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This is Info file elisp, produced by Makeinfo-1.47 from the input file elisp.texi. This file documents GNU Emacs Lisp. This is edition 1.03 of the GNU Emacs Lisp Reference Manual, for Emacs Version 18. Published by the Free Software Foundation, 675 Massachusetts Avenue, Cambridge, MA 02139 USA Copyright (C) 1990 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. File: elisp, Node: Syntax Class Table, Next: Syntax Flags, Prev: Syntax Descriptors, Up: Syntax Descriptors Table of Syntax Classes ----------------------- Here is a summary of the classes, the characters that stand for them, their meanings, and examples of their use. -- Syntax class: whitespace character "Whitespace characters" (designated with ` ' or `-') separate symbols and words from each other. Typically, whitespace characters have no other syntactic use, and multiple whitespace characters are syntactically equivalent to one. Space, tab, newline and formfeed are almost always considered whitespace. -- Syntax class: word constituent "Word constituents" (designated with `w') are parts of normal English words and are typically used in variable and command names in programs. All upper and lower case letters and the digits are typically word constituents. -- Syntax class: symbol constituent "Symbol constituents" (designated with `_') are the extra characters that are used in variable and command names along with word constituents. For example, the symbol constituents class is used in Lisp mode to indicate that certain characters may be part of symbol names even though they are not part of English words. These characters are `$&*+-_<>'. In standard C, the only non-word-constituent character that is valid in symbols is underscore (`_'). -- Syntax class: punctuation character "Punctuation characters" (`.') are those characters that are used as punctuation in English, or are used in some way in a programming language to separate symbols from one another. Most programming language modes, including Emacs Lisp mode, have no characters in this class since the few characters that are not symbol or word constituents all have other uses. -- Syntax class: open parenthesis character -- Syntax class: close parenthesis character Open and close "parenthesis characters" are characters used in dissimilar pairs to surround sentences or expressions. Such a grouping is begun with an open parenthesis character and terminated with a close. Each open parenthesis character matches a particular close parenthesis character, and vice versa. Normally, Emacs indicates momentarily the matching open parenthesis when you insert a close parenthesis. *Note Blinking::. The class of open parentheses is designated with `(', and that of close parentheses with `)'. In English text, and in C code, the parenthesis pairs are `()', `[]', and `{}'. In Emacs Lisp, the delimiters for lists and vectors (`()' and `[]') are classified as parenthesis characters. -- Syntax class: string quote "String quote characters" (designated with `"') is used to delimit string constants in many languages, including Lisp and C. The same string quote character appears at the beginning and the end of a string. Such quoted strings do not nest. The parsing facilities of Emacs consider a string as a single token. The usual syntactic meanings of the characters in the string are suppressed. The Lisp modes have two string quote characters: double-quote (`"') and vertical bar (`|'). `|' is not used in Emacs Lisp, but it is used in Common Lisp. C also has two string quote characters: double-quote for strings, and single-quote (`'') for character constants. English text has no string quote characters because English is not a programming language. Although quotation marks are used in English, we do not want them to turn off the usual syntactic properties of other characters in the quotation. -- Syntax class: escape An "escape character" (designated with `\') starts an escape sequence such as is used in C string and character constants. The character `\' belongs to this class in both C and Lisp. (In C, it is used thus only inside strings, but it turns out to cause no trouble to treat it this way throughout C code.) -- Syntax class: character quote A "character quote character" (designated with `/') quotes the following character so that it loses its normal syntactic meaning. This differs from an escape character in that only the character immediately following is ever affected. This class is not currently used in any standard Emacs modes. -- Syntax class: paired delimiter "Paired delimiter characters" (designated with `$') are like string quote characters except that the syntactic properties of the characters between the delimiters are not suppressed. Only TeX mode uses a paired identical delimiter presently--the `$' that begins and ends math mode. -- Syntax class: expression prefix An "expression prefix operator" (designated with `'') is used for syntactic operators that are part of an expression if they appear next to one but are not part of an adjoining symbol. These characters in Lisp include the apostrophe, `'' (used for quoting), and the comma, `,' (used in macros). -- Syntax class: comment starter -- Syntax class: comment ender The "comment starter" and "comment ender" characters are used in different languages to delimit comments. These classes are designated with `<' and `>', respectively. English text has no comment characters. In Lisp, the semi-colon (`;') starts a comment and a newline or formfeed ends one. File: elisp, Node: Syntax Flags, Prev: Syntax Class Table, Up: Syntax Descriptors Syntax Flags ------------ In addition to the classes, entries for characters in a syntax table can include flags. There are four possible flags, represented by the characters `1', `2', `3', and `4'. All are used to describe multi-character comment delimiters. A flag indicates that the character for which the entry is being made can *also* be part of a comment sequence, in addition to the syntactic properties associated with its character class. The flags are independent of the class and each other for the sake of characters such as `*' in C mode, which is a punctuation character, *and* the second character of a start-of-comment sequence (`/*'), *and* the first character of an end-of-comment sequence (`*/'). The flags for a character C are: * `1' means C is the start of a two-character comment start sequence. * `2' means C is the second character of such a sequence. * `3' means C is the start of a two-character comment end sequence. * `4' means C is the second character of such a sequence. File: elisp, Node: Syntax Table Functions, Next: Parsing Expressions, Prev: Syntax Descriptors, Up: Syntax Tables Syntax Table Functions ====================== In this section we describe functions for creating, accessing and altering syntax tables. -- Function: make-syntax-table &optional TABLE This function constructs a copy of TABLE and returns it. If TABLE is not supplied (or is `nil'), it returns a copy of the current syntax table. Otherwise, an error is signaled if TABLE is not a syntax table. -- Function: copy-syntax-table &optional TABLE This function is identical to `make-syntax-table'. -- Command: modify-syntax-entry CHAR SYNTAX-DESCRIPTOR &optional TABLE This function sets the syntax entry for CHAR according to SYNTAX-DESCRIPTOR. The syntax is changed only for TABLE, which defaults to the current buffer's syntax table, and not in any other syntax table. The argument SYNTAX-DESCRIPTOR specifies the desired syntax; this is a string beginning with a class designator character, and optionally containing a matching character and flags as well. *Note Syntax Descriptors::. This function always returns `nil'. The old syntax information in the table for this character is discarded. An error is signaled if the first character of the syntax descriptor is not one of the twelve syntax class designator characters. An error is also signaled if CHAR is not a character. Examples: ;; Put the space character in class whitespace. (modify-syntax-entry ?\ " ") => nil ;; Make `$' an open parenthesis character, ;; with `^' as its matching close. (modify-syntax-entry ?$ "(^") => nil ;; Make `^' a close parenthesis character, ;; with `$' as its matching open. (modify-syntax-entry ?^ ")$") => nil ;; Make `/' a punctuation character, ;; the first character of a start-comment sequence, ;; and the second character of an end-comment sequence. ;; This is used in C mode. (modify-syntax-entry ?/ ".13") => nil -- Function: char-syntax CHARACTER This function returns the syntax class of CHARACTER, represented by its mnemonic designator character. This *only* returns the class, not any matching parenthesis or flags. An error is signaled if CHAR is not a character. The first example shows that the syntax class of space is whitespace (represented by a space). The second example shows that the syntax of `/' is punctuation in C-mode. This does not show the fact that it is also a comment sequence character. The third example shows that open parenthesis is in the class of open parentheses. This does not show the fact that it has a matching character, `)'. (char-to-string (char-syntax ?\ )) => " " (char-to-string (char-syntax ?/)) => "." (char-to-string (char-syntax ?\()) => "(" -- Function: set-syntax-table TABLE This function makes TABLE the syntax table for the current buffer. It returns TABLE. -- Function: syntax-table This function returns the current syntax table, which is the table for the current buffer. -- command: describe-syntax This function describes the syntax specifications of the current syntax table. It makes a listing in the `*Help*' buffer, and then pops up a window to display it. It returns `nil'. A portion of a description is shown here: (describe-syntax) => nil ---------- Buffer: *Help* ---------- C-q \ which means: escape C-r .. C-_ which means: whitespace ! . which means: punctuation ( () which means: open, matches ) ) )( which means: close, matches ( * .. + _ which means: symbol , . which means: punctuation - _ which means: symbol . . which means: punctuation / . 13 which means: punctuation, is the first character of a comment-start sequence, is the first character of a comment-end sequence 0 .. 9 w which means: word ---------- Buffer: *Help* ---------- File: elisp, Node: Parsing Expressions, Next: Standard Syntax Tables, Prev: Syntax Table Functions, Up: Syntax Tables Parsing and Moving Over Balanced Expressions ============================================ Here are several functions for parsing and scanning balanced expressions. The syntax table controls the interpretation of characters, so these functions can be used for Lisp expressions when in Lisp mode and for C expressions when in C mode. *Note List Motion::, for convenient higher-level functions for moving over balanced expressions. -- Function: parse-partial-sexp START LIMIT &optional TARGET-DEPTH STOP-BEFORE STATE This function parses an expression in the current buffer starting at START, not scanning past LIMIT. Parsing stops at LIMIT or when certain criteria described below are met; point is set to the location where parsing stops. The value returned is a description of the status of the parse at the point where it stops. Normally, START is assumed to be the top level of an expression to be parsed, such as the beginning of a function definition. Alternatively, you might wish to resume parsing in the middle of an expression. To do this, you must provide a STATE argument that describes the initial status of parsing. If STATE is omitted (or `nil'), parsing assumes that START is the beginning of a new parse at level 0. If the third argument TARGET-DEPTH is non-`nil', parsing stops if the depth in parentheses becomes equal to TARGET-DEPTH. The depth starts at 0, or at whatever is given in STATE. If the fourth argument STOP-BEFORE is non-`nil', parsing stops when it comes to any character that starts a sexp. The fifth argument STATE is a seven-element list of the same form as the value of this function, described below. The return value of one call may be used to initialize the state of the parse on another call to `parse-partial-sexp'. The result is a list of seven elements describing the final state of the parse: 1. The depth in parentheses, starting at 0. 2. The character position of the start of the innermost containing parenthetical grouping; `nil' if none. 3. The character position of the start of the last complete subexpression terminated; `nil' if none. 4. Non-`nil' if inside a string. (It is the character that will terminate the string.) 5. `t' if inside a comment. 6. `t' if point is just after a quote character. 7. The minimum parenthesis depth encountered during this scan. Elements 1, 4, 5, and 6 are significant in the argument STATE. This function is used to determine how to indent lines in programs written in languages that have nested parentheses. -- Function: scan-lists FROM COUNT DEPTH This function scans forward COUNT balanced parenthetical groupings from character number FROM. It returns the character number of the position thus found. If DEPTH is nonzero, parenthesis depth counting begins from that value. The only candidates for stopping are places where the depth in parentheses becomes zero; `scan-lists' counts COUNT such places and then stops. Thus, a positive value for DEPTH means go out levels of parenthesis. Comments are ignored if `parse-sexp-ignore-comments' is non-`nil'. If the beginning or end of the buffer (or its accessible portion) is reached and the depth is not zero, an `end-of-file' error is signaled. If the depth is zero but the count is not used up, `nil' is returned. -- Function: scan-sexps FROM COUNT Scan from character number FROM by COUNT balanced expressions. It returns the character number of the position thus found. Comments are ignored if `parse-sexp-ignore-comments' is non-`nil'. If the beginning or end of (the accessible part of) the buffer is reached in the middle of a parenthetical grouping, an `end-of-file' error is signaled. If the beginning or end is reached between groupings but before count is used up, `nil' is returned. -- Function: backward-prefix-chars This function moves point backward over any number of chars with expression prefix syntax. -- Variable: parse-sexp-ignore-comments If the value is non-`nil', then comments are treated as whitespace by the functions in this section and by `forward-sexp'. This works only when the comment terminator is something like `*/', and appears only to end a comment. If comments are terminated by newlines, you must make this variable `nil', since not every newline is the end of a comment. (In version 19, this limitation is removed.) File: elisp, Node: Standard Syntax Tables, Next: Syntax Table Internals, Prev: Parsing Expressions, Up: Syntax Tables Some Standard Syntax Tables =========================== Each of the major modes in Emacs has its own syntax table. Here are several of them: -- Function: standard-syntax-table This function returns the standard syntax table, which is the syntax table used in Fundamental mode. -- Variable: text-mode-syntax-table The value of this variable is the syntax table used in Text mode. -- Variable: c-mode-syntax-table The value of this variable is the syntax table in use in C-mode buffers. -- Variable: emacs-lisp-mode-syntax-table The value of this variable is the syntax table used in Emacs Lisp mode by editing commands. (It has no effect on the Lisp `read' function.) File: elisp, Node: Syntax Table Internals, Prev: Standard Syntax Tables, Up: Syntax Tables Syntax Table Internals ====================== Each element of a syntax table is an integer that translates into the full meaning of the entry: class, possible matching character, and flags. However, it is not common for a programmer to work with the entries directly in this form since the Lisp-level syntax table functions usually work with syntax descriptors (*note Syntax Descriptors::.). The low 8 bits of each element of a syntax table indicates the syntax class. Integer Class 0 whitespace 1 punctuation 2 word 3 symbol 4 open parenthesis 5 close parenthesis 6 expression prefix 7 string quote 8 paired delimiter 9 escape 10 character quote 11 comment-start 12 comment-end The next 8 bits are the matching opposite parenthesis (if the character has parenthesis syntax); otherwise, they are not meaningful. The next 4 bits are the flags. File: elisp, Node: Abbrevs, Next: Processes, Prev: Syntax Tables, Up: Top Abbrevs And Abbrev Expansion **************************** An abbreviation or "abbrev" is a string of characters that may be expanded to a longer string. The user can insert the abbrev string and find it replaced automatically with the expansion of the abbrev. This saves typing. The set of abbrevs currently in effect is recorded in an "abbrev table". Each buffer has a local abbrev table, but normally all buffers in the same major mode share one abbrev table. There is also a global abbrev table. Normally both are used. An abbrev table is represented as an obarray containing a symbol for each abbreviation. The symbol's name is the abbreviation. Its value is the expansion; its function definition is the hook; its property list cell contains the use count, the number of times the abbreviation has been expanded. Because these symbols are not inturned in the usual obarray, they will never appear as the result of reading a Lisp expression; in fact, they will never be used except by the code that handles abbrevs. Therefore, it is safe to use them in an extremely nonstandard way. *Note Creating Symbols::. For the user-level commands for abbrevs, see *Note Abbrev Mode: (emacs)Abbrevs. * Menu: * Abbrev Mode:: Setting up Emacs for abbreviation. * Tables: Abbrev Tables. Creating and working with abbrev tables. * Defining Abbrevs:: Specifying abbreviations and their expansions. * Files: Abbrev Files. Saving abbrevs in files. * Expansion: Abbrev Expansion. Controlling expansion; expansion subroutines. * Standard Abbrev Tables:: Abbrev tables used by various major modes. File: elisp, Node: Abbrev Mode, Next: Abbrev Tables, Prev: Abbrevs, Up: Abbrevs Setting Up Abbrev Mode ====================== Abbrev mode is a minor mode controlled by the value of the variable `abbrev-mode'. -- Variable: abbrev-mode A non-`nil' value of this variable turns on the automatic expansion of abbrevs when their abbreviations are inserted into a buffer. If the value is `nil', abbrevs may be defined, but they are not expanded automatically. This variable automatically becomes local when set in any fashion. -- Variable: default-abbrev-mode This is the value `abbrev-mode' for buffers that do not override it. This is the same as `(default-value 'abbrev-mode)'. File: elisp, Node: Abbrev Tables, Next: Defining Abbrevs, Prev: Abbrev Mode, Up: Abbrevs Abbrev Tables ============= This section describes how to create and manipulate abbrev tables. -- Function: make-abbrev-table This function creates and returns a new, empty abbrev table--an obarray containing no symbols. It is a vector filled with `nil's. -- Function: clear-abbrev-table TABLE This function undefines all the abbrevs in abbrev table TABLE, leaving it empty. The function returns `nil'. -- Function: define-abbrev-table TABNAME DEFINITIONS This function defines TABNAME (a symbol) as an abbrev table name, i.e., as a variable whose value is an abbrev table. It defines abbrevs in the table according to DEFINITIONS, a list of elements of the form `(ABBREVNAME EXPANSION HOOK USECOUNT)'. The value is always `nil'. -- Variable: abbrev-table-name-list This is a list of symbols whose values are abbrev tables. `define-abbrev-table' adds the new abbrev table name to this list. -- Function: insert-abbrev-table-description NAME HUMAN This function inserts before point a description of the abbrev table named NAME. The argument NAME is a symbol whose value is an abbrev table. The value is always `nil'. If HUMAN is non-`nil', a human-oriented description is inserted. Otherwise the description is a Lisp expression--a call to `define-abbrev-table' which would define NAME exactly as it is currently defined. File: elisp, Node: Defining Abbrevs, Next: Abbrev Files, Prev: Abbrev Tables, Up: Abbrevs Defining Abbrevs ================ These functions define an abbrev in a specified abbrev table. `define-abbrev' is the low-level basic function, while `add-abbrev' is used by commands that ask for information from the user. -- Function: add-abbrev TABLE TYPE ARG This function adds an abbreviation to abbrev table TABLE. The argument TYPE is a string describing in English the kind of abbrev this will be (typically, `"global"' or `"mode-specific"'); this is used in prompting the user. The argument ARG is the number of words in the expansion. The return value is the symbol which internally represents the new abbrev, or `nil' if the user declines to redefine an existing abbrev. -- Function: define-abbrev TABLE NAME EXPANSION HOOK This function defines an abbrev in TABLE named NAME, to expand to EXPANSION, and call HOOK. The return value is an uninterned symbol which represents the abbrev inside Emacs; its name is NAME. The argument NAME should be a string. The argument EXPANSION should be a string, or `nil', to undefine the abbrev. The argument HOOK is a function or `nil'. If HOOK is non-`nil', then it is called with no arguments after the abbrev is replaced with EXPANSION; point is located at the end of EXPANSION. The use count of the abbrev is initialized to zero. -- User Option: only-global-abbrevs If this variable is non-`nil', it means that the user plans to use global abbrevs only. This tells the commands that define mode-specific abbrevs to define global ones instead. This variable does not alter the functioning of the functions in this section; it is examined by their callers. File: elisp, Node: Abbrev Files, Next: Abbrev Expansion, Prev: Defining Abbrevs, Up: Abbrevs Saving Abbrevs in Files ======================= A file of saved abbrev definitions is actually a file of Lisp code. The abbrevs are saved in the form of a Lisp program to define the same abbrev tables with the same contents. Therefore, you can load the file with `load' (*note How Programs Do Loading::.). However, the function `quietly-read-abbrev-file' is provided as a more convenient interface. User-level facilities such as `save-some-buffers' can save abbrevs in a file automatically, under the control of variables described here. -- User Option: abbrev-file-name This is the default file name for reading and saving abbrevs. -- Function: quietly-read-abbrev-file FILENAME This function reads abbrev definitions from a file named FILENAME, previously written with `write-abbrev-file'. If FILENAME is `nil', the file specified in `abbrev-file-name' is used. `save-abbrevs' is set to `t' so that changes will be saved. This function does not display any messages. It returns `nil'. -- User Option: save-abbrevs A non-`nil' value for `save-abbrev' means that Emacs should save abbrevs when files are saved. `abbrev-file-name' specifies the file to save the abbrevs in. -- Variable: abbrevs-changed This variable is set non-`nil' by defining or altering any abbrevs. This serves as a flag for various Emacs commands to offer to save your abbrevs. -- Command: write-abbrev-file FILENAME Save all abbrev definitions, in all abbrev tables, in the file FILENAME as a Lisp program which will define the same abbrevs when loaded. This function returns `nil'. File: elisp, Node: Abbrev Expansion, Next: Standard Abbrev Tables, Prev: Abbrev Files, Up: Abbrevs Looking Up and Expanding Abbreviations ====================================== Abbrevs are usually expanded by commands for interactive use, or automatically by `self-insert'. This section describes the subroutines used in writing such functions, as well as the variables they use for communication. -- Function: abbrev-symbol ABBREV TABLE This function returns the symbol representing the abbrev named ABBREV. The value returned is `nil' if that abbrev is not defined. The optional second argument TABLE is the abbrev table to look it up in. By default, this function tries first the current buffer's local abbrev table, and second the global abbrev table. -- User Option: abbrev-all-caps When this is set non-`nil', an abbrev entered entirely in upper case is expanded using all upper case. Otherwise, an abbrev entered entirely in upper case is expanded by capitalizing each word of the expansion. -- Function: abbrev-expansion ABBREV &optional TABLE This function returns the string that ABBREV would expand into (as defined by the abbrev tables used for the current buffer). The optional argument TABLE specifies the abbrev table to use; if it is specified, the abbrev is looked up in that table only. -- Variable: abbrev-start-location This is the buffer position for `expand-abbrev' to use as the start of the next abbrev to be expanded. `nil' means use the word before point as the abbrev. `abbrev-start-location' is set to `nil' each time `expand-abbrev' is called. This variable is set by `abbrev-prefix-mark'. -- Variable: abbrev-start-location-buffer The value of this variable is the buffer for which `abbrev-start-location' has been set. Trying to expand an abbrev in any other buffer clears `abbrev-start-location'. This variable is set by `abbrev-prefix-mark'. -- Variable: last-abbrev This is the `abbrev-symbol' of the last abbrev expanded. This information is left by `expand-abbrev' for the sake of the `unexpand-abbrev' command. -- Variable: last-abbrev-location This is the location of the last abbrev expanded. This contains information left by `expand-abbrev' for the sake of the `unexpand-abbrev' command. -- Variable: last-abbrev-text This is the exact expansion text of the last abbrev expanded, as results from case conversion. Its value is `nil' if the abbrev has already been unexpanded. This contains information left by `expand-abbrev' for the sake of the `unexpand-abbrev' command. File: elisp, Node: Standard Abbrev Tables, Prev: Abbrev Expansion, Up: Abbrevs Standard Abbrev Tables ====================== Here we list the variables that hold the abbrev tables for the preloaded major modes of Emacs. -- Variable: global-abbrev-table This is the abbrev table for mode-independent abbrevs. The abbrevs defined in it apply to all buffers. Each buffer may also have a local abbrev table, whose abbrev definitions take precedence over those in the global table. -- Variable: local-abbrev-table The value of this buffer-local variable is the (mode-specific) abbreviation table of the current buffer. -- Variable: fundamental-mode-abbrev-table This is the local abbrev table used in Fundamental mode. It is the local abbrev table in all buffers in Fundamental mode. -- Variable: text-mode-abbrev-table This is the local abbrev table used in Text mode. -- Variable: c-mode-abbrev-table This is the local abbrev table used in C mode. -- Variable: lisp-mode-abbrev-table This is the local abbrev table used in Lisp mode and Emacs Lisp mode. 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. * 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. * VMS Subprocesses:: VMS has completely different subprocess features. * TCP:: Opening network connections. File: elisp, Node: Subprocess Creation, Next: Synchronous Processes, Prev: Processes, Up: Processes Functions that Create Subprocesses ================================== There are three functions that create a new Unix 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 program to be run is specified with the function's PROGRAM argument. An error is signaled if the file is not found or cannot be executed. The actual file containing the program is found by following normal Unix rules: if an absolute file name is given, then the program must be found in the specified file; if a relative file name is given, then the directories in `exec-path' are searched sequentially for a suitable file. The variable `exec-path' is initialized when Emacs is started, based on the value of the environment variable `PATH'. The standard Unix abbreviations, `~', `.', and `..', are interpreted as usual, 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', then the output will be discarded (by directing it to `/dev/null') unless a filter function is specified to handle it. (*Note Filter Functions::, and *Note Streams::.) Normally, you should avoid having multiple processes send output to the same buffer because the outputs will 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. *Note:* the argument PROGRAM contains only the name of the program; it may not contain any command-line arguments. Such arguments must be provided via ARGS. 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'. -- Variable: process-environment This variable is a list of strings to append to the environment of processes as they are created. Each string assigns a value to a shell environment variable. (This applies both to asynchronous and synchronous processes.) process-environment => ("l=/usr/stanford/lib/gnuemacs/lisp" "PATH=.:/user/lewis/bin:/usr/class:/nfsusr/local/bin" "USER=lewis" "TERM=ibmapa16" "SHELL=/bin/csh" "HOME=/user/lewis") -- 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 `loadst' is an example of such a program; it is used by the `display-time' command to print the current time (and certain other information) once per minute. The default value is the name of a directory whose name ends in `etc'. We call the directory `emacs/etc', since its name usually ends that way. We sometimes refer to "the directory `emacs/etc'," when strictly speaking we ought to say, "the directory named by the variable `exec-directory'." Most of the time, there is no difference. -- 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: Asynchronous Processes, 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', and the process is killed by sending it a `SIGKILL' signal. *Note Quitting::. The synchronous subprocess functions return `nil' in version 18. In version 19, they will 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, the output is discarded and `call-process' returns immediately. 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 are supplied as the command line arguments for the program. The examples below are both run with the buffer `foo' 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 `dired-readin' function contains a good example of the use of `call-process': (call-process "ls" nil buffer nil dired-listing-switches dirname) -- 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', which may be useful when the output is going to be inserted back in the current buffer. If BUFFER-OR-NAME names a buffer, the output is inserted in that buffer at point. If BUFFER-OR-NAME is `t', the output is sent to the current buffer. If BUFFER-OR-NAME is `nil', the output is discarded. If BUFFER-OR-NAME is the integer 0, the output is discarded and `call-process' returns immediately, as in `call-process'. If DISPLAY is non-`nil', then `call-process-region' 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 are supplied as the command line arguments for the program. 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: Asynchronous Processes, Next: Deleting Processes, Prev: Synchronous Processes, Up: Processes Creating an Asynchronous Process ================================ After an "asynchronous process" is created, Emacs and the Lisp program can 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 for Emacs Lisp programs. 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 are supplied as the 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, 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" "/user/lewis/bin") => #<process my-process<1>> ---------- 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 ---------- -- 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 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 in order to change it for just one call of `start-process', temporarily rebind it with `let'. (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. The argument NAME may be a process, the name of a process, a buffer, or the name of a buffer. The subprocess is killed with a `SIGHUP' signal. (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. (Any processes listed as `Exited' or `Signaled' are actually eliminated after the listing is made.) This function returns `nil'. -- Function: process-list This function returns a list of all processes that have not been deleted. (process-list) => (#<process display-time> #<process shell>) -- 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") => #<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-exit-status PROCESS This function returns the exit status of PROCESS or the signal number that killed it. If PROCESS has not yet terminated, the value is 0. -- 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 either a process or a string. If it is a string, it need not name an actual process. 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. `nil' if PROCESS-NAME is not the name of an existing process. (process-status "shell") => run (process-status "never-existed") => nil x => #<process xx<1>> (process-status x) => exit For a network stream, `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'.