@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998 Free Software Foundation, Inc.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999
+@c Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/processes
-@node Processes, System Interface, Abbrevs, Top
+@node Processes, Display, Abbrevs, Top
@chapter Processes
@cindex child process
@cindex parent process
@menu
* Subprocess Creation:: Functions that start subprocesses.
+* Shell Arguments:: Quoting an argument to pass it to a shell.
* Synchronous Processes:: Details of using synchronous subprocesses.
-* MS-DOS Subprocesses:: On MS-DOS, you must indicate text vs binary
- for data sent to and from a subprocess.
* Asynchronous Processes:: Starting up an asynchronous subprocess.
* Deleting Processes:: Eliminating an asynchronous subprocess.
* Process Information:: Accessing run-status and other attributes.
create a synchronous process and do not return a process object
(@pxref{Synchronous Processes}).
- Synchronous and asynchronous processes are explained in following
+ 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.
Each of the subprocess-creating functions has a @var{buffer-or-name}
argument which specifies where the standard output from the program will
-go. It should be a buffer or a buffer name (which will create the
-buffer if it does not already exist). It can also be @code{nil}, which
-says to discard the output unless a filter function handles it.
-(@xref{Filter Functions}, and @ref{Read and Print}.) Normally, you
-should avoid having multiple processes send output to the same buffer
-because their output would be intermixed randomly.
+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 @code{nil}, which says to discard the output unless a filter function
+handles it. (@xref{Filter Functions}, and @ref{Read and Print}.)
+Normally, you should avoid having multiple processes send output to the
+same buffer because their output would be intermixed randomly.
@cindex program arguments
All three of the subprocess-creating functions have a @code{&rest}
@code{default-directory} (@pxref{File Name Expansion}).
@cindex environment variables, subprocesses
- The subprocess inherits its environment from Emacs; but you can
+ The subprocess inherits its environment from Emacs, but you can
specify overrides for it with @code{process-environment}. @xref{System
Environment}.
@defvar exec-directory
@pindex movemail
-The value of this variable is the name of a directory (a string) that
-contains programs that come with GNU Emacs, that are intended for Emacs
+The value of this variable is a string, the name of a directory that
+contains programs that come with GNU Emacs, programs intended for Emacs
to invoke. The program @code{movemail} is an example of such a program;
Rmail uses it to fetch new mail from an inbox.
@end defvar
file name.
@end defopt
+@node Shell Arguments
+@section 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 @code{shell-quote-argument}:
+
+@defun shell-quote-argument argument
+This function returns a string which represents, in shell syntax,
+an argument whose actual contents are @var{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.
+
+@example
+;; @r{This example shows the behavior on GNU and Unix systems.}
+(shell-quote-argument "foo > bar")
+ @result{} "foo\\ \\>\\ bar"
+
+;; @r{This example shows the behavior on MS-DOS and MS-Windows systems.}
+(shell-quote-argument "foo > bar")
+ @result{} "\"foo > bar\""
+@end example
+
+Here's an example of using @code{shell-quote-argument} to construct
+a shell command:
+
+@example
+(concat "diff -c "
+ (shell-quote-argument oldfile)
+ " "
+ (shell-quote-argument newfile))
+@end example
+@end defun
+
@node Synchronous Processes
@section Creating a Synchronous Process
@cindex synchronous subprocess
After a @dfn{synchronous process} is created, Emacs waits for the
-process to terminate before continuing. Starting Dired is an example of
-this: it runs @code{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.
+process to terminate before continuing. Starting Dired on GNU or
+Unix@footnote{On other systems, Emacs uses a Lisp emulation of
+@code{ls}; see @ref{Contents of Directories}.} is an example of this: it
+runs @code{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 @kbd{C-g}. The first @kbd{C-g} tries to kill
the subprocess with a @code{SIGINT} signal; but it waits until the
subprocess actually terminates before quitting. If during that time the
user types another @kbd{C-g}, that kills the subprocess instantly with
-@code{SIGKILL} and quits immediately. @xref{Quitting}.
+@code{SIGKILL} and quits immediately (except on MS-DOS, where killing
+other processes doesn't work). @xref{Quitting}.
- The synchronous subprocess functions returned @code{nil} in version
-18. Now they return an indication of how the process terminated.
+ 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
it to finish.
The standard input for the process comes from file @var{infile} if
-@var{infile} is not @code{nil}, and from @file{/dev/null} otherwise.
+@var{infile} is not @code{nil}, and from the null device otherwise.
The argument @var{destination} says where to put the process output.
Here are the possibilities:
standard output stream and the standard error stream of the process.
@item a string
-Find the buffer with that name, then insert the output in that buffer,
-before point.
+Insert the output in a buffer with that name, before point.
@item @code{t}
Insert the output in the current buffer, before point.
Discard the output.
@item 0
-Discard the output, and return immediately without waiting
+Discard the output, and return @code{nil} immediately without waiting
for the subprocess to finish.
In this case, the process is not truly synchronous, since it can run in
Emacs is essentially finished with the subprocess as soon as this
function returns.
-@item (@var{real-destination} @var{error-destination})
+MS-DOS doesn't support asynchronous subprocesses, so this option doesn't
+work there.
+
+@item @code{(@var{real-destination} @var{error-destination})}
Keep the standard output stream separate from the standard error stream;
deal with the ordinary output as specified by @var{real-destination},
and dispose of the error output according to @var{error-destination}.
-The value @code{nil} means discard it, @code{t} means mix it with the
-ordinary output, and a string specifies a file name to redirect error
-output into.
+If @var{error-destination} is @code{nil}, that means to discard the
+error output, @code{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
@end table
If @var{display} is non-@code{nil}, then @code{call-process} redisplays
-the buffer as output is inserted. Otherwise the function does no
-redisplay, and the results become visible on the screen only when Emacs
-redisplays that buffer in the normal course of events.
+the buffer as output is inserted. (However, if the coding system chosen
+for decoding output is @code{undecided}, meaning deduce the encoding
+from the actual data, then redisplay sometimes cannot continue once
+non-@sc{ascii} characters are encountered. There are fundamental
+reasons why it is hard to fix this; see @ref{Output from Processes}.)
+
+Otherwise the function @code{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, @var{args}, are strings that specify command
line arguments for the program.
@smallexample
@group
(call-process "pwd" nil t)
- @result{} nil
+ @result{} 0
---------- Buffer: foo ----------
/usr/user/lewis/manual
@group
(call-process "grep" nil "bar" nil "lewis" "/etc/passwd")
- @result{} nil
+ @result{} 0
---------- Buffer: bar ----------
lewis:5LTsHm66CSWKg:398:21:Bil Lewis:/user/lewis:/bin/csh
@end group
@end smallexample
-The @code{insert-directory} function contains a good example of the use
-of @code{call-process}:
+Here is a good example of the use of @code{call-process}, which used to
+be found in the definition of @code{insert-directory}:
@smallexample
@group
-(call-process insert-directory-program nil t nil switches
+(call-process insert-directory-program nil t nil @var{switches}
(if full-directory-p
(concat (file-name-as-directory file) ".")
file))
@end defun
@defun call-process-region start end program &optional delete destination display &rest args
-This function sends the text between @var{start} to @var{end} as
+This function sends the text from @var{start} to @var{end} as
standard input to a process running @var{program}. It deletes the text
sent if @var{delete} is non-@code{nil}; this is useful when
@var{destination} is @code{t}, to insert the output in the current
as it comes in. For details, see the description of
@code{call-process}, above. If @var{destination} is the integer 0,
@code{call-process-region} discards the output and returns @code{nil}
-immediately, without waiting for the subprocess to finish.
+immediately, without waiting for the subprocess to finish (this only
+works if asynchronous subprocesses are supported).
The remaining arguments, @var{args}, are strings that specify command
line arguments for the program.
@group
(call-process-region 1 6 "cat" nil t)
- @result{} nil
+ @result{} 0
---------- Buffer: foo ----------
inputinput@point{}
@end smallexample
@end defun
-@tindex shell-command-to-string
@defun shell-command-to-string command
This function executes @var{command} (a string) as a shell command,
then returns the command's output as a string.
@end defun
-@node MS-DOS Subprocesses
-@section MS-DOS Subprocesses
-
- On MS-DOS, you must indicate whether the data going to and from
-a synchronous subprocess are text or binary. Text data requires
-translation between the end-of-line convention used within Emacs
-(a single newline character) and the convention used outside Emacs
-(the two-character sequence, @sc{crlf}).
-
- The variable @code{binary-process-input} applies to input sent to the
-subprocess, and @code{binary-process-output} applies to output received
-from it. A non-@code{nil} value means the data is non-text; @code{nil}
-means the data is text, and calls for conversion.
-
-@defvar binary-process-input
-If this variable is @code{nil}, convert newlines to @sc{crlf} sequences in
-the input to a synchronous subprocess.
-@end defvar
-
-@defvar binary-process-output
-If this variable is @code{nil}, convert @sc{crlf} sequences to newlines in
-the output from a synchronous subprocess.
-@end defvar
-
- @xref{Files and MS-DOS}, for related information.
-
@node Asynchronous Processes
@section Creating an Asynchronous Process
@cindex asynchronous subprocess
- After an @dfn{asynchronous process} is created, Emacs and the Lisp
-program both continue running immediately. The process may thereafter
-run in parallel with Emacs, and the two may communicate with each other
-using the functions described in following sections. Here we describe
-how to create an asynchronous process with @code{start-process}.
+ After an @dfn{asynchronous process} is created, Emacs and the subprocess
+both continue running immediately. The process thereafter runs
+in parallel with Emacs, and the two can communicate with each other
+using the functions described in the following sections. However,
+communication is only partially asynchronous: Emacs sends data to the
+process only when certain functions are called, and Emacs accepts data
+from the process only when Emacs is waiting for input or for a time
+delay.
+
+ Here we describe how to create an asynchronous process.
@defun start-process name buffer-or-name program &rest args
This function creates a new asynchronous subprocess and starts the
command name, and @var{command-args} are the arguments for the shell
command. The variable @code{shell-file-name} specifies which shell to
use.
+
+The point of running a program through the shell, rather than directly
+with @code{start-process}, is so that you can employ shell features such
+as wildcards in the arguments. It follows that if you include an
+arbitrary user-specified arguments in the command, you should quote it
+with @code{shell-quote-argument} first, so that any special shell
+characters do @emph{not} have their special shell meanings. @xref{Shell
+Arguments}.
@end defun
@defvar process-connection-type
addition, the total number of @sc{pty}s is limited on many systems and
it is good not to waste them.
-The value @code{process-connection-type} is used when
+The value of @code{process-connection-type} is used when
@code{start-process} is called. So you can specify how to communicate
with one subprocess by binding the variable around the call to
@code{start-process}.
away. If you delete a terminated process explicitly before it is
deleted automatically, no harm results.
-@defvar delete-exited-processes
+@defopt delete-exited-processes
This variable controls automatic deletion of processes that have
terminated (due to calling @code{exit} or to a signal). If it is
@code{nil}, then they continue to exist until the user runs
@code{list-processes}. Otherwise, they are deleted immediately after
they exit.
-@end defvar
+@end defopt
@defun delete-process name
This function deletes the process associated with @var{name}, killing it
@end smallexample
@end defun
-@defun process-kill-without-query process
-This function declares that Emacs need not query the user if
-@var{process} is still running when Emacs is exited. The process will
-be deleted silently. The value is @code{t}.
+@defun process-kill-without-query process &optional do-query
+This function specifies whether Emacs should query the user if
+@var{process} is still running when Emacs is exited. If @var{do-query}
+is @code{nil}, the process will be deleted silently.
+Otherwise, Emacs will query about killing it.
+
+The value is @code{t} if the process was formerly set up to require
+query, @code{nil} otherwise. A newly-created process always requires
+query.
@smallexample
@group
This function returns the name of @var{process}.
@end defun
-@tindex process-contact
@defun process-contact process
This function returns @code{t} for an ordinary child process, and
@code{(@var{hostname} @var{service})} for a net connection
For a network connection, @code{process-status} returns one of the symbols
@code{open} or @code{closed}. The latter means that the other side
closed the connection, or Emacs did @code{delete-process}.
-
-In Emacs version 18, the status of a network connection was @code{run}
-if open, and @code{exit} if closed.
@end defun
@defun process-exit-status process
@ref{Asynchronous Processes}).
@end defun
-@tindex process-coding-system
@defun process-coding-system process
This function returns a cons cell describing the coding systems in use
for decoding output from @var{process} and for encoding input to
@var{process} (@pxref{Coding Systems}). The value has this form:
@example
-(@var{coding-system-for-decoding}
- . @var{coding-system-for-encoding})
+(@var{coding-system-for-decoding} . @var{coding-system-for-encoding})
@end example
@end defun
-@tindex set-process-coding-system
@defun set-process-coding-system process decoding-system encoding-system
This function specifies the coding systems to use for subsequent output
from and input to @var{process}. It will use @var{decoding-system} to
these @sc{eof}s do no harm.
Subprocess input is normally encoded using a coding system before the
-subprocess receives it, much like text written into a file.
-@xref{Coding Systems}.
+subprocess receives it, much like text written into a file. You can use
+@code{set-process-coding-system} to specify which coding system to use
+(@pxref{Process Information}). Otherwise, the coding system comes from
+@code{coding-system-for-write}, if that is non-@code{nil}; or else from
+the defaulting mechanism (@pxref{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, sentinels
+and timers to run---so take account of that in writing your code.
@defun process-send-string process-name string
This function sends @var{process-name} the contents of @var{string} as
@end smallexample
@end defun
-@deffn Command process-send-region process-name start end
+@defun process-send-region process-name start end
This function sends the text in the region defined by @var{start} and
@var{end} as standard input to @var{process-name}, which is a process or
a process name. (If it is @code{nil}, the current buffer's process is
An error is signaled unless both @var{start} and @var{end} are
integers or markers that indicate positions in the current buffer. (It
is unimportant which number is larger.)
-@end deffn
+@end defun
@defun process-send-eof &optional process-name
This function makes @var{process-name} see an end-of-file in its
@end smallexample
@end defun
+@defun process-running-child-p process
+@tindex process-running-child-p process
+This function will tell you whether a subprocess has given control of
+its terminal to its own child process. The value is @code{t} if this is
+true, or if Emacs cannot tell; it is @code{nil} if Emacs can be certain
+that this is not so.
+@end defun
+
@node Signals to Processes
@section Sending Signals to Processes
@cindex process signals
signal @code{SIGTSTP}. Use @code{continue-process} to resume its
execution.
-On systems with job control, outside of Emacs)\, the ``stop character''
+Outside of Emacs, on systems with job control, the ``stop character''
(usually @kbd{C-z}) normally sends this signal. When
@var{current-group} is non-@code{nil}, you can think of this function as
``typing @kbd{C-z}'' on the terminal Emacs uses to communicate with the
called the @dfn{filter function} can be called to act on the output. If
the process has no buffer and no filter function, its output is
discarded.
+
+ Output from a subprocess can arrive only while Emacs is waiting: when
+reading terminal input, in @code{sit-for} and @code{sleep-for}
+(@pxref{Waiting}), and in @code{accept-process-output} (@pxref{Accepting
+Output}). 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.
+
+ It is impossible to separate the standard output and standard error
+streams of the subprocess, because Emacs normally spawns the subprocess
+inside a pseudo-TTY, and a pseudo-TTY has only one output channel. If
+you want to keep the output to those streams separate, you should
+redirect one of them to a file--for example, by using an appropriate
+shell command.
Subprocess output is normally decoded using a coding system before the
buffer or filter function receives it, much like text read from a file.
-@xref{Coding Systems}.
+You can use @code{set-process-coding-system} to specify which coding
+system to use (@pxref{Process Information}). Otherwise, the coding
+system comes from @code{coding-system-for-read}, if that is
+non-@code{nil}; or else from the defaulting mechanism (@pxref{Default
+Coding Systems}).
+
+ @strong{Warning:} Coding systems such as @code{undecided} which
+determine the coding system from the data do not work entirely reliably
+with asynchronous subprocess output. This is because Emacs has to
+process asynchronous subprocess output in batches, as it arrives. Emacs
+must try to detect the proper coding system from one batch at a time,
+and this does not always work. Therefore, if at all possible, use a
+coding system which determines both the character code conversion and
+the end of line conversion---that is, one like @code{latin-1-unix},
+rather than @code{undecided} or @code{latin-1}.
@menu
* Process Buffers:: If no filter, output is put in a buffer.
process buffer is used directly for output from the process only when
there is no filter.
+ The filter function can only be called when Emacs is waiting for
+something, because process output arrives only at such times. Emacs
+waits when reading terminal input, in @code{sit-for} and
+@code{sleep-for} (@pxref{Waiting}), and in @code{accept-process-output}
+(@pxref{Accepting Output}).
+
A filter function must accept two arguments: the associated process
and a string, which is output just received from it. The function is
then free to do whatever it chooses with the output.
- A filter function 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 filters at random places in
-the middle of other Lisp programs. You may explicitly cause Emacs to
-wait, so that filter functions will run, by calling @code{sit-for} or
-@code{sleep-for} (@pxref{Waiting}), or @code{accept-process-output}
-(@pxref{Accepting Output}). Emacs is also waiting when the command loop
-is reading input.
-
Quitting is normally inhibited within a filter function---otherwise,
the effect of typing @kbd{C-g} at command level or to quit a user
command would be unpredictable. If you want to permit quitting inside a
The argument @var{seconds} need not be an integer. If it is a floating
point number, this function waits for a fractional number of seconds.
Some systems support only a whole number of seconds; on these systems,
-@var{seconds} is rounded down. If the system doesn't support waiting
-fractions of a second, you get an error if you specify nonzero
-@var{millisec}.
+@var{seconds} is rounded down.
Not all operating systems support waiting periods other than multiples
of a second; on those that do not, you get an error if you specify
middle of other Lisp programs. A program can wait, so that sentinels
will run, by calling @code{sit-for} or @code{sleep-for}
(@pxref{Waiting}), or @code{accept-process-output} (@pxref{Accepting
-Output}). Emacs is also waiting when the command loop is reading input.
+Output}). Emacs also allows sentinels to run when the command loop is
+reading input.
Quitting is normally inhibited within a sentinel---otherwise, the
effect of typing @kbd{C-g} at command level or to quit a user command
HCoop / bpt / emacs.git / blobdiff