This is Info file ../../info/lispref.info, produced by Makeinfo-1.63 from the input file lispref.texi. Edition History: GNU Emacs Lisp Reference Manual Second Edition (v2.01), May 1993 GNU Emacs Lisp Reference Manual Further Revised (v2.02), August 1993 Lucid Emacs Lisp Reference Manual (for 19.10) First Edition, March 1994 XEmacs Lisp Programmer's Manual (for 19.12) Second Edition, April 1995 GNU Emacs Lisp Reference Manual v2.4, June 1995 XEmacs Lisp Programmer's Manual (for 19.13) Third Edition, July 1995 Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software Foundation, Inc. Copyright (C) 1994, 1995 Sun Microsystems, Inc. Copyright (C) 1995 Amdahl Corporation. Copyright (C) 1995 Ben Wing. 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: lispref.info, Node: Searching and Matching, Next: Syntax Tables, Prev: Text, Up: Top Searching and Matching ********************** XEmacs provides two ways to search through a buffer for specified text: exact string searches and regular expression searches. After a regular expression search, you can examine the "match data" to determine which text matched the whole regular expression or various portions of it. * Menu: * String Search:: Search for an exact match. * Regular Expressions:: Describing classes of strings. * Regexp Search:: Searching for a match for a regexp. * POSIX Regexps:: Searching POSIX-style for the longest match. * Search and Replace:: Internals of `query-replace'. * Match Data:: Finding out which part of the text matched various parts of a regexp, after regexp search. * Searching and Case:: Case-independent or case-significant searching. * Standard Regexps:: Useful regexps for finding sentences, pages,... The `skip-chars...' functions also perform a kind of searching. *Note Skipping Characters::.  File: lispref.info, Node: String Search, Next: Regular Expressions, Up: Searching and Matching Searching for Strings ===================== These are the primitive functions for searching through the text in a buffer. They are meant for use in programs, but you may call them interactively. If you do so, they prompt for the search string; LIMIT and NOERROR are set to `nil', and REPEAT is set to 1. - Command: search-forward STRING &optional LIMIT NOERROR REPEAT This function searches forward from point for an exact match for STRING. If successful, it sets point to the end of the occurrence found, and returns the new value of point. If no match is found, the value and side effects depend on NOERROR (see below). In the following example, point is initially at the beginning of the line. Then `(search-forward "fox")' moves point after the last letter of `fox': ---------- Buffer: foo ---------- -!-The quick brown fox jumped over the lazy dog. ---------- Buffer: foo ---------- (search-forward "fox") => 20 ---------- Buffer: foo ---------- The quick brown fox-!- jumped over the lazy dog. ---------- Buffer: foo ---------- The argument LIMIT specifies the upper bound to the search. (It must be a position in the current buffer.) No match extending after that position is accepted. If LIMIT is omitted or `nil', it defaults to the end of the accessible portion of the buffer. What happens when the search fails depends on the value of NOERROR. If NOERROR is `nil', a `search-failed' error is signaled. If NOERROR is `t', `search-forward' returns `nil' and does nothing. If NOERROR is neither `nil' nor `t', then `search-forward' moves point to the upper bound and returns `nil'. (It would be more consistent now to return the new position of point in that case, but some programs may depend on a value of `nil'.) 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 these successive searches succeed, the function succeeds, moving point and returning its new value. Otherwise the search fails. - Command: search-backward STRING &optional LIMIT NOERROR REPEAT This function searches backward from point for STRING. It is just like `search-forward' except that it searches backwards and leaves point at the beginning of the match. - Command: word-search-forward STRING &optional LIMIT NOERROR REPEAT This function searches forward from point for a "word" match for STRING. If it finds a match, it sets point to the end of the match found, and returns the new value of point. Word matching regards STRING as a sequence of words, disregarding punctuation that separates them. It searches the buffer for the same sequence of words. Each word must be distinct in the buffer (searching for the word `ball' does not match the word `balls'), but the details of punctuation and spacing are ignored (searching for `ball boy' does match `ball. Boy!'). In this example, point is initially at the beginning of the buffer; the search leaves it between the `y' and the `!'. ---------- Buffer: foo ---------- -!-He said "Please! Find the ball boy!" ---------- Buffer: foo ---------- (word-search-forward "Please find the ball, boy.") => 35 ---------- Buffer: foo ---------- He said "Please! Find the ball boy-!-!" ---------- Buffer: foo ---------- If LIMIT is non-`nil' (it must be a position in the current buffer), then it is the upper bound to the search. The match found must not extend after that position. If NOERROR is `nil', then `word-search-forward' signals an error if the search fails. If NOERROR is `t', then it returns `nil' instead of signaling an error. If NOERROR is neither `nil' nor `t', it moves point to LIMIT (or the end of the buffer) and returns `nil'. If REPEAT is non-`nil', then the search is repeated that many times. Point is positioned at the end of the last match. - Command: word-search-backward STRING &optional LIMIT NOERROR REPEAT This function searches backward from point for a word match to STRING. This function is just like `word-search-forward' except that it searches backward and normally leaves point at the beginning of the match.  File: lispref.info, Node: Regular Expressions, Next: Regexp Search, Prev: String Search, Up: Searching and Matching Regular Expressions =================== A "regular expression" ("regexp", for short) is a pattern that denotes a (possibly infinite) set of strings. Searching for matches for a regexp is a very powerful operation. This section explains how to write regexps; the following section says how to search for them. * Menu: * Syntax of Regexps:: Rules for writing regular expressions. * Regexp Example:: Illustrates regular expression syntax.  File: lispref.info, Node: Syntax of Regexps, Next: Regexp Example, Up: Regular Expressions Syntax of Regular Expressions ----------------------------- Regular expressions have a syntax in which a few characters are special constructs and the rest are "ordinary". An ordinary character is a simple regular expression that matches that character and nothing else. The special characters are `.', `*', `+', `?', `[', `]', `^', `$', and `\'; no new special characters will be defined in the future. Any other character appearing in a regular expression is ordinary, unless a `\' precedes it. For example, `f' is not a special character, so it is ordinary, and therefore `f' is a regular expression that matches the string `f' and no other string. (It does *not* match the string `ff'.) Likewise, `o' is a regular expression that matches only `o'. Any two regular expressions A and B can be concatenated. The result is a regular expression that matches a string if A matches some amount of the beginning of that string and B matches the rest of the string. As a simple example, we can concatenate the regular expressions `f' and `o' to get the regular expression `fo', which matches only the string `fo'. Still trivial. To do something more powerful, you need to use one of the special characters. Here is a list of them: `. (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 suffix operator that means to repeat the preceding regular expression as many times as possible. In `fo*', the `*' applies to the `o', so `fo*' matches one `f' followed by any number of `o's. The case of zero `o's is allowed: `fo*' does match `f'. `*' always applies to the *smallest* possible preceding expression. Thus, `fo*' has a repeating `o', not a repeating `fo'. 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 case that makes 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 match the sequence `xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz'. 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 suffix operator similar to `*' except that the preceding expression must match 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 suffix operator similar to `*' except that the preceding expression can match either once or not at all. For example, `ca?r' matches `car' or `cr', but does not match anyhing else. `[ ... ]' `[' begins a "character set", which is terminated by a `]'. In the simplest case, the characters between the two brackets form the set. 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. The usual regular expression special characters are not special inside a character set. A completely different set of special characters exists inside character sets: `]', `-' and `^'. `-' is used for ranges of characters. To write a range, write two characters with a `-' between them. Thus, `[a-z]' matches any lower case letter. Ranges may be intermixed freely with individual characters, as in `[a-z$%.]', which matches any lower case letter or `$', `%', or a period. To include a `]' in a character set, make it the first character. For example, `[]a]' matches `]' or `a'. To include a `-', write `-' as the first character in the set, or put it immediately after a range. (You can replace one individual character C with the range `C-C' to make a place to put the `-'.) There is no way to write a set containing just `-' and `]'. To include `^' in a set, put it anywhere but at the beginning of the set. `[^ ... ]' `[^' begins a "complement character set", 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 set unless it is the first character. The character following the `^' is treated as if it were first (thus, `-' and `]' are not special there). Note that a complement character set can match a newline, unless newline is mentioned as one of the characters not to match. `^' 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 `\n'. `$' is similar to `^' but matches only at the end of a line. Thus, `x+$' matches a string of one `x' or more at the end of a line. When matching a string instead of a buffer, `$' matches at the end of the string or before a newline character `\n'. `\' has two functions: it quotes the special characters (including `\'), and it introduces additional special constructs. Because `\' quotes special characters, `\$' is a regular expression that matches only `$', 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. For the most part, `\' followed by any character matches only that character. However, there are several exceptions: characters that, when preceded by `\', are special constructs. Such characters are always ordinary when encountered on their own. Here is a table of `\' 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 `\|'. `\( ... \)' is a grouping construct that serves three purposes: 1. To enclose a set of `\|' alternatives for other operations. Thus, `\(foo\|bar\)x' matches either `foox' or `barx'. 2. To enclose an expression for a suffix operator such as `*' to act on. Thus, `ba\(na\)*' matches `bananana', etc., with any (zero or more) number of `na' strings. 3. To record a matched substring for future reference. This last application is not a consequence of the idea of a parenthetical grouping; it is a separate feature that happens to be assigned as a second meaning to the same `\( ... \)' construct because there is no conflict in practice between the two meanings. Here is an explanation of this feature: `\DIGIT' matches the same text that matched the DIGITth occurrence of a `\( ... \)' construct. In other words, after the end of a `\( ... \)' construct. the matcher remembers the beginning and end of the text matched by that construct. Then, 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 `\( ... \)' constructs appearing in a regular expression 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 `\( ... \)' 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. `\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. *Note Syntax Tables::, for a list of syntax codes and the characters that stand for them. `\SCODE' matches any character whose syntax is not CODE. 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 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 the empty string, but only at the end of a word. 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. - Function: regexp-quote STRING This function returns a regular expression string that matches exactly STRING and nothing else. This allows you to request an exact string match 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-"))  File: lispref.info, Node: Regexp Example, Prev: Syntax of Regexps, Up: Regular Expressions Complex Regexp Example ---------------------- Here is a complicated regexp, used by XEmacs 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. "[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*" In contrast, if you evaluate the variable `sentence-end', you will see the following: sentence-end => "[.?!][]\"')}]*\\($\\| $\\| \\| \\)[ ]*" In this output, tab and newline appear as themselves. This regular expression contains four parts in succession and can be deciphered as follows: `[.?!]' The first part of the pattern is a character set that matches any one of three characters: period, question mark, and exclamation mark. The match must begin with one of these three characters. `[]\"')}]*' The second part of the pattern matches any closing braces and quotation marks, zero or more of them, that may follow the period, question mark or exclamation mark. The `\"' is Lisp syntax for a double-quote in a string. The `*' at the end indicates that the immediately preceding regular expression (a character set, in this case) may be repeated zero or more times. `\\($\\| $\\|\t\\| \\)' The third part of the pattern matches the whitespace that follows the end of a sentence: the end of a line, 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: lispref.info, Node: Regexp Search, Next: POSIX Regexps, Prev: Regular Expressions, Up: Searching and Matching Regular Expression Searching ============================ In XEmacs, you can search for the next match for a regexp either incrementally or not. Incremental search commands are described in the `The XEmacs Reference Manual'. *Note Regular Expression Search: (emacs)Regexp Search. Here we describe only the search functions useful in programs. The principal one is `re-search-forward'. - 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. What happens when the search 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'. 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 these successive searches succeed, the function succeeds, moving point and returning its new value. Otherwise the search fails. 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 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 regexps 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: lispref.info, 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. In Emacs versions prior to 19.29, these functions did not exist, and the functions described above implemented full POSIX backtracking. - 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: lispref.info, Node: Search and Replace, Next: Match Data, Prev: POSIX Regexps, Up: Searching and Matching Search and Replace ================== - Function: perform-replace FROM-STRING REPLACEMENTS 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 and replaces some or all of them. 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 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. 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: lispref.info, Node: Match Data, Next: Searching and Case, Prev: Search and Replace, Up: Searching and Matching The Match Data ============== XEmacs keeps track of the positions of the start and end of 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: * Simple Match Data:: Accessing single items of match data, such as where a particular subexpression started. * Replacing Match:: Replacing a substring that was matched. * Entire Match Data:: Accessing the entire match data at once, as a list. * Saving Match Data:: Saving and restoring the match data.  File: lispref.info, Node: Simple Match Data, Next: 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. - 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 COUNT is out of range, or if that subexpression didn't match anything, the value is `nil'. 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. Otherwise, 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. - 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 expresion, 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 in the match. - 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: lispref.info, Node: Replacing Match, Next: Entire Match Data, Prev: 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 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 `case-replace' is `nil', then case conversion is not done, regardless of the value of FIXED-CASE. *Note Searching and 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.  File: lispref.info, Node: Entire Match Data, Next: Saving Match Data, Prev: Replacing Match, 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'. (In Emacs 18 and earlier versions, markers were used even for matching on a string, except in the case of the integer 0.) 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 an alias for `set-match-data'.  File: lispref.info, 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 special form executes BODY, saving and restoring the match data around it. You can use `set-match-data' together with `match-data' to imitate the effect of the special form `save-match-data'. This is useful for writing code that can run in Emacs 18. Here is how: (let ((data (match-data))) (unwind-protect ... ; May 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: lispref.info, 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. Regexps, and in particular character sets, are included: 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 Lisp functions use. - 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. The function `replace-match' is where this variable actually has its effect. *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: lispref.info, 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 regexp 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::.  File: lispref.info, Node: Syntax Tables, Next: Abbrevs, Prev: Searching and Matching, Up: Top Syntax Tables ************* A "syntax table" specifies the syntactic textual function of each character. This information is used by the parsing commands, the complex movement commands, and others to determine where words, symbols, and other syntactic constructs begin and end. The current syntax table controls the meaning of the word motion functions (*note Word Motion::.) and the list motion functions (*note List Motion::.) as well as the functions in this chapter. * Menu: * Basics: Syntax Basics. Basic concepts of syntax tables. * Desc: Syntax Descriptors. How characters are classified. * Syntax Table Functions:: How to create, examine and alter syntax tables. * Motion and Syntax:: Moving over characters with certain syntaxes. * Parsing Expressions:: Parsing balanced expressions using the syntax table. * Standard Syntax Tables:: Syntax tables used by various major modes. * Syntax Table Internals:: How syntax table information is stored.