This is Info file elisp, produced by Makeinfo-1.55 from the input file elisp.texi. This version is the edition 2.3 of the GNU Emacs Lisp Reference Manual. It corresponds to Emacs Version 19.23. Published by the Free Software Foundation 675 Massachusetts Avenue Cambridge, MA 02139 USA Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU General Public License" is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled "GNU General Public License" may be included in a translation approved by the Free Software Foundation instead of in the original English.  File: elisp, Node: Processes, Next: System Interface, Prev: Abbrevs, Up: Top Processes ********* In the terminology of operating systems, a "process" is a space in which a program can execute. Emacs runs in a process. Emacs Lisp programs can invoke other programs in processes of their own. These are called "subprocesses" or "child processes" of the Emacs process, which is their "parent process". A subprocess of Emacs may be "synchronous" or "asynchronous", depending on how it is created. When you create a synchronous subprocess, the Lisp program waits for the subprocess to terminate before continuing execution. When you create an asynchronous subprocess, it can run in parallel with the Lisp program. This kind of subprocess is represented within Emacs by a Lisp object which is also called a "process". Lisp programs can use this object to communicate with the subprocess or to control it. For example, you can send signals, obtain status information, receive output from the process, or send input to it. - Function: processp OBJECT This function returns `t' if OBJECT is a process, `nil' otherwise. * Menu: * Subprocess Creation:: Functions that start subprocesses. * 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. * Input to Processes:: Sending input to an asynchronous subprocess. * Signals to Processes:: Stopping, continuing or interrupting an asynchronous subprocess. * Output from Processes:: Collecting output from an asynchronous subprocess. * Sentinels:: Sentinels run when process run-status changes. * Transaction Queues:: Transaction-based communication with subprocesses. * TCP:: Opening network connections.  File: elisp, Node: Subprocess Creation, Next: Synchronous Processes, Up: Processes Functions that Create Subprocesses ================================== There are three functions that create a new subprocess in which to run a program. One of them, `start-process', creates an asynchronous process and returns a process object (*note Asynchronous Processes::.). The other two, `call-process' and `call-process-region', create a synchronous process and do not return a process object (*note Synchronous Processes::.). Synchronous and asynchronous processes are explained in following sections. Since the three functions are all called in a similar fashion, their common arguments are described here. In all cases, the function's PROGRAM argument specifies 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 (*note File Name Expansion::.). Each of the subprocess-creating functions has a BUFFER-OR-NAME argument which specifies where the standard output from the program will go. If BUFFER-OR-NAME is `nil', that says to discard the output unless a filter function handles it. (*Note Filter Functions::, and *Note Read and Print::.) Normally, you should avoid having multiple processes send output to the same buffer because their output would be intermixed randomly. All three of the subprocess-creating functions have a `&rest' argument, ARGS. The ARGS must all be strings, and they are supplied to PROGRAM as separate command line arguments. Wildcard characters and other shell constructs are not allowed in these strings, since they are passed directly to the specified program. *Please note:* the argument PROGRAM contains only the name of the program; it may not contain any command-line arguments. You must use ARGS to provide those. The subprocess gets its current directory from the value of `default-directory' (*note File Name Expansion::.). The subprocess inherits its environment from Emacs; but you can specify overrides for it with `process-environment'. *Note System Environment::. - Variable: exec-directory 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 to invoke. The program `wakeup' is an example of such a program; the `display-time' command uses it to get a reminder once per minute. - 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'). The value of `exec-path' is used by `call-process' and `start-process' when the PROGRAM argument is not an absolute file name.  File: elisp, Node: Synchronous Processes, Next: MS-DOS Subprocesses, Prev: Subprocess Creation, Up: Processes Creating a Synchronous Process ============================== After a "synchronous process" is created, Emacs waits for the process to terminate before continuing. Starting Dired 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. *Note Quitting::. The synchronous subprocess functions returned `nil' in version 18. In version 19, they return an indication of how the process terminated. - Function: call-process PROGRAM &optional INFILE BUFFER-OR-NAME DISPLAY &rest ARGS This function calls PROGRAM in a separate process and waits for it to finish. The standard input for the process comes from file INFILE if INFILE is not `nil' and from `/dev/null' otherwise. The process output gets inserted in buffer BUFFER-OR-NAME before point, if that argument names a buffer. If BUFFER-OR-NAME is `t', output is sent to the current buffer; if BUFFER-OR-NAME is `nil', output is discarded. If BUFFER-OR-NAME is the integer 0, `call-process' returns `nil' immediately and discards any output. 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. If DISPLAY is non-`nil', then `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 remaining arguments, ARGS, are strings that specify command line arguments for the program. 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. In the examples below, the buffer `foo' is current. (call-process "pwd" nil t) => nil ---------- Buffer: foo ---------- /usr/user/lewis/manual ---------- Buffer: foo ---------- (call-process "grep" nil "bar" nil "lewis" "/etc/passwd") => nil ---------- Buffer: bar ---------- lewis:5LTsHm66CSWKg:398:21:Bil Lewis:/user/lewis:/bin/csh ---------- Buffer: bar ---------- The `insert-directory' function contains a good example of the use of `call-process': (call-process insert-directory-program nil t nil switches (if full-directory-p (concat (file-name-as-directory file) ".") file)) - Function: call-process-region START END PROGRAM &optional DELETE BUFFER-OR-NAME DISPLAY &rest ARGS This function sends the text between 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 BUFFER is `t', to insert the output in the current buffer. The arguments BUFFER-OR-NAME 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 BUFFER-OR-NAME is the integer 0, `call-process-region' discards the output and returns `nil' immediately, without waiting for the subprocess to finish. 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 BUFFER-OR-NAME is `t', this output is inserted in the current buffer. ---------- Buffer: foo ---------- input-!- ---------- Buffer: foo ---------- (call-process-region 1 6 "cat" nil t) => nil ---------- Buffer: foo ---------- inputinput-!- ---------- Buffer: foo ---------- The `shell-command-on-region' command uses `call-process-region' like this: (call-process-region start end shell-file-name ; Name of program. nil ; Do not delete region. buffer ; Send output to `buffer'. nil ; No redisplay during output. "-c" command) ; Arguments for the shell.  File: elisp, Node: MS-DOS Subprocesses, Next: Asynchronous Processes, Prev: Synchronous Processes, Up: Processes 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, CRLF). The variable `binary-process-input' applies to input sent to the subprocess, and `binary-process-output' applies to output received from it. A non-`nil' value means the data is non-text; `nil' means the data is text, and calls for conversion. - Variable: binary-process-input If this variable is `nil', convert newlines to CRLF sequences in the input to a synchronous subprocess. - Variable: binary-process-output If this variable is `nil', convert CRLF sequences to newlines in the output from a synchronous subprocess. *Note Files and MS-DOS::, for related information.  File: elisp, Node: Asynchronous Processes, Next: Deleting Processes, Prev: MS-DOS Subprocesses, Up: Processes Creating an Asynchronous Process ================================ After an "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 `start-process'. - Function: start-process NAME BUFFER-OR-NAME PROGRAM &rest ARGS This function creates a new asynchronous subprocess and starts the program 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; if a process with this name already exists, then NAME is modified (by adding `<1>', etc.) to be unique. The buffer BUFFER-OR-NAME is the buffer to associate with the process. The remaining arguments, ARGS, are strings that specify command line arguments for the program. In the example below, the first process is started and runs (rather, sleeps) for 100 seconds. 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") => # (start-process "my-process" "foo" "ls" "-l" "/user/lewis/bin") => #> ---------- Buffer: foo ---------- total 2 lrwxrwxrwx 1 lewis 14 Jul 22 10:12 gnuemacs --> /emacs -rwxrwxrwx 1 lewis 19 Jul 30 21:02 lemon Process my-process<1> finished Process my-process finished ---------- Buffer: foo ---------- - Function: start-process-shell-command NAME BUFFER-OR-NAME COMMAND &rest COMMAND-ARGS This function is like `start-process' except that it uses a shell to execute the specified command. The argument COMMAND is a shell command name, and COMMAND-ARGS are the arguments for the shell command. - Variable: process-connection-type This variable controls the type of device used to communicate with asynchronous subprocesses. If it is `nil', then pipes are used. If it is `t', then PTYs are used (or pipes if PTYs are not supported). PTYs are usually preferable for processes visible to the user, as in Shell mode, because they allow job control (`C-c', `C-z', etc.) to work between the process and its children whereas pipes do not. For subprocesses used for internal purposes by programs, it is often better to use a pipe, because they are more efficient. In addition, the total number of PTYs is limited on many systems and it is good not to waste them. The value `process-connection-type' is used when `start-process' is called. So you can specify how to communicate with one subprocess by binding the variable around the call to `start-process'. (let ((process-connection-type nil)) ; Use a pipe. (start-process ...))  File: elisp, Node: Deleting Processes, Next: Process Information, Prev: Asynchronous Processes, Up: Processes Deleting Processes ================== "Deleting a process" disconnects Emacs immediately from the subprocess, and removes it from the list of active processes. It sends a signal to the subprocess to make the subprocess terminate, but this is not guaranteed to happen immediately. The process object itself continues to exist as long as other Lisp objects point to it. You can delete a process explicitly at any time. Processes are deleted automatically after they terminate, but not necessarily right away. If you delete a terminated process explicitly before it is deleted automatically, no harm results. - Variable: 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 NAME This function deletes the process associated with NAME, killing it with a `SIGHUP' signal. The argument NAME may be a process, the name of a process, a buffer, or the name of a buffer. (delete-process "*shell*") => nil - Function: process-kill-without-query PROCESS This function declares that Emacs need not query the user if PROCESS is still running when Emacs is exited. The process will be deleted silently. The value is `t'. (process-kill-without-query (get-process "shell")) => t  File: elisp, Node: Process Information, Next: Input to Processes, Prev: Deleting Processes, Up: Processes Process Information =================== Several functions return information about processes. `list-processes' is provided for interactive use. - Command: list-processes 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'. - Function: process-list This function returns a list of all processes that have not been deleted. (process-list) => (# #) - Function: get-process NAME This function returns the process named NAME, or `nil' if there is none. An error is signaled if NAME is not a string. (get-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. (process-command (get-process "shell")) => ("/bin/csh" "-i") - Function: process-id PROCESS This function returns the PID of PROCESS. This is an integer which 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. - Function: process-name PROCESS This function returns the name of PROCESS. - 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, a process name (string) or a buffer name (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 connection that is open. `closed' for a network 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. `nil' if PROCESS-NAME is not the name of an existing process. (process-status "shell") => run (process-status (get-buffer "*shell*")) => run x => #> (process-status x) => exit For a network connection, `process-status' returns one of the symbols `open' or `closed'. The latter means that the other side closed the connection, or Emacs did `delete-process'. In earlier Emacs versions (prior to version 19), the status of a network connection was `run' if open, and `exit' if closed. - 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.  File: elisp, Node: Input to Processes, Next: Signals to Processes, Prev: Process Information, Up: Processes 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. The data appears on the "standard input" of the subprocess. 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. - Function: process-send-string PROCESS-NAME STRING This function sends PROCESS-NAME the contents of STRING as standard input. The argument PROCESS-NAME must be a process or the name of a process. If it is `nil', the current buffer's process is used. The function returns `nil'. (process-send-string "shell<1>" "ls\n") => nil ---------- Buffer: *shell* ---------- ... introduction.texi syntax-tables.texi~ introduction.texi~ text.texi introduction.txt text.texi~ ... ---------- Buffer: *shell* ---------- - Command: process-send-region PROCESS-NAME START END This function sends the text in the region defined by START and END as standard input to PROCESS-NAME, which is a process or a process name. (If it is `nil', the current buffer's process is used.) 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-NAME This function makes PROCESS-NAME see an end-of-file in its input. The EOF comes after any text already sent to it. If PROCESS-NAME is not supplied, or if it is `nil', then this function sends the EOF to the current buffer's process. An error is signaled if the current buffer has no process. The function returns PROCESS-NAME. (process-send-eof "shell") => "shell"  File: elisp, Node: Signals to Processes, Next: Output from Processes, Prev: Input to Processes, Up: Processes 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.) Each of the signal-sending functions takes two optional arguments: PROCESS-NAME and CURRENT-GROUP. The argument PROCESS-NAME must be either a process, the name of one, or `nil'. If it is `nil', the process defaults to the process associated with the current buffer. An error is signaled if PROCESS-NAME does not identify a process. 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 which Emacs uses to communicate with the subprocess. If the process is a job-control shell, this means the shell's current subjob. If it 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. 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 *Note Asynchronous Processes::. - Function: interrupt-process &optional PROCESS-NAME CURRENT-GROUP This function interrupts the process PROCESS-NAME 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. - Function: kill-process &optional PROCESS-NAME CURRENT-GROUP This function kills the process PROCESS-NAME by sending the signal `SIGKILL'. This signal kills the subprocess immediately, and cannot be handled by the subprocess. - Function: quit-process &optional PROCESS-NAME CURRENT-GROUP This function sends the signal `SIGQUIT' to the process PROCESS-NAME. This signal is the one sent by the "quit character" (usually `C-b' or `C-\') when you are not inside Emacs. - Function: stop-process &optional PROCESS-NAME CURRENT-GROUP This function stops the process PROCESS-NAME by sending the signal `SIGTSTP'. Use `continue-process' to resume its execution. On systems with job control, the "stop character" (usually `C-z') sends this signal (outside of Emacs). 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-NAME CURRENT-GROUP This function resumes execution of the process PROCESS by sending it the signal `SIGCONT'. This presumes that PROCESS-NAME was stopped previously. - Function: signal-process PID SIGNAL This function sends a signal to process PID, which need not be a child of Emacs. The argument SIGNAL specifies which signal to send; it should be an integer.  File: elisp, Node: Output from Processes, Next: Sentinels, Prev: Signals to Processes, Up: Processes Receiving Output from Processes =============================== There are two ways to receive the output that a subprocess writes to its standard output stream. The output can be inserted in a buffer, which is called the associated buffer of the process, or a function called the "filter function" can be called to act on the output. * Menu: * Process Buffers:: If no filter, output is put in a buffer. * Filter Functions:: Filter functions accept output from the process. * Accepting Output:: Explicitly permitting subprocess output. Waiting for subprocess output.  File: elisp, Node: Process Buffers, Next: Filter Functions, Up: Output from Processes Process Buffers --------------- A process can (and usually does) have an "associated buffer", which is an ordinary Emacs buffer that is used for two purposes: storing the output from the process, and deciding when to kill the process. You can also use the buffer to identify a process to operate on, since in normal practice only one process is associated with any given buffer. Many applications of processes also use the buffer for editing input to be sent to the process, but this is not built into Emacs Lisp. Unless the process has a filter function (*note Filter Functions::.), its output is inserted in the associated buffer. The position to insert the output is determined by the `process-mark' (*note Process Information::.), which is then updated to point to the end of the text just inserted. Usually, but not always, the `process-mark' is at the end of the buffer. If the process has no buffer and no filter function, its output is discarded. - Function: process-buffer PROCESS This function returns the associated buffer of the process PROCESS. (process-buffer (get-process "shell")) => # - Function: process-mark PROCESS This function returns the process marker for PROCESS, which is the marker that says where to insert output from the process. If PROCESS does not have a buffer, `process-mark' returns a marker that points nowhere. Insertion of process output in a buffer uses this marker to decide where to insert, and updates it to point after the inserted text. That is why successive batches of output are inserted consecutively. Filter functions normally should use this marker in the same fashion as is done by direct insertion of output in the buffer. A good example of a filter function that uses `process-mark' is found at the end of the following section. When the user is expected to enter input in the process buffer for transmission to the process, the process marker is useful for distinguishing the new input from previous output. - Function: set-process-buffer PROCESS BUFFER This function sets the buffer associated with PROCESS to BUFFER. If BUFFER is `nil', the process becomes associated with no buffer. - Function: get-buffer-process BUFFER-OR-NAME This function returns the process associated with BUFFER-OR-NAME. If there are several processes associated with it, then one is chosen. (Presently, the one chosen is the one most recently created.) It is usually a bad idea to have more than one process associated with the same buffer. (get-buffer-process "*shell*") => # Killing the process's buffer deletes the process, which kills the subprocess with a `SIGHUP' signal (*note Signals to Processes::.).  File: elisp, Node: Filter Functions, Next: Accepting Output, Prev: Process Buffers, Up: Output from Processes Process Filter Functions ------------------------ A process "filter function" is a function that receives the standard output from the associated process. If a process has a filter, then *all* output from that process, that would otherwise have been in a buffer, is passed to the filter. The process buffer is used directly for output from the process only when there is no filter. A filter function must accept two arguments: the associated process and a string, which is the output. 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 `sit-for', `sleep-for' or `accept-process-output' (*note 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 `C-g' at command level or to quit a user command would be unpredictable. If you want to permit quitting inside a filter function, bind `inhibit-quit' to `nil'. *Note Quitting::. Many filter functions sometimes or always insert the text in the process's buffer, mimicking the actions of Emacs when there is no filter. Such filter functions need to use `set-buffer' in order to be sure to insert in that buffer. To avoid setting the current buffer semipermanently, these filter functions must use `unwind-protect' to make sure to restore the previous current buffer. They should also update the process marker, and in some cases update the value of point. Here is how to do these things: (defun ordinary-insertion-filter (proc string) (let ((old-buffer (current-buffer))) (unwind-protect (let (moving) (set-buffer (process-buffer proc)) (setq moving (= (point) (process-mark proc))) (save-excursion ;; Insert the text, moving the process-marker. (goto-char (process-mark proc)) (insert string) (set-marker (process-mark proc) (point))) (if moving (goto-char (process-mark proc)))) (set-buffer old-buffer)))) The reason to use an explicit `unwind-protect' rather than letting `save-excursion' restore the current buffer is so as to preserve the change in point made by `goto-char'. To make the filter force the process buffer to be visible whenever new text arrives, insert the following line just before the `unwind-protect': (display-buffer (process-buffer proc)) To force point to move to the end of the new output no matter where it was previously, eliminate the variable `moving' and call `goto-char' unconditionally. All filter functions that do regexp searching or matching should save and restore the match data. Otherwise, a filter function that runs during a call to `sit-for' might clobber the match data of the program that called `sit-for'. *Note Match Data::. A filter function that writes the output into the buffer of the process should check whether the process 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'. The output to the function may come in chunks of any size. A program that produces the same output twice in a row may send it as one batch of 200 characters one time, and five batches of 40 characters the next. - Function: set-process-filter PROCESS FILTER This function gives PROCESS the filter function FILTER. If FILTER is `nil', it gives the process no filter. - Function: process-filter PROCESS This function returns the filter function of PROCESS, or `nil' if it has none. Here is an example of use of a filter function: (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[8] % " "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 ")  File: elisp, Node: Accepting Output, Prev: Filter Functions, Up: Output from Processes Accepting Output from Processes ------------------------------- Output from asynchronous subprocesses normally arrives only while Emacs is waiting for some sort of external event, such as elapsed time or terminal input. Occasionally it is useful in a Lisp program to explicitly permit output to arrive at a specific point, or even to wait until output arrives from a process. - Function: accept-process-output &optional PROCESS SECONDS MILLISEC This function allows Emacs to read pending output from processes. The output is inserted in the associated buffers or given to their filter functions. If PROCESS is non-`nil' then this function does not return until some output has been received from PROCESS. The arguments SECONDS and MILLISEC let you specify timeout periods. The former specifies a period measured in seconds and the latter specifies one measured in milliseconds. The two time periods thus specified are added together, and `accept-process-output' returns after that much time whether or not there has been any subprocess output. 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 nonzero MILLISEC. The function `accept-process-output' returns non-`nil' if it did get some output, or `nil' if the timeout expired before output arrived.  File: elisp, Node: Sentinels, Next: Transaction Queues, Prev: Output from Processes, Up: Processes 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. The string describing the event looks like one of the following: * `"finished\n"'. * `"exited abnormally with code EXITCODE\n"'. * `"NAME-OF-SIGNAL\n"'. * `"NAME-OF-SIGNAL (core dumped)\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 them at random places in the middle of other Lisp programs. A program can wait, so that sentinels will run, by calling `sit-for', `sleep-for' or `accept-process-output' (*note Accepting Output::.). Emacs is also waiting when the command loop is reading input. 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'. *Note Quitting::. A sentinel that writes the output into the buffer of the process should check whether the process 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'. All sentinels that do regexp searching or matching should save and restore the match data. Otherwise, a sentinel that runs during a call to `sit-for' might clobber the match data of the program that called `sit-for'. *Note Match Data::. - Function: set-process-sentinel PROCESS SENTINEL This function associates SENTINEL with PROCESS. If SENTINEL is `nil', then the process will have no sentinel. The default behavior when there is no sentinel is to insert a message in the process's buffer when the process status changes. (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: # had the event `killed' => # - Function: process-sentinel PROCESS This function returns the sentinel of PROCESS, or `nil' if it has none. - 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, `nil' if it was not.  File: elisp, Node: Transaction Queues, Next: TCP, Prev: Sentinels, Up: Processes Transaction Queues ================== You can use a "transaction queue" for more convenient communication with subprocesses 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 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 which 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 the entire answer, but nothing less; that's how `tq-enqueue' determines where the answer ends. The return value of `tq-enqueue' itself is not meaningful. - 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. *Note Filter Functions::.  File: elisp, Node: TCP, Prev: Transaction Queues, Up: Processes TCP === Emacs Lisp programs can open TCP connections 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, so 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 process at the other end; that process must decide what to do about closure of the connection. You can distinguish process objects representing network connections from those representing subprocesses with the `process-status' function. *Note Process Information::. - Function: open-network-stream NAME BUFFER-OR-NAME HOST SERVICE This function opens a TCP connection for a service to a host. It returns a process object to represent the connection. The NAME argument specifies the name for the process object. It is modified as necessary to make it unique. The BUFFER-OR-NAME argument is the buffer to associate with the connection. Output from the connection is inserted in the buffer, unless you specify a filter function to handle the output. If BUFFER-OR-NAME 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).  File: elisp, Node: System Interface, Next: Display, Prev: Processes, Up: Top Operating System Interface ************************** This chapter is about starting and getting out of Emacs, access to values in the operating system environment, and terminal input, output and flow control. *Note Building Emacs::, for related information. See also *Note Display::, for additional operating system status information pertaining to the terminal and the screen. * Menu: * Starting Up:: Customizing Emacs start-up processing. * Getting Out:: How exiting works (permanent or temporary). * System Environment:: Distinguish the name and kind of system. * User Identification:: Finding the name and user id of the user. * Time of Day:: Getting the current time. * Timers:: Setting a timer to call a function at a certain time. * Terminal Input:: Recording terminal input for debugging. * Terminal Output:: Recording terminal output for debugging. * Special Keysyms:: Defining system-specific key symbols for X windows. * Flow Control:: How to turn output flow control on or off. * Batch Mode:: Running Emacs without terminal interaction.  File: elisp, Node: Starting Up, Next: Getting Out, Up: System Interface Starting Up Emacs ================= This section describes what Emacs does when it is started, and how you can customize these actions. * Menu: * Start-up Summary:: Sequence of actions Emacs performs at start-up. * Init File:: Details on reading the init file (`.emacs'). * Terminal-Specific:: How the terminal-specific Lisp file is read. * Command Line Arguments:: How command line arguments are processed, and how you can customize them.  File: elisp, Node: Start-up Summary, Next: Init File, Up: Starting Up Summary: Sequence of Actions at Start Up ---------------------------------------- The order of operations performed (in `startup.el') by Emacs when it is started up is as follows: 1. It loads the initialization library for the window system, if you are using a window system. This library's name is `term/WINDOWSYSTEM-win.el'. 2. It initializes the X window frame and faces, if appropriate. 3. It runs the normal hook `before-init-hook'. 4. It loads the library `site-start', unless the option `-no-site-file' was specified. The library's file name is usually `site-start.el'. 5. It loads the file `~/.emacs' unless `-q' was specified on command line. (This is not done in `-batch' mode.) The `-u' option can specify the user name whose home directory should be used instead of `~'. 6. It loads the library `default' unless `inhibit-default-init' is non-`nil'. (This is not done in `-batch' mode or if `-q' was specified on command line.) The library's file name is usually `default.el'. 7. It runs the normal hook `after-init-hook'. 8. It sets the major mode according to `initial-major-mode', provided the buffer `*scratch*' is still current and still in Fundamental mode. 9. It loads the terminal-specific Lisp file, if any, except when in batch mode or using a window system. 10. It displays the initial echo area message, unless you have suppressed that with `inhibit-startup-echo-area-message'. 11. It processes any remaining command line arguments. 12. It runs `term-setup-hook'. 13. It calls `frame-notice-user-settings', which modifies the parameters of the selected frame according to whatever the init files specify. 14. It runs `window-setup-hook'. *Note Window Systems::. 15. It displays copyleft, nonwarranty and basic use information, provided there were no remaining command line arguments (a few steps above) and the value of `inhibit-startup-message' is `nil'. - User Option: inhibit-startup-message This variable inhibits the initial startup messages (the nonwarranty, etc.). If it is non-`nil', then the messages are not printed. This variable exists so you can set it in your personal init file, once you are familiar with the contents of the startup message. Do not set this variable in the init file of a new user, or in a way that affects more than one user, because that would prevent new users from receiving the information they are supposed to see. - User Option: inhibit-startup-echo-area-message This variable controls the display of the startup echo area message. You can suppress the startup echo area message by adding text with this form to your `.emacs' file: (setq inhibit-startup-echo-area-message "YOUR-LOGIN-NAME") Simply setting `inhibit-startup-echo-area-message' to your login name is not sufficient to inhibit the message; Emacs explicitly checks whether `.emacs' contains an expression as shown above. Your login name must appear in the expression as a Lisp string constant. This way, you can easily inhibit the message for yourself if you wish, but thoughtless copying of your `.emacs' file will not inhibit the message for someone else.