This is elisp, produced by makeinfo version 4.0f from ./elisp.texi. INFO-DIR-SECTION Editors START-INFO-DIR-ENTRY * Elisp: (elisp). The Emacs Lisp Reference Manual. END-INFO-DIR-ENTRY This Info file contains edition 2.8 of the GNU Emacs Lisp Reference Manual, corresponding to Emacs version 21.2. Published by the Free Software Foundation 59 Temple Place, Suite 330 Boston, MA 02111-1307 USA Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being "Copying", with the Front-Cover texts being "A GNU Manual", and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled "GNU Free Documentation License". (a) The FSF's Back-Cover Text is: "You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development."  File: elisp, Node: Regexp Special, Next: Char Classes, Up: Syntax of Regexps Special Characters in Regular Expressions ......................................... Here is a list of the characters that are special in a regular expression. `.' (Period) is a special character that matches any single character except a newline. Using concatenation, we can make regular expressions like `a.b', which matches any three-character string that begins with `a' and ends with `b'. `*' is not a construct by itself; it is a postfix operator that means to match the preceding regular expression repetitively as many times as possible. Thus, `o*' matches any number of `o's (including no `o's). `*' always applies to the _smallest_ possible preceding expression. Thus, `fo*' has a repeating `o', not a repeating `fo'. It matches `f', `fo', `foo', and so on. The matcher processes a `*' construct by matching, immediately, as many repetitions as can be found. Then it continues with the rest of the pattern. If that fails, backtracking occurs, discarding some of the matches of the `*'-modified construct in the hope that that will make it possible to match the rest of the pattern. For example, in matching `ca*ar' against the string `caaar', the `a*' first tries to match all three `a's; but the rest of the pattern is `ar' and there is only `r' left to match, so this try fails. The next alternative is for `a*' to match only two `a's. With this choice, the rest of the regexp matches successfully. Nested repetition operators can be extremely slow if they specify backtracking loops. For example, it could take hours for the regular expression `\(x+y*\)*a' to try to match the sequence `xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz', before it ultimately fails. The slowness is because Emacs must try each imaginable way of grouping the 35 `x's before concluding that none of them can work. To make sure your regular expressions run fast, check nested repetitions carefully. `+' is a postfix operator, similar to `*' except that it must match the preceding expression at least once. So, for example, `ca+r' matches the strings `car' and `caaaar' but not the string `cr', whereas `ca*r' matches all three strings. `?' is a postfix operator, similar to `*' except that it must match the preceding expression either once or not at all. For example, `ca?r' matches `car' or `cr'; nothing else. `*?', `+?', `??' These are "non-greedy" variants of the operators `*', `+' and `?'. Where those operators match the largest possible substring (consistent with matching the entire containing expression), the non-greedy variants match the smallest possible substring (consistent with matching the entire containing expression). For example, the regular expression `c[ad]*a' when applied to the string `cdaaada' matches the whole string; but the regular expression `c[ad]*?a', applied to that same string, matches just `cda'. (The smallest possible match here for `[ad]*?' that permits the whole expression to match is `d'.) `[ ... ]' is a "character alternative", which begins with `[' and is terminated by `]'. In the simplest case, the characters between the two brackets are what this character alternative can match. Thus, `[ad]' matches either one `a' or one `d', and `[ad]*' matches any string composed of just `a's and `d's (including the empty string), from which it follows that `c[ad]*r' matches `cr', `car', `cdr', `caddaar', etc. You can also include character ranges in a character alternative, by writing the starting and ending characters with a `-' between them. Thus, `[a-z]' matches any lower-case ASCII letter. Ranges may be intermixed freely with individual characters, as in `[a-z$%.]', which matches any lower case ASCII letter or `$', `%' or period. Note that the usual regexp special characters are not special inside a character alternative. A completely different set of characters is special inside character alternatives: `]', `-' and `^'. To include a `]' in a character alternative, you must make it the first character. For example, `[]a]' matches `]' or `a'. To include a `-', write `-' as the first or last character of the character alternative, or put it after a range. Thus, `[]-]' matches both `]' and `-'. To include `^' in a character alternative, put it anywhere but at the beginning. The beginning and end of a range of multibyte characters must be in the same character set (*note Character Sets::). Thus, `"[\x8e0-\x97c]"' is invalid because character 0x8e0 (`a' with grave accent) is in the Emacs character set for Latin-1 but the character 0x97c (`u' with diaeresis) is in the Emacs character set for Latin-2. (We use Lisp string syntax to write that example, and a few others in the next few paragraphs, in order to include hex escape sequences in them.) If a range starts with a unibyte character C and ends with a multibyte character C2, the range is divided into two parts: one is `C..?\377', the other is `C1..C2', where C1 is the first character of the charset to which C2 belongs. You cannot always match all non-ASCII characters with the regular expression `"[\200-\377]"'. This works when searching a unibyte buffer or string (*note Text Representations::), but not in a multibyte buffer or string, because many non-ASCII characters have codes above octal 0377. However, the regular expression `"[^\000-\177]"' does match all non-ASCII characters (see below regarding `^'), in both multibyte and unibyte representations, because only the ASCII characters are excluded. Starting in Emacs 21, a character alternative can also specify named character classes (*note Char Classes::). This is a POSIX feature whose syntax is `[:CLASS:]'. Using a character class is equivalent to mentioning each of the characters in that class; but the latter is not feasible in practice, since some classes include thousands of different characters. `[^ ... ]' `[^' begins a "complemented character alternative", which matches any character except the ones specified. Thus, `[^a-z0-9A-Z]' matches all characters _except_ letters and digits. `^' is not special in a character alternative unless it is the first character. The character following the `^' is treated as if it were first (in other words, `-' and `]' are not special there). A complemented character alternative can match a newline, unless newline is mentioned as one of the characters not to match. This is in contrast to the handling of regexps in programs such as `grep'. `^' is a special character that matches the empty string, but only at the beginning of a line in the text being matched. Otherwise it fails to match anything. Thus, `^foo' matches a `foo' that occurs at the beginning of a line. When matching a string instead of a buffer, `^' matches at the beginning of the string or after a newline character. For historical compatibility reasons, `^' can be used only at the beginning of the regular expression, or after `\(' or `\|'. `$' is similar to `^' but matches only at the end of a line. Thus, `x+$' matches a string of one `x' or more at the end of a line. When matching a string instead of a buffer, `$' matches at the end of the string or before a newline character. For historical compatibility reasons, `$' can be used only at the end of the regular expression, or before `\)' or `\|'. `\' has two functions: it quotes the special characters (including `\'), and it introduces additional special constructs. Because `\' quotes special characters, `\$' is a regular expression that matches only `$', and `\[' is a regular expression that matches only `[', and so on. Note that `\' also has special meaning in the read syntax of Lisp strings (*note String Type::), and must be quoted with `\'. For example, the regular expression that matches the `\' character is `\\'. To write a Lisp string that contains the characters `\\', Lisp syntax requires you to quote each `\' with another `\'. Therefore, the read syntax for a regular expression matching `\' is `"\\\\"'. *Please note:* For historical compatibility, special characters are treated as ordinary ones if they are in contexts where their special meanings make no sense. For example, `*foo' treats `*' as ordinary since there is no preceding expression on which the `*' can act. It is poor practice to depend on this behavior; quote the special character anyway, regardless of where it appears.  File: elisp, Node: Char Classes, Next: Regexp Backslash, Prev: Regexp Special, Up: Syntax of Regexps Character Classes ................. Here is a table of the classes you can use in a character alternative, in Emacs 21, and what they mean: `[:ascii:]' This matches any ASCII (unibyte) character. `[:alnum:]' This matches any letter or digit. (At present, for multibyte characters, it matches anything that has word syntax.) `[:alpha:]' This matches any letter. (At present, for multibyte characters, it matches anything that has word syntax.) `[:blank:]' This matches space and tab only. `[:cntrl:]' This matches any ASCII control character. `[:digit:]' This matches `0' through `9'. Thus, `[-+[:digit:]]' matches any digit, as well as `+' and `-'. `[:graph:]' This matches graphic characters--everything except ASCII control characters, space, and the delete character. `[:lower:]' This matches any lower-case letter, as determined by the current case table (*note Case Tables::). `[:nonascii:]' This matches any non-ASCII (multibyte) character. `[:print:]' This matches printing characters--everything except ASCII control characters and the delete character. `[:punct:]' This matches any punctuation character. (At present, for multibyte characters, it matches anything that has non-word syntax.) `[:space:]' This matches any character that has whitespace syntax (*note Syntax Class Table::). `[:upper:]' This matches any upper-case letter, as determined by the current case table (*note Case Tables::). `[:word:]' This matches any character that has word syntax (*note Syntax Class Table::). `[:xdigit:]' This matches the hexadecimal digits: `0' through `9', `a' through `f' and `A' through `F'.  File: elisp, Node: Regexp Backslash, Prev: Char Classes, Up: Syntax of Regexps Backslash Constructs in Regular Expressions ........................................... For the most part, `\' followed by any character matches only that character. However, there are several exceptions: certain two-character sequences starting with `\' that have special meanings. (The character after the `\' in such a sequence is always ordinary when used on its own.) Here is a table of the special `\' constructs. `\|' specifies an alternative. Two regular expressions A and B with `\|' in between form an expression that matches anything that either A or B matches. Thus, `foo\|bar' matches either `foo' or `bar' but no other string. `\|' applies to the largest possible surrounding expressions. Only a surrounding `\( ... \)' grouping can limit the grouping power of `\|'. Full backtracking capability exists to handle multiple uses of `\|', if you use the POSIX regular expression functions (*note POSIX Regexps::). `\{M\}' is a postfix operator that repeats the previous pattern exactly M times. Thus, `x\{5\}' matches the string `xxxxx' and nothing else. `c[ad]\{3\}r' matches string such as `caaar', `cdddr', `cadar', and so on. `\{M,N\}' is more general postfix operator that specifies repetition with a minimum of M repeats and a maximum of N repeats. If M is omitted, the minimum is 0; if N is omitted, there is no maximum. For example, `c[ad]\{1,2\}r' matches the strings `car', `cdr', `caar', `cadr', `cdar', and `cddr', and nothing else. `\{0,1\}' or `\{,1\}' is equivalent to `?'. `\{0,\}' or `\{,\}' is equivalent to `*'. `\{1,\}' is equivalent to `+'. `\( ... \)' is a grouping construct that serves three purposes: 1. To enclose a set of `\|' alternatives for other operations. Thus, the regular expression `\(foo\|bar\)x' matches either `foox' or `barx'. 2. To enclose a complicated expression for the postfix operators `*', `+' and `?' to operate on. Thus, `ba\(na\)*' matches `ba', `bana', `banana', `bananana', etc., with any number (zero or more) of `na' strings. 3. To record a matched substring for future reference with `\DIGIT' (see below). This last application is not a consequence of the idea of a parenthetical grouping; it is a separate feature that was assigned as a second meaning to the same `\( ... \)' construct because, in pratice, there was usually no conflict between the two meanings. But occasionally there is a conflict, and that led to the introduction of shy groups. `\(?: ... \)' is the "shy group" construct. A shy group serves the first two purposes of an ordinary group (controlling the nesting of other operators), but it does not get a number, so you cannot refer back to its value with `\DIGIT'. Shy groups are particulary useful for mechanically-constructed regular expressions because they can be added automatically without altering the numbering of any ordinary, non-shy groups. `\DIGIT' matches the same text that matched the DIGITth occurrence of a grouping (`\( ... \)') construct. In other words, after the end of a group, the matcher remembers the beginning and end of the text matched by that group. Later on in the regular expression you can use `\' followed by DIGIT to match that same text, whatever it may have been. The strings matching the first nine grouping constructs appearing in the entire regular expression passed to a search or matching function are assigned numbers 1 through 9 in the order that the open parentheses appear in the regular expression. So you can use `\1' through `\9' to refer to the text matched by the corresponding grouping constructs. For example, `\(.*\)\1' matches any newline-free string that is composed of two identical halves. The `\(.*\)' matches the first half, which may be anything, but the `\1' that follows must match the same exact text. If a particular grouping construct in the regular expression was never matched--for instance, if it appears inside of an alternative that wasn't used, or inside of a repetition that repeated zero times--then the corresponding `\DIGIT' construct never matches anything. To use an artificial example,, `\(foo\(b*\)\|lose\)\2' cannot match `lose': the second alternative inside the larger group matches it, but then `\2' is undefined and can't match anything. But it can match `foobb', because the first alternative matches `foob' and `\2' matches `b'. `\w' matches any word-constituent character. The editor syntax table determines which characters these are. *Note Syntax Tables::. `\W' matches any character that is not a word constituent. `\sCODE' matches any character whose syntax is CODE. Here CODE is a character that represents a syntax code: thus, `w' for word constituent, `-' for whitespace, `(' for open parenthesis, etc. To represent whitespace syntax, use either `-' or a space character. *Note Syntax Class Table::, for a list of syntax codes and the characters that stand for them. `\SCODE' matches any character whose syntax is not CODE. `\cC' matches any character whose category is C. Here C is a character that represents a category: thus, `c' for Chinese characters or `g' for Greek characters in the standard category table. `\CC' matches any character whose category is not C. The following regular expression constructs match the empty string--that is, they don't use up any characters--but whether they match depends on the context. `\`' matches the empty string, but only at the beginning of the buffer or string being matched against. `\'' matches the empty string, but only at the end of the buffer or string being matched against. `\=' matches the empty string, but only at point. (This construct is not defined when matching against a string.) `\b' matches the empty string, but only at the beginning or end of a word. Thus, `\bfoo\b' matches any occurrence of `foo' as a separate word. `\bballs?\b' matches `ball' or `balls' as a separate word. `\b' matches at the beginning or end of the buffer regardless of what text appears next to it. `\B' matches the empty string, but _not_ at the beginning or end of a word. `\<' matches the empty string, but only at the beginning of a word. `\<' matches at the beginning of the buffer only if a word-constituent character follows. `\>' matches the empty string, but only at the end of a word. `\>' matches at the end of the buffer only if the contents end with a word-constituent character. Not every string is a valid regular expression. For example, a string with unbalanced square brackets is invalid (with a few exceptions, such as `[]]'), and so is a string that ends with a single `\'. If an invalid regular expression is passed to any of the search functions, an `invalid-regexp' error is signaled.  File: elisp, Node: Regexp Example, Prev: Regexp Functions, Up: Regular Expressions Complex Regexp Example ---------------------- Here is a complicated regexp, used by Emacs to recognize the end of a sentence together with any whitespace that follows. It is the value of the variable `sentence-end'. First, we show the regexp as a string in Lisp syntax to distinguish spaces from tab characters. The string constant begins and ends with a double-quote. `\"' stands for a double-quote as part of the string, `\\' for a backslash as part of the string, `\t' for a tab and `\n' for a newline. "[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*" In contrast, if you evaluate the variable `sentence-end', you will see the following: sentence-end => "[.?!][]\"')}]*\\($\\| $\\| \\| \\)[ ]*" In this output, tab and newline appear as themselves. This regular expression contains four parts in succession and can be deciphered as follows: `[.?!]' The first part of the pattern is a character alternative that matches any one of three characters: period, question mark, and exclamation mark. The match must begin with one of these three characters. `[]\"')}]*' The second part of the pattern matches any closing braces and quotation marks, zero or more of them, that may follow the period, question mark or exclamation mark. The `\"' is Lisp syntax for a double-quote in a string. The `*' at the end indicates that the immediately preceding regular expression (a character alternative, in this case) may be repeated zero or more times. `\\($\\| $\\|\t\\| \\)' The third part of the pattern matches the whitespace that follows the end of a sentence: the end of a line (optionally with a space), or a tab, or two spaces. The double backslashes mark the parentheses and vertical bars as regular expression syntax; the parentheses delimit a group and the vertical bars separate alternatives. The dollar sign is used to match the end of a line. `[ \t\n]*' Finally, the last part of the pattern matches any additional whitespace beyond the minimum needed to end a sentence.  File: elisp, Node: Regexp Functions, Next: Regexp Example, Prev: Syntax of Regexps, Up: Regular Expressions Regular Expression Functions ---------------------------- These functions operate on regular expressions. - Function: regexp-quote string This function returns a regular expression whose only exact match is STRING. Using this regular expression in `looking-at' will succeed only if the next characters in the buffer are STRING; using it in a search function will succeed if the text being searched contains STRING. This allows you to request an exact string match or search when calling a function that wants a regular expression. (regexp-quote "^The cat$") => "\\^The cat\\$" One use of `regexp-quote' is to combine an exact string match with context described as a regular expression. For example, this searches for the string that is the value of STRING, surrounded by whitespace: (re-search-forward (concat "\\s-" (regexp-quote string) "\\s-")) - Function: regexp-opt strings &optional paren This function returns an efficient regular expression that will match any of the strings STRINGS. This is useful when you need to make matching or searching as fast as possible--for example, for Font Lock mode. If the optional argument PAREN is non-`nil', then the returned regular expression is always enclosed by at least one parentheses-grouping construct. This simplified definition of `regexp-opt' produces a regular expression which is equivalent to the actual value (but not as efficient): (defun regexp-opt (strings paren) (let ((open-paren (if paren "\\(" "")) (close-paren (if paren "\\)" ""))) (concat open-paren (mapconcat 'regexp-quote strings "\\|") close-paren))) - Function: regexp-opt-depth regexp This function returns the total number of grouping constructs (parenthesized expressions) in REGEXP.  File: elisp, Node: Regexp Search, Next: POSIX Regexps, Prev: Regular Expressions, Up: Searching and Matching Regular Expression Searching ============================ In GNU Emacs, you can search for the next match for a regular expression either incrementally or not. For incremental search commands, see *Note Regular Expression Search: (emacs)Regexp Search. Here we describe only the search functions useful in programs. The principal one is `re-search-forward'. These search functions convert the regular expression to multibyte if the buffer is multibyte; they convert the regular expression to unibyte if the buffer is unibyte. *Note Text Representations::. - Command: re-search-forward regexp &optional limit noerror repeat This function searches forward in the current buffer for a string of text that is matched by the regular expression REGEXP. The function skips over any amount of text that is not matched by REGEXP, and leaves point at the end of the first match found. It returns the new value of point. If LIMIT is non-`nil' (it must be a position in the current buffer), then it is the upper bound to the search. No match extending after that position is accepted. If REPEAT is supplied (it must be a positive number), then the search is repeated that many times (each time starting at the end of the previous time's match). If all these successive searches succeed, the function succeeds, moving point and returning its new value. Otherwise the function fails. What happens when the function fails depends on the value of NOERROR. If NOERROR is `nil', a `search-failed' error is signaled. If NOERROR is `t', `re-search-forward' does nothing and returns `nil'. If NOERROR is neither `nil' nor `t', then `re-search-forward' moves point to LIMIT (or the end of the buffer) and returns `nil'. In the following example, point is initially before the `T'. Evaluating the search call moves point to the end of that line (between the `t' of `hat' and the newline). ---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (re-search-forward "[a-z]+" nil t 5) => 27 ---------- Buffer: foo ---------- I read "The cat in the hat-!- comes back" twice. ---------- Buffer: foo ---------- - Command: re-search-backward regexp &optional limit noerror repeat This function searches backward in the current buffer for a string of text that is matched by the regular expression REGEXP, leaving point at the beginning of the first text found. This function is analogous to `re-search-forward', but they are not simple mirror images. `re-search-forward' finds the match whose beginning is as close as possible to the starting point. If `re-search-backward' were a perfect mirror image, it would find the match whose end is as close as possible. However, in fact it finds the match whose beginning is as close as possible. The reason for this is that matching a regular expression at a given spot always works from beginning to end, and starts at a specified beginning position. A true mirror-image of `re-search-forward' would require a special feature for matching regular expressions from end to beginning. It's not worth the trouble of implementing that. - Function: string-match regexp string &optional start This function returns the index of the start of the first match for the regular expression REGEXP in STRING, or `nil' if there is no match. If START is non-`nil', the search starts at that index in STRING. For example, (string-match "quick" "The quick brown fox jumped quickly.") => 4 (string-match "quick" "The quick brown fox jumped quickly." 8) => 27 The index of the first character of the string is 0, the index of the second character is 1, and so on. After this function returns, the index of the first character beyond the match is available as `(match-end 0)'. *Note Match Data::. (string-match "quick" "The quick brown fox jumped quickly." 8) => 27 (match-end 0) => 32 - Function: looking-at regexp This function determines whether the text in the current buffer directly following point matches the regular expression REGEXP. "Directly following" means precisely that: the search is "anchored" and it can succeed only starting with the first character following point. The result is `t' if so, `nil' otherwise. This function does not move point, but it updates the match data, which you can access using `match-beginning' and `match-end'. *Note Match Data::. In this example, point is located directly before the `T'. If it were anywhere else, the result would be `nil'. ---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (looking-at "The cat in the hat$") => t  File: elisp, Node: POSIX Regexps, Next: Search and Replace, Prev: Regexp Search, Up: Searching and Matching POSIX Regular Expression Searching ================================== The usual regular expression functions do backtracking when necessary to handle the `\|' and repetition constructs, but they continue this only until they find _some_ match. Then they succeed and report the first match found. This section describes alternative search functions which perform the full backtracking specified by the POSIX standard for regular expression matching. They continue backtracking until they have tried all possibilities and found all matches, so they can report the longest match, as required by POSIX. This is much slower, so use these functions only when you really need the longest match. - Function: posix-search-forward regexp &optional limit noerror repeat This is like `re-search-forward' except that it performs the full backtracking specified by the POSIX standard for regular expression matching. - Function: posix-search-backward regexp &optional limit noerror repeat This is like `re-search-backward' except that it performs the full backtracking specified by the POSIX standard for regular expression matching. - Function: posix-looking-at regexp This is like `looking-at' except that it performs the full backtracking specified by the POSIX standard for regular expression matching. - Function: posix-string-match regexp string &optional start This is like `string-match' except that it performs the full backtracking specified by the POSIX standard for regular expression matching.  File: elisp, Node: Search and Replace, Next: Match Data, Prev: POSIX Regexps, Up: Searching and Matching Search and Replace ================== - Function: perform-replace from-string replacements start end query-flag regexp-flag delimited-flag &optional repeat-count map This function is the guts of `query-replace' and related commands. It searches for occurrences of FROM-STRING in the text between positions START and END and replaces some or all of them. If START is `nil', point is used instead, and the buffer's end is used for END. If QUERY-FLAG is `nil', it replaces all occurrences; otherwise, it asks the user what to do about each one. If REGEXP-FLAG is non-`nil', then FROM-STRING is considered a regular expression; otherwise, it must match literally. If DELIMITED-FLAG is non-`nil', then only replacements surrounded by word boundaries are considered. The argument REPLACEMENTS specifies what to replace occurrences with. If it is a string, that string is used. It can also be a list of strings, to be used in cyclic order. If REPLACEMENTS is a cons cell, `(FUNCTION . DATA)', this means to call FUNCTION after each match to get the replacement text. This function is called with two arguments: DATA, and the number of replacements already made. If REPEAT-COUNT is non-`nil', it should be an integer. Then it specifies how many times to use each of the strings in the REPLACEMENTS list before advancing cyclicly to the next one. If FROM-STRING contains upper-case letters, then `perform-replace' binds `case-fold-search' to `nil', and it uses the `replacements' without altering the case of them. Normally, the keymap `query-replace-map' defines the possible user responses for queries. The argument MAP, if non-`nil', is a keymap to use instead of `query-replace-map'. - Variable: query-replace-map This variable holds a special keymap that defines the valid user responses for `query-replace' and related functions, as well as `y-or-n-p' and `map-y-or-n-p'. It is unusual in two ways: * The "key bindings" are not commands, just symbols that are meaningful to the functions that use this map. * Prefix keys are not supported; each key binding must be for a single-event key sequence. This is because the functions don't use `read-key-sequence' to get the input; instead, they read a single event and look it up "by hand." Here are the meaningful "bindings" for `query-replace-map'. Several of them are meaningful only for `query-replace' and friends. `act' Do take the action being considered--in other words, "yes." `skip' Do not take action for this question--in other words, "no." `exit' Answer this question "no," and give up on the entire series of questions, assuming that the answers will be "no." `act-and-exit' Answer this question "yes," and give up on the entire series of questions, assuming that subsequent answers will be "no." `act-and-show' Answer this question "yes," but show the results--don't advance yet to the next question. `automatic' Answer this question and all subsequent questions in the series with "yes," without further user interaction. `backup' Move back to the previous place that a question was asked about. `edit' Enter a recursive edit to deal with this question--instead of any other action that would normally be taken. `delete-and-edit' Delete the text being considered, then enter a recursive edit to replace it. `recenter' Redisplay and center the window, then ask the same question again. `quit' Perform a quit right away. Only `y-or-n-p' and related functions use this answer. `help' Display some help, then ask again.  File: elisp, Node: Match Data, Next: Searching and Case, Prev: Search and Replace, Up: Searching and Matching The Match Data ============== Emacs keeps track of the start and end positions of the segments of text found during a regular expression search. This means, for example, that you can search for a complex pattern, such as a date in an Rmail message, and then extract parts of the match under control of the pattern. Because the match data normally describe the most recent search only, you must be careful not to do another search inadvertently between the search you wish to refer back to and the use of the match data. If you can't avoid another intervening search, you must save and restore the match data around it, to prevent it from being overwritten. * Menu: * Replacing Match:: Replacing a substring that was matched. * Simple Match Data:: Accessing single items of match data, such as where a particular subexpression started. * Entire Match Data:: Accessing the entire match data at once, as a list. * Saving Match Data:: Saving and restoring the match data.  File: elisp, Node: Replacing Match, Next: Simple Match Data, Up: Match Data Replacing the Text that Matched ------------------------------- This function replaces the text matched by the last search with REPLACEMENT. - Function: replace-match replacement &optional fixedcase literal string subexp This function replaces the text in the buffer (or in STRING) that was matched by the last search. It replaces that text with REPLACEMENT. If you did the last search in a buffer, you should specify `nil' for STRING. Then `replace-match' does the replacement by editing the buffer; it leaves point at the end of the replacement text, and returns `t'. If you did the search in a string, pass the same string as STRING. Then `replace-match' does the replacement by constructing and returning a new string. If FIXEDCASE is non-`nil', then the case of the replacement text is not changed; otherwise, the replacement text is converted to a different case depending upon the capitalization of the text to be replaced. If the original text is all upper case, the replacement text is converted to upper case. If the first word of the original text is capitalized, then the first word of the replacement text is capitalized. If the original text contains just one word, and that word is a capital letter, `replace-match' considers this a capitalized first word rather than all upper case. If LITERAL is non-`nil', then REPLACEMENT is inserted exactly as it is, the only alterations being case changes as needed. If it is `nil' (the default), then the character `\' is treated specially. If a `\' appears in REPLACEMENT, then it must be part of one of the following sequences: `\&' `\&' stands for the entire text being replaced. `\N' `\N', where N is a digit, stands for the text that matched the Nth subexpression in the original regexp. Subexpressions are those expressions grouped inside `\(...\)'. `\\' `\\' stands for a single `\' in the replacement text. If SUBEXP is non-`nil', that says to replace just subexpression number SUBEXP of the regexp that was matched, not the entire match. For example, after matching `foo \(ba*r\)', calling `replace-match' with 1 as SUBEXP means to replace just the text that matched `\(ba*r\)'.  File: elisp, Node: Simple Match Data, Next: Entire Match Data, Prev: Replacing Match, Up: Match Data Simple Match Data Access ------------------------ This section explains how to use the match data to find out what was matched by the last search or match operation. You can ask about the entire matching text, or about a particular parenthetical subexpression of a regular expression. The COUNT argument in the functions below specifies which. If COUNT is zero, you are asking about the entire match. If COUNT is positive, it specifies which subexpression you want. Recall that the subexpressions of a regular expression are those expressions grouped with escaped parentheses, `\(...\)'. The COUNTth subexpression is found by counting occurrences of `\(' from the beginning of the whole regular expression. The first subexpression is numbered 1, the second 2, and so on. Only regular expressions can have subexpressions--after a simple string search, the only information available is about the entire match. A search which fails may or may not alter the match data. In the past, a failing search did not do this, but we may change it in the future. - Function: match-string count &optional in-string This function returns, as a string, the text matched in the last search or match operation. It returns the entire text if COUNT is zero, or just the portion corresponding to the COUNTth parenthetical subexpression, if COUNT is positive. If the last such operation was done against a string with `string-match', then you should pass the same string as the argument IN-STRING. After a buffer search or match, you should omit IN-STRING or pass `nil' for it; but you should make sure that the current buffer when you call `match-string' is the one in which you did the searching or matching. The value is `nil' if COUNT is out of range, or for a subexpression inside a `\|' alternative that wasn't used or a repetition that repeated zero times. - Function: match-string-no-properties count &optional in-string This function is like `match-string' except that the result has no text properties. - Function: match-beginning count This function returns the position of the start of text matched by the last regular expression searched for, or a subexpression of it. If COUNT is zero, then the value is the position of the start of the entire match. Otherwise, COUNT specifies a subexpression in the regular expression, and the value of the function is the starting position of the match for that subexpression. The value is `nil' for a subexpression inside a `\|' alternative that wasn't used or a repetition that repeated zero times. - Function: match-end count This function is like `match-beginning' except that it returns the position of the end of the match, rather than the position of the beginning. Here is an example of using the match data, with a comment showing the positions within the text: (string-match "\\(qu\\)\\(ick\\)" "The quick fox jumped quickly.") ;0123456789 => 4 (match-string 0 "The quick fox jumped quickly.") => "quick" (match-string 1 "The quick fox jumped quickly.") => "qu" (match-string 2 "The quick fox jumped quickly.") => "ick" (match-beginning 1) ; The beginning of the match => 4 ; with `qu' is at index 4. (match-beginning 2) ; The beginning of the match => 6 ; with `ick' is at index 6. (match-end 1) ; The end of the match => 6 ; with `qu' is at index 6. (match-end 2) ; The end of the match => 9 ; with `ick' is at index 9. Here is another example. Point is initially located at the beginning of the line. Searching moves point to between the space and the word `in'. The beginning of the entire match is at the 9th character of the buffer (`T'), and the beginning of the match for the first subexpression is at the 13th character (`c'). (list (re-search-forward "The \\(cat \\)") (match-beginning 0) (match-beginning 1)) => (9 9 13) ---------- Buffer: foo ---------- I read "The cat -!-in the hat comes back" twice. ^ ^ 9 13 ---------- Buffer: foo ---------- (In this case, the index returned is a buffer position; the first character of the buffer counts as 1.)  File: elisp, Node: Entire Match Data, Next: Saving Match Data, Prev: Simple Match Data, Up: Match Data Accessing the Entire Match Data ------------------------------- The functions `match-data' and `set-match-data' read or write the entire match data, all at once. - Function: match-data This function returns a newly constructed list containing all the information on what text the last search matched. Element zero is the position of the beginning of the match for the whole expression; element one is the position of the end of the match for the expression. The next two elements are the positions of the beginning and end of the match for the first subexpression, and so on. In general, element number 2N corresponds to `(match-beginning N)'; and element number 2N + 1 corresponds to `(match-end N)'. All the elements are markers or `nil' if matching was done on a buffer, and all are integers or `nil' if matching was done on a string with `string-match'. As always, there must be no possibility of intervening searches between the call to a search function and the call to `match-data' that is intended to access the match data for that search. (match-data) => (# # # #) - Function: set-match-data match-list This function sets the match data from the elements of MATCH-LIST, which should be a list that was the value of a previous call to `match-data'. If MATCH-LIST refers to a buffer that doesn't exist, you don't get an error; that sets the match data in a meaningless but harmless way. `store-match-data' is a semi-obsolete alias for `set-match-data'.  File: elisp, Node: Saving Match Data, Prev: Entire Match Data, Up: Match Data Saving and Restoring the Match Data ----------------------------------- When you call a function that may do a search, you may need to save and restore the match data around that call, if you want to preserve the match data from an earlier search for later use. Here is an example that shows the problem that arises if you fail to save the match data: (re-search-forward "The \\(cat \\)") => 48 (foo) ; Perhaps `foo' does ; more searching. (match-end 0) => 61 ; Unexpected result--not 48! You can save and restore the match data with `save-match-data': - Macro: save-match-data body... This macro executes BODY, saving and restoring the match data around it. You could use `set-match-data' together with `match-data' to imitate the effect of the special form `save-match-data'. Here is how: (let ((data (match-data))) (unwind-protect ... ; Ok to change the original match data. (set-match-data data))) Emacs automatically saves and restores the match data when it runs process filter functions (*note Filter Functions::) and process sentinels (*note Sentinels::).  File: elisp, Node: Searching and Case, Next: Standard Regexps, Prev: Match Data, Up: Searching and Matching Searching and Case ================== By default, searches in Emacs ignore the case of the text they are searching through; if you specify searching for `FOO', then `Foo' or `foo' is also considered a match. This applies to regular expressions, too; thus, `[aB]' would match `a' or `A' or `b' or `B'. If you do not want this feature, set the variable `case-fold-search' to `nil'. Then all letters must match exactly, including case. This is a buffer-local variable; altering the variable affects only the current buffer. (*Note Intro to Buffer-Local::.) Alternatively, you may change the value of `default-case-fold-search', which is the default value of `case-fold-search' for buffers that do not override it. Note that the user-level incremental search feature handles case distinctions differently. When given a lower case letter, it looks for a match of either case, but when given an upper case letter, it looks for an upper case letter only. But this has nothing to do with the searching functions used in Lisp code. - User Option: case-replace This variable determines whether the replacement functions should preserve case. If the variable is `nil', that means to use the replacement text verbatim. A non-`nil' value means to convert the case of the replacement text according to the text being replaced. This variable is used by passing it as an argument to the function `replace-match'. *Note Replacing Match::. - User Option: case-fold-search This buffer-local variable determines whether searches should ignore case. If the variable is `nil' they do not ignore case; otherwise they do ignore case. - Variable: default-case-fold-search The value of this variable is the default value for `case-fold-search' in buffers that do not override it. This is the same as `(default-value 'case-fold-search)'.  File: elisp, Node: Standard Regexps, Prev: Searching and Case, Up: Searching and Matching Standard Regular Expressions Used in Editing ============================================ This section describes some variables that hold regular expressions used for certain purposes in editing: - Variable: page-delimiter This is the regular expression describing line-beginnings that separate pages. The default value is `"^\014"' (i.e., `"^^L"' or `"^\C-l"'); this matches a line that starts with a formfeed character. The following two regular expressions should _not_ assume the match always starts at the beginning of a line; they should not use `^' to anchor the match. Most often, the paragraph commands do check for a match only at the beginning of a line, which means that `^' would be superfluous. When there is a nonzero left margin, they accept matches that start after the left margin. In that case, a `^' would be incorrect. However, a `^' is harmless in modes where a left margin is never used. - Variable: paragraph-separate This is the regular expression for recognizing the beginning of a line that separates paragraphs. (If you change this, you may have to change `paragraph-start' also.) The default value is `"[ \t\f]*$"', which matches a line that consists entirely of spaces, tabs, and form feeds (after its left margin). - Variable: paragraph-start This is the regular expression for recognizing the beginning of a line that starts _or_ separates paragraphs. The default value is `"[ \t\n\f]"', which matches a line starting with a space, tab, newline, or form feed (after its left margin). - Variable: sentence-end This is the regular expression describing the end of a sentence. (All paragraph boundaries also end sentences, regardless.) The default value is: "[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*" This means a period, question mark or exclamation mark, followed optionally by a closing parenthetical character, followed by tabs, spaces or new lines. For a detailed explanation of this regular expression, see *Note Regexp Example::.