing has happened.

Each signal has a standard effect on the subprocess. Most signals kill the subprocess, but some stop (or resume) execution instead. Most signals can optionally be handled by programs; if the program handles the signal, then we can say nothing in general about its effects.

You can send signals explicitly by calling the functions in this section. Emacs also sends signals automatically at certain times: killing a buffer sends a SIGHUP signal to all its associated processes; killing Emacs sends a SIGHUP signal to all remaining processes. (SIGHUP is a signal that usually indicates that the user “hung up the phone”, i.e., disconnected.)

Each of the signal-sending functions takes two optional arguments: process and current-group.

The argument process must be either a process, a process name, a buffer, a buffer name, or nil. A buffer or buffer name stands for a process through get-buffer-process. nil stands for the process associated with the current buffer. Except with stop-process and continue-process, an error is signaled if process does not identify an active process, or if it represents a network, serial, or pipe connection.

The argument current-group is a flag that makes a difference when you are running a job-control shell as an Emacs subprocess. If it is non-nil, then the signal is sent to the current process-group of the terminal that Emacs uses to communicate with the subprocess. If the process is a job-control shell, this means the shell’s current subjob. If current-group is nil, the signal is sent to the process group of the immediate subprocess of Emacs. If the subprocess is a job-control shell, this is the shell itself. If current-group is lambda, the signal is sent to the process-group that owns the terminal, but only if it is not the shell itself.

The flag current-group has no effect when a pipe is used to communicate with the subprocess, because the operating system does not support the distinction in the case of pipes. For the same reason, job-control shells won’t work when a pipe is used. See process-connection-type in Creating an Asynchronous Process.

Function: interrupt-process &optional process current-group ¶

This function interrupts the process process by sending the signal SIGINT. Outside of Emacs, typing the interrupt character (normally C-c on some systems, and DEL on others) sends this signal. When the argument current-group is non-nil, you can think of this function as typing C-c on the terminal by which Emacs talks to the subprocess.

Command: kill-process &optional process current-group ¶

This command kills the process process by sending the signal SIGKILL. This signal kills the subprocess immediately, and cannot be handled by the subprocess. Interactively, it’ll prompt the user for a process name, defaulting to the process (if any) in the current buffer.

Function: quit-process &optional process current-group ¶

This function sends the signal SIGQUIT to the process process. This signal is the one sent by the quit character (usually C-\) when you are not inside Emacs.

Function: stop-process &optional process current-group ¶

This function stops the specified process. If it is a real subprocess running a program, it sends the signal SIGTSTP to that subprocess. If process represents a network, serial, or pipe connection, this function inhibits handling of the incoming data from the connection; for a network server, this means not accepting new connections. Use continue-process to resume normal execution.

Outside of Emacs, on systems with job control, the stop character (usually C-z) normally sends the SIGTSTP signal to a subprocess. When current-group is non-nil, you can think of this function as typing C-z on the terminal Emacs uses to communicate with the subprocess.

Function: continue-process &optional process current-group ¶

This function resumes execution of the process process. If it is a real subprocess running a program, it sends the signal SIGCONT to that subprocess; this presumes that process was stopped previously. If process represents a network, serial, or pipe connection, this function resumes handling of the incoming data from the connection. For serial connections, data that arrived during the time the process was stopped might be lost.

Command: signal-process process signal &optional remote ¶

This function sends a signal to process process. The argument signal specifies which signal to send; it should be an integer, or a symbol whose name is a signal.

The process argument can be a system process ID (an integer); that allows you to send signals to processes that are not children of Emacs. See Accessing Other Processes.

If process is a process object which contains the property remote-pid, or process is a number and remote is a remote file name, process is interpreted as process on the respective remote host, which will be the process to signal.

If process is a string, it is interpreted as process object with the respective process name, or as a number.

Sometimes, it is necessary to send a signal to a non-local asynchronous process. This is possible by writing an own interrupt-process or signal-process implementation. This function must be added then to interrupt-process-functions or signal-process-functions, respectively.

Variable: interrupt-process-functions ¶

This variable is a list of functions to be called for interrupt-process. The arguments of the functions are the same as for interrupt-process. These functions are called in the order of the list, until one of them returns non-nil. The default function, which shall always be the last in this list, is internal-default-interrupt-process.

This is the mechanism, how Tramp implements interrupt-process.

Variable: signal-process-functions ¶

This variable is a list of functions to be called for signal-process. The arguments of the functions are the same as for signal-process. These functions are called in the order of the list, until one of them returns non-nil. The default function, which shall always be the last in this list, is internal-default-signal-process.

This is the mechanism, how Tramp implements signal-process.

Next: Sentinels: Detecting Process Status Changes, Previous: Sending Signals to Processes, Up: Processes   [Contents][Index]

41.9 Receiving Output from Processes ¶

The output that an asynchronous subprocess writes to its standard output stream is passed to a function called the filter function. The default filter function simply inserts the output into a buffer, which is called the associated buffer of the process (see Process Buffers). If the process has no buffer then the default filter discards the output.

If the subprocess writes to its standard error stream, by default the error output is also passed to the process filter function. Alternatively, you could use the :stderr parameter with a non-nil value in a call to make-process (see make-process) to make the destination of the error output separate from the standard output.

When a subprocess terminates, Emacs reads any pending output, then stops reading output from that subprocess. Therefore, if the subprocess has children that are still live and still producing output, Emacs won’t receive that output.

Output from a subprocess can arrive only while Emacs is waiting: when reading terminal input (see the function waiting-for-user-input-p), in sit-for and sleep-for (see Waiting for Elapsed Time or Input), in accept-process-output (see Accepting Output from Processes), and in functions which send data to processes (see Sending Input to Processes). This minimizes the problem of timing errors that usually plague parallel programming. For example, you can safely create a process and only then specify its buffer or filter function; no output can arrive before you finish, if the code in between does not call any primitive that waits.

Variable: process-adaptive-read-buffering ¶

On some systems, when Emacs reads the output from a subprocess, the output data is read in very small blocks, potentially resulting in very poor performance. This behavior can be remedied to some extent by setting the variable process-adaptive-read-buffering to a non-nil value, as it will automatically delay reading from such processes, thus allowing them to produce more output before Emacs tries to read it. The default is nil, since a non-nil value reduces performance.

• Process Buffers
• Process Filter Functions
• Decoding Process Output
• Accepting Output from Processes
• Processes and Threads

(defun ordinary-insertion-filter (proc string)
  (when (buffer-live-p (process-buffer proc))
    (with-current-buffer (process-buffer proc)
      (let ((moving (= (point) (process-mark proc))))

        (save-excursion
          ;; Insert the text, advancing the process marker.
          (goto-char (process-mark proc))
          (insert string)
          (set-marker (process-mark proc) (point)))
        (if moving (goto-char (process-mark proc)))))))

(display-buffer (process-buffer proc))

(defun keep-output (process output)
   (setq kept (cons output kept)))
     ⇒ keep-output

(setq kept nil)
     ⇒ nil

(set-process-filter (get-process "shell") 'keep-output)
     ⇒ keep-output

(process-send-string "shell" "ls ~/other\n")
     ⇒ nil
kept
     ⇒ ("lewis@slug:$ "

"FINAL-W87-SHORT.MSS    backup.otl              kolstad.mss~
address.txt             backup.psf              kolstad.psf
backup.bib~             david.mss               resume-Dec-86.mss~
backup.err              david.psf               resume-Dec.psf
backup.mss              dland                   syllabus.mss
"
"#backups.mss#          backup.mss~             kolstad.mss
")

;; This loop contains a bug.
(while (process-live-p process)
  (accept-process-output process))

(while (accept-process-output process))

(while (accept-process-output process))
(while (accept-process-output stderr-process))

(let* ((stdout (generate-new-buffer "stdout"))
       (stderr (generate-new-buffer "stderr"))
       (process (make-process :name "test"
                              :command '("my-program")
                              :buffer stdout
                              :stderr stderr))
       (stderr-process (get-buffer-process stderr)))
  (unless (and process stderr-process)
    (error "Process unexpectedly nil"))
  (while (accept-process-output process))
  (while (accept-process-output stderr-process)))

Next: Querying Before Exit, Previous: Receiving Output from Processes, Up: Processes   [Contents][Index]

41.10 Sentinels: Detecting Process Status Changes ¶

A process sentinel is a function that is called whenever the associated process changes status for any reason, including signals (whether sent by Emacs or caused by the process’s own actions) that terminate, stop, or continue the process. The process sentinel is also called if the process exits. The sentinel receives two arguments: the process for which the event occurred, and a string describing the type of event.

If no sentinel function was specified for a process, it will use the default sentinel function, which inserts a message in the process’s buffer with the process name and the string describing the event.

The string describing the event looks like one of the following (but this is not an exhaustive list of event strings):

• "finished\n".
• "deleted\n".
• "exited abnormally with code exitcode (core dumped)\n". The “core dumped” part is optional, and only appears if the process dumped core.
• "failed with code fail-code\n".
• "signal-description (core dumped)\n". The signal-description is a system-dependent textual description of a signal, e.g., "killed" for SIGKILL. The “core dumped” part is optional, and only appears if the process dumped core.
• "open from host-name\n".
• "open\n".
• "run\n".
• "connection broken by remote peer\n".

A sentinel runs only while Emacs is waiting (e.g., for terminal input, or for time to elapse, or for process output). This avoids the timing errors that could result from running sentinels at random places in the middle of other Lisp programs. A program can wait, so that sentinels will run, by calling sit-for or sleep-for (see Waiting for Elapsed Time or Input), or accept-process-output (see Accepting Output from Processes). Emacs also allows sentinels to run when the command loop is reading input. delete-process calls the sentinel when it terminates a running process.

Emacs does not keep a queue of multiple reasons to call the sentinel of one process; it records just the current status and the fact that there has been a change. Therefore two changes in status, coming in quick succession, can call the sentinel just once. However, process termination will always run the sentinel exactly once. This is because the process status can’t change again after termination.

Emacs explicitly checks for output from the process before running the process sentinel. Once the sentinel runs due to process termination, no further output can arrive from the process.

A sentinel that writes the output into the buffer of the process should check whether the buffer is still alive. If it tries to insert into a dead buffer, it will get an error. If the buffer is dead, (buffer-name (process-buffer process)) returns nil.

Quitting is normally inhibited within a sentinel—otherwise, the effect of typing C-g at command level or to quit a user command would be unpredictable. If you want to permit quitting inside a sentinel, bind inhibit-quit to nil. In most cases, the right way to do this is with the macro with-local-quit. See Quitting.

If an error happens during execution of a sentinel, it is caught automatically, so that it doesn’t stop the execution of whatever programs was running when the sentinel was started. However, if debug-on-error is non-nil, errors are not caught. This makes it possible to use the Lisp debugger to debug the sentinel. See The Lisp Debugger. If an error is caught, Emacs pauses for process-error-pause-time seconds so that the user sees the error. See Creating an Asynchronous Process.

While a sentinel is running, the process sentinel is temporarily set to nil so that the sentinel won’t run recursively. For this reason it is not possible for a sentinel to specify a new sentinel.

Note that Emacs automatically saves and restores the match data while executing sentinels. See The Match Data.

Function: set-process-sentinel process sentinel ¶

This function associates sentinel with process. If sentinel is nil, then the process will have the default sentinel, which inserts a message in the process’s buffer when the process status changes.

Changes in process sentinels take effect immediately—if the sentinel is slated to be run but has not been called yet, and you specify a new sentinel, the eventual call to the sentinel will use the new one.

(defun msg-me (process event)
   (princ
     (format "Process: %s had the event '%s'" process event)))
(set-process-sentinel (get-process "shell") 'msg-me)
     ⇒ msg-me

(kill-process (get-process "shell"))
     ⊣ Process: #<process shell> had the event 'killed'
     ⇒ #<process shell>

Function: process-sentinel process ¶

This function returns the sentinel of process.

In case a process status changes need to be passed to several sentinels, you can use add-function to combine an existing sentinel with a new one. See Advising Emacs Lisp Functions.

Function: waiting-for-user-input-p ¶

While a sentinel or filter function is running, this function returns non-nil if Emacs was waiting for keyboard input from the user at the time the sentinel or filter function was called, or nil if it was not.

Next: Accessing Other Processes, Previous: Sentinels: Detecting Process Status Changes, Up: Processes   [Contents][Index]

41.11 Querying Before Exit ¶

When Emacs exits, it terminates all its subprocesses. For subprocesses that run a program, it sends them the SIGHUP signal; connections are simply closed. Because subprocesses may be doing valuable work, Emacs normally asks the user to confirm that it is ok to terminate them. Each process has a query flag, which, if non-nil, says that Emacs should ask for confirmation before exiting and thus killing that process. The default for the query flag is t, meaning do query.

Function: process-query-on-exit-flag process ¶

This returns the query flag of process.

Function: set-process-query-on-exit-flag process flag ¶

This function sets the query flag of process to flag. It returns flag.

Here is an example of using set-process-query-on-exit-flag on a shell process to avoid querying:

(set-process-query-on-exit-flag (get-process "shell") nil)
     ⇒ nil

User Option: confirm-kill-processes ¶

If this user option is set to t (the default), then Emacs asks for confirmation before killing processes on exit. If it is nil, Emacs kills processes without confirmation, i.e., the query flag of all processes is ignored.

Next: Transaction Queues, Previous: Querying Before Exit, Up: Processes   [Contents][Index]

41.12 Accessing Other Processes ¶

In addition to accessing and manipulating processes that are subprocesses of the current Emacs session, Emacs Lisp programs can also access other processes. We call these system processes, to distinguish them from Emacs subprocesses.

Emacs provides several primitives for accessing system processes. Not all platforms support these primitives; on those which don’t, these primitives return nil.

Function: list-system-processes ¶

This function returns a list of all the processes running on the system. Each process is identified by its PID, a numerical process ID that is assigned by the OS and distinguishes the process from all the other processes running on the same machine at the same time.

If default-directory points to a remote host, processes of that host are returned.

Function: process-attributes pid ¶

This function returns an alist of attributes for the process specified by its process ID pid. Each association in the alist is of the form (key . value), where key designates the attribute and value is the value of that attribute. The various attribute keys that this function can return are listed below. Not all platforms support all of these attributes; if an attribute is not supported, its association will not appear in the returned alist.

If default-directory points to a remote host, pid is regarded as process of that host.

euid

The effective user ID of the user who invoked the process. The corresponding value is a number. If the process was invoked by the same user who runs the current Emacs session, the value is identical to what user-uid returns (see User Identification).

user

User name corresponding to the process’s effective user ID, a string.

egid

The group ID of the effective user ID, a number.

group

Group name corresponding to the effective user’s group ID, a string.

comm

The name of the command that runs in the process. This is a string that usually specifies the name of the executable file of the process, without the leading directories. However, some special system processes can report strings that do not correspond to an executable file of a program.

state

The state code of the process. This is a short string that encodes the scheduling state of the process. Here’s a list of the most frequently seen codes:

"D"

uninterruptible sleep (usually I/O)

"R"

running

"S"

interruptible sleep (waiting for some event)

"T"

stopped, e.g., by a job control signal

"Z"

zombie: a process that terminated, but was not reaped by its parent

For the full list of the possible states, see the manual page of the ps command.

ppid

The process ID of the parent process, a number.

pgrp

The process group ID of the process, a number.

sess

The session ID of the process. This is a number that is the process ID of the process’s session leader.

ttname

A string that is the name of the process’s controlling terminal. On Unix and GNU systems, this is normally the file name of the corresponding terminal device, such as /dev/pts65.

tpgid

The numerical process group ID of the foreground process group that uses the process’s terminal.

minflt

The number of minor page faults caused by the process since its beginning. (Minor page faults are those that don’t involve reading from disk.)

majflt

The number of major page faults caused by the process since its beginning. (Major page faults require a disk to be read, and are thus more expensive than minor page faults.)

cminflt

cmajflt

Like minflt and majflt, but include the number of page faults for all the child processes of the given process.

utime

Time spent by the process in the user context, for running the application’s code. The corresponding value is a Lisp timestamp (see Time of Day).

stime

Time spent by the process in the system (kernel) context, for processing system calls. The corresponding value is a Lisp timestamp.

time

The sum of utime and stime. The corresponding value is a Lisp timestamp.

cutime

cstime

ctime

Like utime, stime, and time, but include the times of all the child processes of the given process.

pri

The numerical priority of the process.

nice

The nice value of the process, a number. (Processes with smaller nice values get scheduled more favorably.)

thcount

The number of threads in the process.

start

The time when the process was started, as a Lisp timestamp.

etime

The time elapsed since the process started, as a Lisp timestamp.

vsize

The virtual memory size of the process, measured in kilobytes.

rss

The size of the process’s resident set, the number of kilobytes occupied by the process in the machine’s physical memory.

pcpu

The percentage of the CPU time used by the process since it started. The corresponding value is a nonnegative floating-point number. Although in theory the number can exceed 100 on a multicore platform, it is usually less than 100 because Emacs is typically single-threaded.

pmem

The percentage of the total physical memory installed on the machine used by the process’s resident set. The value is a floating-point number between 0 and 100.

args

The command-line with which the process was invoked. This is a string in which individual command-line arguments are separated by blanks; whitespace characters that are embedded in the arguments are quoted as appropriate for the system’s shell: escaped by backslash characters on GNU and Unix, and enclosed in double quote characters on Windows. Thus, this command-line string can be directly used in primitives such as shell-command.

Next: Network Connections, Previous: Accessing Other Processes, Up: Processes   [Contents][Index]

41.13 Transaction Queues ¶

You can use a transaction queue to communicate with a subprocess using transactions. First use tq-create to create a transaction queue communicating with a specified process. Then you can call tq-enqueue to send a transaction.

Function: tq-create process ¶

This function creates and returns a transaction queue communicating with process. The argument process should be a subprocess capable of sending and receiving streams of bytes. It may be a child process, or it may be a TCP connection to a server, possibly on another machine.

Function: tq-enqueue queue question regexp closure fn &optional delay-question ¶

This function sends a transaction to queue queue. Specifying the queue has the effect of specifying the subprocess to talk to.

The argument question is the outgoing message that starts the transaction. The argument fn is the function to call when the corresponding answer comes back; it is called with two arguments: closure, and the answer received.

The argument regexp is a regular expression that should match text at the end of the entire answer, but nothing before; that’s how tq-enqueue determines where the answer ends.

If the argument delay-question is non-nil, delay sending this question until the process has finished replying to any previous questions. This produces more reliable results with some processes.

Function: tq-close queue ¶

Shut down transaction queue queue, waiting for all pending transactions to complete, and then terminate the connection or child process.

Transaction queues are implemented by means of a filter function. See Process Filter Functions.

Next: Network Servers, Previous: Transaction Queues, Up: Processes   [Contents][Index]

41.14 Network Connections ¶

Emacs Lisp programs can open stream (TCP) and datagram (UDP) network connections (see Datagrams) to other processes on the same machine or other machines. A network connection is handled by Lisp much like a subprocess, and is represented by a process object. However, the process you are communicating with is not a child of the Emacs process, has no process ID, and you can’t kill it or send it signals. All you can do is send and receive data. delete-process closes the connection, but does not kill the program at the other end; that program must decide what to do about closure of the connection.

Lisp programs can listen for connections by creating network servers. A network server is also represented by a kind of process object, but unlike a network connection, the network server never transfers data itself. When it receives a connection request, it creates a new network connection to represent the connection just made. (The network connection inherits certain information, including the process plist, from the server.) The network server then goes back to listening for more connection requests.

Network connections and servers are created by calling make-network-process with an argument list consisting of keyword/argument pairs, for example :server t to create a server process, or :type 'datagram to create a datagram connection. See Low-Level Network Access, for details. You can also use the open-network-stream function described below.

To distinguish the different types of processes, the process-type function returns the symbol network for a network connection or server, serial for a serial port connection, pipe for a pipe connection, or real for a real subprocess.

The process-status function returns open, closed, connect, stop, or failed for network connections. For a network server, the status is always listen. Except for stop, none of those values is possible for a real subprocess. See Process Information.

You can stop and resume operation of a network process by calling stop-process and continue-process. For a server process, being stopped means not accepting new connections. (Up to 5 connection requests will be queued for when you resume the server; you can increase this limit, unless it is imposed by the operating system—see the :server keyword of make-network-process, make-network-process.) For a network stream connection, being stopped means not processing input (any arriving input waits until you resume the connection). For a datagram connection, some number of packets may be queued but input may be lost. You can use the function process-command to determine whether a network connection or server is stopped; a non-nil value means yes.

Emacs can create encrypted network connections, using the built-in support for the GnuTLS Transport Layer Security Library; see the GnuTLS project page. If your Emacs was compiled with GnuTLS support, the function gnutls-available-p is defined and returns non-nil. For more details, see Overview in The Emacs-GnuTLS manual. The open-network-stream function can transparently handle the details of creating encrypted connections for you, using whatever support is available.

Function: open-network-stream name buffer host service &rest parameters ¶

This function opens a TCP connection, with optional encryption, and returns a process object that represents the connection.

The name argument specifies the name for the process object. It is modified as necessary to make it unique.

The buffer argument is the buffer to associate with the connection. Output from the connection is inserted in the buffer, unless you specify your own filter function to handle the output. If buffer is nil, it means that the connection is not associated with any buffer.

The arguments host and service specify where to connect to; host is the host name (a string), and service is the name of a defined network service (a string) or a port number (an integer like 80 or an integer string like "80").

The remaining arguments parameters are keyword/argument pairs that are mainly relevant to encrypted connections:

:nowait boolean

If non-nil, try to make an asynchronous connection.

:noquery query-flag

Initialize the process query flag to query-flag. See Querying Before Exit.

:coding coding

Use this to set the coding systems used by the network process, in preference to binding coding-system-for-read or coding-system-for-write. See make-network-process, for details.

:type type

The type of connection. Options are:

plain

An ordinary, unencrypted connection.

tls

ssl

A TLS (Transport Layer Security) connection.

nil

network

Start with a plain connection, and if parameters ‘:success’ and ‘:capability-command’ are supplied, try to upgrade to an encrypted connection via STARTTLS. If that fails, retain the unencrypted connection.

starttls

As for nil, but if STARTTLS fails, drop the connection.

shell

A shell connection.

:always-query-capabilities boolean

If non-nil, always ask for the server’s capabilities, even when doing a ‘plain’ connection.

:capability-command capability-command

Command to query the host capabilities. This can either be a string (which will then be sent verbatim to the server) or a function (called with a single parameter: the “greeting” from the server when connecting) that should return a string.

:end-of-command regexp

:end-of-capability regexp

Regular expression matching the end of a command, or the end of the command capability-command. The latter defaults to the former.

:starttls-function function

Function of one argument (the response to capability-command), which returns either nil or the command to activate STARTTLS, if supported.

:success regexp

Regular expression matching a successful STARTTLS negotiation.

:use-starttls-if-possible boolean

If non-nil, do opportunistic STARTTLS upgrades even if Emacs doesn’t have built-in TLS support.

:warn-unless-encrypted boolean

If non-nil, warn the user if the final connection type is not encrypted. This is useful for protocols like IMAP and the like, where most users would expect the network traffic to be encrypted. This may be due to STARTTLS upgrade failure, specifying :return-list non-nil allows you to capture any error encountered.

:client-certificate list-or-t ¶

Either a list of the form (key-file cert-file), naming the certificate key file and certificate file itself, or t, meaning to query auth-source for this information (see auth-source in Emacs auth-source Library). Only used for TLS or STARTTLS. To enable automatic queries of auth-source when :client-certificate is not specified customize network-stream-use-client-certificates to t.

:return-list cons-or-nil

The return value of this function. If omitted or nil, return a process object. Otherwise, a cons of the form (process-object . plist), where plist can include the following keywords:

:greeting string-or-nil

If non-nil, the greeting string returned by the host.

:capabilities string-or-nil

If non-nil, the host’s capability string.

:type symbol

The connection type: ‘plain’ or ‘tls’.

:error symbol

A string describing any error encountered when performing STARTTLS upgrade.

:shell-command string-or-nil

If the connection type is shell, this parameter will be interpreted as a format-spec string (see Custom Format Strings) that will be executed to make the connection. The specs available are ‘%s’ for the host name and ‘%p’ for the port number. For instance, if you want to first ssh to ‘gateway’ before making a plain connection, then this parameter’s value could be something like ‘ssh gateway nc %s %p’.

Next: Datagrams, Previous: Network Connections, Up: Processes   [Contents][Index]

41.15 Network Servers ¶

You create a server by calling make-network-process (see make-network-process) with :server t. The server will listen for connection requests from clients. When it accepts a client connection request, that creates a new network connection, itself a process object, with the following parameters:

• The connection’s process name is constructed by concatenating the server process’s name with a client identification string. The client identification string for an IPv4 connection looks like ‘<a.b.c.d:p>’, which represents an address and port number. Otherwise, it is a unique number in brackets, as in ‘<nnn>’. The number is unique for each connection in the Emacs session.
• If the server has a non-default filter, the connection process does not get a separate process buffer; otherwise, Emacs creates a new buffer for the purpose. The buffer name is the server’s buffer name or process name, concatenated with the client identification string.

  The server’s process buffer value is never used directly, but the log function can retrieve it and use it to log connections by inserting text there.

• The communication type and the process filter and sentinel are inherited from those of the server. The server never directly uses its filter and sentinel; their sole purpose is to initialize connections made to the server.
• The connection’s process contact information is set according to the client’s addressing information (typically an IP address and a port number). This information is associated with the process-contact keywords :host, :service, :remote.
• The connection’s local address is set up according to the port number used for the connection.
• The client process’s plist is initialized from the server’s plist.

Next: Low-Level Network Access, Previous: Network Servers, Up: Processes   [Contents][Index]

41.16 Datagrams ¶

A datagram connection communicates with individual packets rather than streams of data. Each call to process-send sends one datagram packet (see Sending Input to Processes), and each datagram received results in one call to the filter function.

The datagram connection doesn’t have to talk with the same remote peer all the time. It has a remote peer address which specifies where to send datagrams to. Each time an incoming datagram is passed to the filter function, the peer address is set to the address that datagram came from; that way, if the filter function sends a datagram, it will go back to that place. You can specify the remote peer address when you create the datagram connection using the :remote keyword. You can change it later on by calling set-process-datagram-address.

Function: process-datagram-address process ¶

If process is a datagram connection or server, this function returns its remote peer address.

Function: set-process-datagram-address process address ¶

If process is a datagram connection or server, this function sets its remote peer address to address.

Next: Misc Network Facilities, Previous: Datagrams, Up: Processes   [Contents][Index]

41.17 Low-Level Network Access ¶

You can also create network connections by operating at a lower level than that of open-network-stream, using make-network-process.

• make-network-process
• Network Options
• Testing Availability of Network Features

(featurep 'make-network-process '(keyword value))

(featurep 'make-network-process 'keyword)

Next: Communicating with Serial Ports, Previous: Low-Level Network Access, Up: Processes   [Contents][Index]

41.18 Misc Network Facilities ¶

These additional functions are useful for creating and operating on network connections. Note that they are supported only on some systems.

Function: network-interface-list &optional full family ¶

This function returns a list describing the network interfaces of the machine you are using. The value is an alist whose elements have the form (ifname . address). ifname is a string naming the interface, address has the same form as the local-address and remote-address arguments to make-network-process, i.e. a vector of integers. By default both IPv4 and IPv6 addresses are returned if possible.

Optional argument full non-nil means to instead return a list of one or more elements of the form (ifname addr bcast netmask). ifname is a non-unique string naming the interface. addr, bcast, and netmask are vectors of integers detailing the IP address, broadcast address, and network mask.

Optional argument family specified as symbol ipv4 or ipv6 restricts the returned information to IPv4 and IPv6 addresses respectively, independently of the value of full. Specifying ipv6 when IPv6 support is not available will result in an error being signaled.

Some examples:

(network-interface-list) ⇒
(("vmnet8" .
  [172 16 76 1 0])
 ("vmnet1" .
  [172 16 206 1 0])
 ("lo0" .
  [65152 0 0 0 0 0 0 1 0])
 ("lo0" .
  [0 0 0 0 0 0 0 1 0])
 ("lo0" .
  [127 0 0 1 0]))

(network-interface-list t) ⇒
(("vmnet8"
  [172 16 76 1 0]
  [172 16 76 255 0]
  [255 255 255 0 0])
 ("vmnet1"
  [172 16 206 1 0]
  [172 16 206 255 0]
  [255 255 255 0 0])
 ("lo0"
  [65152 0 0 0 0 0 0 1 0]
  [65152 0 0 0 65535 65535 65535 65535 0]
  [65535 65535 65535 65535 0 0 0 0 0])
 ("lo0"
  [0 0 0 0 0 0 0 1 0]
  [0 0 0 0 0 0 0 1 0]
  [65535 65535 65535 65535 65535 65535 65535 65535 0])
 ("lo0"
  [127 0 0 1 0]
  [127 255 255 255 0]
  [255 0 0 0 0]))

Function: network-interface-info ifname ¶

This function returns information about the network interface named ifname. The value is a list of the form (addr bcast netmask hwaddr flags).

addr

The Internet protocol address.

bcast

The broadcast address.

netmask

The network mask.

hwaddr

The layer 2 address (Ethernet MAC address, for instance).

flags

The current flags of the interface.

Note that this function returns only IPv4 information.

Function: format-network-address address &optional omit-port ¶

This function converts the Lisp representation of a network address to a string.

A five-element vector [a b c d p] represents an IPv4 address a.b.c.d and port number p. format-network-address converts that to the string "a.b.c.d:p".

A nine-element vector [a b c d e f g h p] represents an IPv6 address along with a port number. format-network-address converts that to the string "[a:b:c:d:e:f:g:h]:p".

If the vector does not include the port number, p, or if omit-port is non-nil, the result does not include the :p suffix.

Function: network-lookup-address-info name &optional family hints ¶

This function perform hostname lookups on name, which is expected to be an ASCII-only string, otherwise it signals an error. Call puny-encode-domain on name first if you wish to lookup internationalized hostnames.

If successful, this function returns a list of Lisp representations of network addresses (see make-network-process, for a description of the format), otherwise return nil. In the latter case, it also logs an error message hopefully explaining what went wrong.

By default, this function attempts both IPv4 and IPv6 lookups. The optional argument family controls this behavior, specifying the symbol ipv4 or ipv6 restricts lookups to IPv4 and IPv6 respectively.

If optional argument hints is numeric, the function treats the name as a numerical IP address (and does not perform DNS lookups). This can be used to check whether a string is a valid numerical representation of an IP address, or to convert a numerical string to its canonical representation. e.g.

(network-lookup-address-info "127.1" 'ipv4 'numeric)
    ⇒ ([127 0 0 1 0])

(network-lookup-address-info "::1" nil 'numeric)
    ⇒ ([0 0 0 0 0 0 0 1 0])

Be warned that there are some surprising valid forms, especially for IPv4, e.g ‘0xe3010203’ and ‘0343.1.2.3’ are both valid, as are ‘0’ and ‘1’ (but they are invalid for IPv6).

Next: Packing and Unpacking Byte Arrays, Previous: Misc Network Facilities, Up: Processes   [Contents][Index]

41.19 Communicating with Serial Ports ¶

Emacs can communicate with serial ports. For interactive use, M-x serial-term opens a terminal window. In a Lisp program, make-serial-process creates a process object.

The serial port can be configured at run-time, without having to close and re-open it. The function serial-process-configure lets you change the speed, bytesize, and other parameters. In a terminal window created by serial-term, you can click on the mode line for configuration.

A serial connection is represented by a process object, which can be used in a similar way to a subprocess or network process. You can send and receive data, and configure the serial port. A serial process object has no process ID, however, and you can’t send signals to it, and the status codes are different from other types of processes. delete-process on the process object or kill-buffer on the process buffer close the connection, but this does not affect the device connected to the serial port.

The function process-type returns the symbol serial for a process object representing a serial port connection.

Serial ports are available on GNU/Linux, Unix, and MS Windows systems.

Command: serial-term port speed &optional line-mode ¶

Start a terminal-emulator for a serial port in a new buffer. port is the name of the serial port to connect to. For example, this could be /dev/ttyS0 on Unix. On MS Windows, this could be COM1, or \\.\COM10 (double the backslashes in Lisp strings).

speed is the speed of the serial port in bits per second. 9600 is a common value. The buffer is in Term mode; see Term Mode in The GNU Emacs Manual, for the commands to use in that buffer. You can change the speed and the configuration in the mode line menu. If line-mode is non-nil, term-line-mode is used; otherwise term-raw-mode is used.

Function: make-serial-process &rest args ¶

This function creates a process and a buffer. Arguments are specified as keyword/argument pairs. Here’s the list of the meaningful keywords, with the first two (port and speed) being mandatory:

:port port

This is the name of the serial port. On Unix and GNU systems, this is a file name such as /dev/ttyS0. On Windows, this could be COM1, or \\.\COM10 for ports higher than COM9 (double the backslashes in Lisp strings).

:speed speed

The speed of the serial port in bits per second. This function calls serial-process-configure to handle the speed; see the following documentation of that function for more details.

:name name

The name of the process. If name is not given, port will serve as the process name as well.

:buffer buffer

The buffer to associate with the process. The value can be either a buffer or a string that names a buffer. Process output goes at the end of that buffer, unless you specify an output stream or filter function to handle the output. If buffer is not given, the process buffer’s name is taken from the value of the :name keyword.

:coding coding

If coding is a symbol, it specifies the coding system used for both reading and writing for this process. If coding is a cons (decoding . encoding), decoding is used for reading, and encoding is used for writing. If not specified, the default is to determine the coding systems from the data itself.

:noquery query-flag

Initialize the process query flag to query-flag. See Querying Before Exit. The flags defaults to nil if unspecified.

:stop bool

Start process in the stopped state if bool is non-nil. In the stopped state, a serial process does not accept incoming data, but you can send outgoing data. The stopped state is cleared by continue-process and set by stop-process.

:filter filter

Install filter as the process filter.

:sentinel sentinel

Install sentinel as the process sentinel.

:plist plist

Install plist as the initial plist of the process.

:bytesize

:parity

:stopbits

:flowcontrol

These are handled by serial-process-configure, which is called by make-serial-process.

The original argument list, possibly modified by later configuration, is available via the function process-contact.

Here is an example:

(make-serial-process :port "/dev/ttyS0" :speed 9600)

Function: serial-process-configure &rest args ¶

This function configures a serial port connection. Arguments are specified as keyword/argument pairs. Attributes that are not given are re-initialized from the process’s current configuration (available via the function process-contact), or set to reasonable default values. The following arguments are defined:

:process process

:name name

:buffer buffer

:port port

Any of these arguments can be given to identify the process that is to be configured. If none of these arguments is given, the current buffer’s process is used.

:speed speed

The speed of the serial port in bits per second, a.k.a. baud rate. The value can be any number, but most serial ports work only at a few defined values between 1200 and 115200, with 9600 being the most common value. If speed is nil, the function ignores all other arguments and does not configure the port. This may be useful for special serial ports such as Bluetooth-to-serial converters, which can only be configured through ‘AT’ commands sent through the connection. The value of nil for speed is valid only for connections that were already opened by a previous call to make-serial-process or serial-term.

:bytesize bytesize

The number of bits per byte, which can be 7 or 8. If bytesize is not given or nil, it defaults to 8.

:parity parity

The value can be nil (don’t use parity), the symbol odd (use odd parity), or the symbol even (use even parity). If parity is not given, it defaults to no parity.

:stopbits stopbits

The number of stopbits used to terminate a transmission of each byte. stopbits can be 1 or 2. If stopbits is not given or nil, it defaults to 1.

:flowcontrol flowcontrol

The type of flow control to use for this connection, which is either nil (don’t use flow control), the symbol hw (use RTS/CTS hardware flow control), or the symbol sw (use XON/XOFF software flow control). If flowcontrol is not given, it defaults to no flow control.

Internally, make-serial-process calls serial-process-configure for the initial configuration of the serial port.

Previous: Communicating with Serial Ports, Up: Processes   [Contents][Index]

41.20 Packing and Unpacking Byte Arrays ¶

This section describes how to pack and unpack arrays of bytes, usually for binary network protocols. These functions convert byte arrays to alists, and vice versa. The byte array can be represented as a unibyte string or as a vector of integers, while the alist associates symbols either with fixed-size objects or with recursive sub-alists. To use the functions referred to in this section, load the bindat library.

Conversion from byte arrays to nested alists is also known as deserializing or unpacking, while going in the opposite direction is also known as serializing or packing.

• Describing Data Layout
• Functions to Unpack and Pack Bytes
• Advanced data layout specifications

(bindat-type
  (len      u8)
  (payload  vec (1+ len) uint 16))

(bindat-type
  (len      u8)
  (payload  . (if (zerop len) (uint 24) (vec (1- len)))))

(defconst sint16-bindat-spec
  (let* ((max (ash 1 15))
         (wrap (+ max max)))
    (bindat-type :pack-var v
                 (n uint 16 :pack-val (if (< v 0) (+ v wrap) v))
                 :unpack-val (if (>= n max) (- n wrap) n))))

(bindat-pack sint16-bindat-spec -8)
     ⇒ "\377\370"

(bindat-unpack sint16-bindat-spec "\300\100")
     ⇒ -16320