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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. | |
4 | @c See the file elisp.texi for copying conditions. | |
5 | @setfilename ../info/searching | |
6 | @node Searching and Matching, Syntax Tables, Text, Top | |
7 | @chapter Searching and Matching | |
8 | @cindex searching | |
9 | ||
10 | GNU Emacs provides two ways to search through a buffer for specified | |
11 | text: exact string searches and regular expression searches. After a | |
12 | regular expression search, you can examine the @dfn{match data} to | |
13 | determine which text matched the whole regular expression or various | |
14 | portions of it. | |
15 | ||
16 | @menu | |
17 | * String Search:: Search for an exact match. | |
18 | * Regular Expressions:: Describing classes of strings. | |
19 | * Regexp Search:: Searching for a match for a regexp. | |
22697dac | 20 | * POSIX Regexps:: Searching POSIX-style for the longest match. |
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21 | * Search and Replace:: Internals of @code{query-replace}. |
22 | * Match Data:: Finding out which part of the text matched | |
23 | various parts of a regexp, after regexp search. | |
24 | * Searching and Case:: Case-independent or case-significant searching. | |
25 | * Standard Regexps:: Useful regexps for finding sentences, pages,... | |
26 | @end menu | |
27 | ||
28 | The @samp{skip-chars@dots{}} functions also perform a kind of searching. | |
29 | @xref{Skipping Characters}. | |
30 | ||
31 | @node String Search | |
32 | @section Searching for Strings | |
33 | @cindex string search | |
34 | ||
35 | These are the primitive functions for searching through the text in a | |
36 | buffer. They are meant for use in programs, but you may call them | |
37 | interactively. If you do so, they prompt for the search string; | |
38 | @var{limit} and @var{noerror} are set to @code{nil}, and @var{repeat} | |
39 | is set to 1. | |
40 | ||
41 | @deffn Command search-forward string &optional limit noerror repeat | |
42 | This function searches forward from point for an exact match for | |
43 | @var{string}. If successful, it sets point to the end of the occurrence | |
44 | found, and returns the new value of point. If no match is found, the | |
45 | value and side effects depend on @var{noerror} (see below). | |
46 | @c Emacs 19 feature | |
47 | ||
48 | In the following example, point is initially at the beginning of the | |
49 | line. Then @code{(search-forward "fox")} moves point after the last | |
50 | letter of @samp{fox}: | |
51 | ||
52 | @example | |
53 | @group | |
54 | ---------- Buffer: foo ---------- | |
55 | @point{}The quick brown fox jumped over the lazy dog. | |
56 | ---------- Buffer: foo ---------- | |
57 | @end group | |
58 | ||
59 | @group | |
60 | (search-forward "fox") | |
61 | @result{} 20 | |
62 | ||
63 | ---------- Buffer: foo ---------- | |
64 | The quick brown fox@point{} jumped over the lazy dog. | |
65 | ---------- Buffer: foo ---------- | |
66 | @end group | |
67 | @end example | |
68 | ||
69 | The argument @var{limit} specifies the upper bound to the search. (It | |
70 | must be a position in the current buffer.) No match extending after | |
71 | that position is accepted. If @var{limit} is omitted or @code{nil}, it | |
72 | defaults to the end of the accessible portion of the buffer. | |
73 | ||
74 | @kindex search-failed | |
75 | What happens when the search fails depends on the value of | |
76 | @var{noerror}. If @var{noerror} is @code{nil}, a @code{search-failed} | |
77 | error is signaled. If @var{noerror} is @code{t}, @code{search-forward} | |
78 | returns @code{nil} and does nothing. If @var{noerror} is neither | |
79 | @code{nil} nor @code{t}, then @code{search-forward} moves point to the | |
80 | upper bound and returns @code{nil}. (It would be more consistent now | |
81 | to return the new position of point in that case, but some programs | |
82 | may depend on a value of @code{nil}.) | |
83 | ||
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84 | If @var{repeat} is supplied (it must be a positive number), then the |
85 | search is repeated that many times (each time starting at the end of the | |
86 | previous time's match). If these successive searches succeed, the | |
87 | function succeeds, moving point and returning its new value. Otherwise | |
88 | the search fails. | |
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89 | @end deffn |
90 | ||
91 | @deffn Command search-backward string &optional limit noerror repeat | |
92 | This function searches backward from point for @var{string}. It is | |
93 | just like @code{search-forward} except that it searches backwards and | |
94 | leaves point at the beginning of the match. | |
95 | @end deffn | |
96 | ||
97 | @deffn Command word-search-forward string &optional limit noerror repeat | |
98 | @cindex word search | |
99 | This function searches forward from point for a ``word'' match for | |
100 | @var{string}. If it finds a match, it sets point to the end of the | |
101 | match found, and returns the new value of point. | |
102 | @c Emacs 19 feature | |
103 | ||
104 | Word matching regards @var{string} as a sequence of words, disregarding | |
105 | punctuation that separates them. It searches the buffer for the same | |
106 | sequence of words. Each word must be distinct in the buffer (searching | |
107 | for the word @samp{ball} does not match the word @samp{balls}), but the | |
108 | details of punctuation and spacing are ignored (searching for @samp{ball | |
109 | boy} does match @samp{ball. Boy!}). | |
110 | ||
111 | In this example, point is initially at the beginning of the buffer; the | |
112 | search leaves it between the @samp{y} and the @samp{!}. | |
113 | ||
114 | @example | |
115 | @group | |
116 | ---------- Buffer: foo ---------- | |
117 | @point{}He said "Please! Find | |
118 | the ball boy!" | |
119 | ---------- Buffer: foo ---------- | |
120 | @end group | |
121 | ||
122 | @group | |
123 | (word-search-forward "Please find the ball, boy.") | |
124 | @result{} 35 | |
125 | ||
126 | ---------- Buffer: foo ---------- | |
127 | He said "Please! Find | |
128 | the ball boy@point{}!" | |
129 | ---------- Buffer: foo ---------- | |
130 | @end group | |
131 | @end example | |
132 | ||
133 | If @var{limit} is non-@code{nil} (it must be a position in the current | |
134 | buffer), then it is the upper bound to the search. The match found must | |
135 | not extend after that position. | |
136 | ||
137 | If @var{noerror} is @code{nil}, then @code{word-search-forward} signals | |
138 | an error if the search fails. If @var{noerror} is @code{t}, then it | |
139 | returns @code{nil} instead of signaling an error. If @var{noerror} is | |
140 | neither @code{nil} nor @code{t}, it moves point to @var{limit} (or the | |
141 | end of the buffer) and returns @code{nil}. | |
142 | ||
143 | If @var{repeat} is non-@code{nil}, then the search is repeated that many | |
144 | times. Point is positioned at the end of the last match. | |
145 | @end deffn | |
146 | ||
147 | @deffn Command word-search-backward string &optional limit noerror repeat | |
148 | This function searches backward from point for a word match to | |
149 | @var{string}. This function is just like @code{word-search-forward} | |
150 | except that it searches backward and normally leaves point at the | |
151 | beginning of the match. | |
152 | @end deffn | |
153 | ||
154 | @node Regular Expressions | |
155 | @section Regular Expressions | |
156 | @cindex regular expression | |
157 | @cindex regexp | |
158 | ||
159 | A @dfn{regular expression} (@dfn{regexp}, for short) is a pattern that | |
160 | denotes a (possibly infinite) set of strings. Searching for matches for | |
161 | a regexp is a very powerful operation. This section explains how to write | |
162 | regexps; the following section says how to search for them. | |
163 | ||
164 | @menu | |
165 | * Syntax of Regexps:: Rules for writing regular expressions. | |
166 | * Regexp Example:: Illustrates regular expression syntax. | |
167 | @end menu | |
168 | ||
169 | @node Syntax of Regexps | |
170 | @subsection Syntax of Regular Expressions | |
171 | ||
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172 | Regular expressions have a syntax in which a few characters are |
173 | special constructs and the rest are @dfn{ordinary}. An ordinary | |
174 | character is a simple regular expression that matches that character and | |
175 | nothing else. The special characters are @samp{.}, @samp{*}, @samp{+}, | |
176 | @samp{?}, @samp{[}, @samp{]}, @samp{^}, @samp{$}, and @samp{\}; no new | |
177 | special characters will be defined in the future. Any other character | |
178 | appearing in a regular expression is ordinary, unless a @samp{\} | |
179 | precedes it. | |
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180 | |
181 | For example, @samp{f} is not a special character, so it is ordinary, and | |
182 | therefore @samp{f} is a regular expression that matches the string | |
183 | @samp{f} and no other string. (It does @emph{not} match the string | |
184 | @samp{ff}.) Likewise, @samp{o} is a regular expression that matches | |
185 | only @samp{o}.@refill | |
186 | ||
187 | Any two regular expressions @var{a} and @var{b} can be concatenated. The | |
61cfa852 | 188 | result is a regular expression that matches a string if @var{a} matches |
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189 | some amount of the beginning of that string and @var{b} matches the rest of |
190 | the string.@refill | |
191 | ||
192 | As a simple example, we can concatenate the regular expressions @samp{f} | |
193 | and @samp{o} to get the regular expression @samp{fo}, which matches only | |
194 | the string @samp{fo}. Still trivial. To do something more powerful, you | |
195 | need to use one of the special characters. Here is a list of them: | |
196 | ||
197 | @need 1200 | |
198 | @table @kbd | |
199 | @item .@: @r{(Period)} | |
200 | @cindex @samp{.} in regexp | |
201 | is a special character that matches any single character except a newline. | |
202 | Using concatenation, we can make regular expressions like @samp{a.b}, which | |
203 | matches any three-character string that begins with @samp{a} and ends with | |
204 | @samp{b}.@refill | |
205 | ||
206 | @item * | |
207 | @cindex @samp{*} in regexp | |
208 | is not a construct by itself; it is a suffix operator that means to | |
209 | repeat the preceding regular expression as many times as possible. In | |
210 | @samp{fo*}, the @samp{*} applies to the @samp{o}, so @samp{fo*} matches | |
211 | one @samp{f} followed by any number of @samp{o}s. The case of zero | |
212 | @samp{o}s is allowed: @samp{fo*} does match @samp{f}.@refill | |
213 | ||
214 | @samp{*} always applies to the @emph{smallest} possible preceding | |
215 | expression. Thus, @samp{fo*} has a repeating @samp{o}, not a | |
216 | repeating @samp{fo}.@refill | |
217 | ||
218 | The matcher processes a @samp{*} construct by matching, immediately, | |
219 | as many repetitions as can be found. Then it continues with the rest | |
220 | of the pattern. If that fails, backtracking occurs, discarding some | |
221 | of the matches of the @samp{*}-modified construct in case that makes | |
222 | it possible to match the rest of the pattern. For example, in matching | |
223 | @samp{ca*ar} against the string @samp{caaar}, the @samp{a*} first | |
224 | tries to match all three @samp{a}s; but the rest of the pattern is | |
225 | @samp{ar} and there is only @samp{r} left to match, so this try fails. | |
226 | The next alternative is for @samp{a*} to match only two @samp{a}s. | |
227 | With this choice, the rest of the regexp matches successfully.@refill | |
228 | ||
73031603 | 229 | Nested repetition operators can be extremely slow if they specify |
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230 | backtracking loops. For example, it could take hours for the regular |
231 | expression @samp{\(x+y*\)*a} to match the sequence | |
232 | @samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz}. The slowness is because | |
233 | Emacs must try each imaginable way of grouping the 35 @samp{x}'s before | |
234 | concluding that none of them can work. To make sure your regular | |
235 | expressions run fast, check nested repetitions carefully. | |
73031603 | 236 | |
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237 | @item + |
238 | @cindex @samp{+} in regexp | |
239 | is a suffix operator similar to @samp{*} except that the preceding | |
240 | expression must match at least once. So, for example, @samp{ca+r} | |
241 | matches the strings @samp{car} and @samp{caaaar} but not the string | |
242 | @samp{cr}, whereas @samp{ca*r} matches all three strings. | |
243 | ||
244 | @item ? | |
245 | @cindex @samp{?} in regexp | |
246 | is a suffix operator similar to @samp{*} except that the preceding | |
247 | expression can match either once or not at all. For example, | |
248 | @samp{ca?r} matches @samp{car} or @samp{cr}, but does not match anyhing | |
249 | else. | |
250 | ||
251 | @item [ @dots{} ] | |
252 | @cindex character set (in regexp) | |
253 | @cindex @samp{[} in regexp | |
254 | @cindex @samp{]} in regexp | |
255 | @samp{[} begins a @dfn{character set}, which is terminated by a | |
256 | @samp{]}. In the simplest case, the characters between the two brackets | |
257 | form the set. Thus, @samp{[ad]} matches either one @samp{a} or one | |
258 | @samp{d}, and @samp{[ad]*} matches any string composed of just @samp{a}s | |
259 | and @samp{d}s (including the empty string), from which it follows that | |
260 | @samp{c[ad]*r} matches @samp{cr}, @samp{car}, @samp{cdr}, | |
261 | @samp{caddaar}, etc.@refill | |
262 | ||
263 | The usual regular expression special characters are not special inside a | |
264 | character set. A completely different set of special characters exists | |
265 | inside character sets: @samp{]}, @samp{-} and @samp{^}.@refill | |
266 | ||
267 | @samp{-} is used for ranges of characters. To write a range, write two | |
268 | characters with a @samp{-} between them. Thus, @samp{[a-z]} matches any | |
269 | lower case letter. Ranges may be intermixed freely with individual | |
270 | characters, as in @samp{[a-z$%.]}, which matches any lower case letter | |
61cfa852 | 271 | or @samp{$}, @samp{%}, or a period.@refill |
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272 | |
273 | To include a @samp{]} in a character set, make it the first character. | |
274 | For example, @samp{[]a]} matches @samp{]} or @samp{a}. To include a | |
61cfa852 | 275 | @samp{-}, write @samp{-} as the first character in the set, or put it |
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276 | immediately after a range. (You can replace one individual character |
277 | @var{c} with the range @samp{@var{c}-@var{c}} to make a place to put the | |
61cfa852 | 278 | @samp{-}.) There is no way to write a set containing just @samp{-} and |
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279 | @samp{]}. |
280 | ||
281 | To include @samp{^} in a set, put it anywhere but at the beginning of | |
282 | the set. | |
283 | ||
284 | @item [^ @dots{} ] | |
285 | @cindex @samp{^} in regexp | |
286 | @samp{[^} begins a @dfn{complement character set}, which matches any | |
287 | character except the ones specified. Thus, @samp{[^a-z0-9A-Z]} | |
288 | matches all characters @emph{except} letters and digits.@refill | |
289 | ||
290 | @samp{^} is not special in a character set unless it is the first | |
291 | character. The character following the @samp{^} is treated as if it | |
292 | were first (thus, @samp{-} and @samp{]} are not special there). | |
293 | ||
294 | Note that a complement character set can match a newline, unless | |
295 | newline is mentioned as one of the characters not to match. | |
296 | ||
297 | @item ^ | |
298 | @cindex @samp{^} in regexp | |
299 | @cindex beginning of line in regexp | |
61cfa852 RS |
300 | is a special character that matches the empty string, but only at the |
301 | beginning of a line in the text being matched. Otherwise it fails to | |
302 | match anything. Thus, @samp{^foo} matches a @samp{foo} that occurs at | |
303 | the beginning of a line. | |
7015aca4 | 304 | |
61cfa852 RS |
305 | When matching a string instead of a buffer, @samp{^} matches at the |
306 | beginning of the string or after a newline character @samp{\n}. | |
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307 | |
308 | @item $ | |
309 | @cindex @samp{$} in regexp | |
310 | is similar to @samp{^} but matches only at the end of a line. Thus, | |
311 | @samp{x+$} matches a string of one @samp{x} or more at the end of a line. | |
312 | ||
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313 | When matching a string instead of a buffer, @samp{$} matches at the end |
314 | of the string or before a newline character @samp{\n}. | |
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315 | |
316 | @item \ | |
317 | @cindex @samp{\} in regexp | |
318 | has two functions: it quotes the special characters (including | |
319 | @samp{\}), and it introduces additional special constructs. | |
320 | ||
321 | Because @samp{\} quotes special characters, @samp{\$} is a regular | |
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322 | expression that matches only @samp{$}, and @samp{\[} is a regular |
323 | expression that matches only @samp{[}, and so on. | |
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324 | |
325 | Note that @samp{\} also has special meaning in the read syntax of Lisp | |
326 | strings (@pxref{String Type}), and must be quoted with @samp{\}. For | |
327 | example, the regular expression that matches the @samp{\} character is | |
328 | @samp{\\}. To write a Lisp string that contains the characters | |
329 | @samp{\\}, Lisp syntax requires you to quote each @samp{\} with another | |
330 | @samp{\}. Therefore, the read syntax for a regular expression matching | |
331 | @samp{\} is @code{"\\\\"}.@refill | |
332 | @end table | |
333 | ||
b22f3a19 | 334 | @strong{Please note:} For historical compatibility, special characters |
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335 | are treated as ordinary ones if they are in contexts where their special |
336 | meanings make no sense. For example, @samp{*foo} treats @samp{*} as | |
337 | ordinary since there is no preceding expression on which the @samp{*} | |
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338 | can act. It is poor practice to depend on this behavior; quote the |
339 | special character anyway, regardless of where it appears.@refill | |
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340 | |
341 | For the most part, @samp{\} followed by any character matches only | |
342 | that character. However, there are several exceptions: characters | |
61cfa852 | 343 | that, when preceded by @samp{\}, are special constructs. Such |
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344 | characters are always ordinary when encountered on their own. Here |
345 | is a table of @samp{\} constructs: | |
346 | ||
347 | @table @kbd | |
348 | @item \| | |
349 | @cindex @samp{|} in regexp | |
350 | @cindex regexp alternative | |
351 | specifies an alternative. | |
352 | Two regular expressions @var{a} and @var{b} with @samp{\|} in | |
353 | between form an expression that matches anything that either @var{a} or | |
354 | @var{b} matches.@refill | |
355 | ||
356 | Thus, @samp{foo\|bar} matches either @samp{foo} or @samp{bar} | |
357 | but no other string.@refill | |
358 | ||
359 | @samp{\|} applies to the largest possible surrounding expressions. Only a | |
360 | surrounding @samp{\( @dots{} \)} grouping can limit the grouping power of | |
361 | @samp{\|}.@refill | |
362 | ||
363 | Full backtracking capability exists to handle multiple uses of @samp{\|}. | |
364 | ||
365 | @item \( @dots{} \) | |
366 | @cindex @samp{(} in regexp | |
367 | @cindex @samp{)} in regexp | |
368 | @cindex regexp grouping | |
369 | is a grouping construct that serves three purposes: | |
370 | ||
371 | @enumerate | |
372 | @item | |
373 | To enclose a set of @samp{\|} alternatives for other operations. | |
374 | Thus, @samp{\(foo\|bar\)x} matches either @samp{foox} or @samp{barx}. | |
375 | ||
376 | @item | |
377 | To enclose an expression for a suffix operator such as @samp{*} to act | |
378 | on. Thus, @samp{ba\(na\)*} matches @samp{bananana}, etc., with any | |
379 | (zero or more) number of @samp{na} strings.@refill | |
380 | ||
381 | @item | |
382 | To record a matched substring for future reference. | |
383 | @end enumerate | |
384 | ||
385 | This last application is not a consequence of the idea of a | |
61cfa852 | 386 | parenthetical grouping; it is a separate feature that happens to be |
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387 | assigned as a second meaning to the same @samp{\( @dots{} \)} construct |
388 | because there is no conflict in practice between the two meanings. | |
389 | Here is an explanation of this feature: | |
390 | ||
391 | @item \@var{digit} | |
61cfa852 | 392 | matches the same text that matched the @var{digit}th occurrence of a |
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393 | @samp{\( @dots{} \)} construct. |
394 | ||
395 | In other words, after the end of a @samp{\( @dots{} \)} construct. the | |
396 | matcher remembers the beginning and end of the text matched by that | |
397 | construct. Then, later on in the regular expression, you can use | |
398 | @samp{\} followed by @var{digit} to match that same text, whatever it | |
399 | may have been. | |
400 | ||
401 | The strings matching the first nine @samp{\( @dots{} \)} constructs | |
402 | appearing in a regular expression are assigned numbers 1 through 9 in | |
403 | the order that the open parentheses appear in the regular expression. | |
404 | So you can use @samp{\1} through @samp{\9} to refer to the text matched | |
405 | by the corresponding @samp{\( @dots{} \)} constructs. | |
406 | ||
407 | For example, @samp{\(.*\)\1} matches any newline-free string that is | |
408 | composed of two identical halves. The @samp{\(.*\)} matches the first | |
409 | half, which may be anything, but the @samp{\1} that follows must match | |
410 | the same exact text. | |
411 | ||
412 | @item \w | |
413 | @cindex @samp{\w} in regexp | |
414 | matches any word-constituent character. The editor syntax table | |
415 | determines which characters these are. @xref{Syntax Tables}. | |
416 | ||
417 | @item \W | |
418 | @cindex @samp{\W} in regexp | |
61cfa852 | 419 | matches any character that is not a word constituent. |
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420 | |
421 | @item \s@var{code} | |
422 | @cindex @samp{\s} in regexp | |
423 | matches any character whose syntax is @var{code}. Here @var{code} is a | |
61cfa852 | 424 | character that represents a syntax code: thus, @samp{w} for word |
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425 | constituent, @samp{-} for whitespace, @samp{(} for open parenthesis, |
426 | etc. @xref{Syntax Tables}, for a list of syntax codes and the | |
427 | characters that stand for them. | |
428 | ||
429 | @item \S@var{code} | |
430 | @cindex @samp{\S} in regexp | |
431 | matches any character whose syntax is not @var{code}. | |
432 | @end table | |
433 | ||
61cfa852 | 434 | The following regular expression constructs match the empty string---that is, |
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435 | they don't use up any characters---but whether they match depends on the |
436 | context. | |
437 | ||
438 | @table @kbd | |
439 | @item \` | |
440 | @cindex @samp{\`} in regexp | |
441 | matches the empty string, but only at the beginning | |
442 | of the buffer or string being matched against. | |
443 | ||
444 | @item \' | |
445 | @cindex @samp{\'} in regexp | |
446 | matches the empty string, but only at the end of | |
447 | the buffer or string being matched against. | |
448 | ||
449 | @item \= | |
450 | @cindex @samp{\=} in regexp | |
451 | matches the empty string, but only at point. | |
452 | (This construct is not defined when matching against a string.) | |
453 | ||
454 | @item \b | |
455 | @cindex @samp{\b} in regexp | |
456 | matches the empty string, but only at the beginning or | |
457 | end of a word. Thus, @samp{\bfoo\b} matches any occurrence of | |
458 | @samp{foo} as a separate word. @samp{\bballs?\b} matches | |
459 | @samp{ball} or @samp{balls} as a separate word.@refill | |
460 | ||
461 | @item \B | |
462 | @cindex @samp{\B} in regexp | |
463 | matches the empty string, but @emph{not} at the beginning or | |
464 | end of a word. | |
465 | ||
466 | @item \< | |
467 | @cindex @samp{\<} in regexp | |
468 | matches the empty string, but only at the beginning of a word. | |
469 | ||
470 | @item \> | |
471 | @cindex @samp{\>} in regexp | |
472 | matches the empty string, but only at the end of a word. | |
473 | @end table | |
474 | ||
475 | @kindex invalid-regexp | |
476 | Not every string is a valid regular expression. For example, a string | |
477 | with unbalanced square brackets is invalid (with a few exceptions, such | |
61cfa852 | 478 | as @samp{[]]}), and so is a string that ends with a single @samp{\}. If |
7015aca4 RS |
479 | an invalid regular expression is passed to any of the search functions, |
480 | an @code{invalid-regexp} error is signaled. | |
481 | ||
482 | @defun regexp-quote string | |
483 | This function returns a regular expression string that matches exactly | |
484 | @var{string} and nothing else. This allows you to request an exact | |
485 | string match when calling a function that wants a regular expression. | |
486 | ||
487 | @example | |
488 | @group | |
489 | (regexp-quote "^The cat$") | |
490 | @result{} "\\^The cat\\$" | |
491 | @end group | |
492 | @end example | |
493 | ||
494 | One use of @code{regexp-quote} is to combine an exact string match with | |
495 | context described as a regular expression. For example, this searches | |
61cfa852 | 496 | for the string that is the value of @code{string}, surrounded by |
7015aca4 RS |
497 | whitespace: |
498 | ||
499 | @example | |
500 | @group | |
501 | (re-search-forward | |
61cfa852 | 502 | (concat "\\s-" (regexp-quote string) "\\s-")) |
7015aca4 RS |
503 | @end group |
504 | @end example | |
505 | @end defun | |
506 | ||
507 | @node Regexp Example | |
508 | @comment node-name, next, previous, up | |
509 | @subsection Complex Regexp Example | |
510 | ||
511 | Here is a complicated regexp, used by Emacs to recognize the end of a | |
512 | sentence together with any whitespace that follows. It is the value of | |
513 | the variable @code{sentence-end}. | |
514 | ||
515 | First, we show the regexp as a string in Lisp syntax to distinguish | |
516 | spaces from tab characters. The string constant begins and ends with a | |
517 | double-quote. @samp{\"} stands for a double-quote as part of the | |
518 | string, @samp{\\} for a backslash as part of the string, @samp{\t} for a | |
519 | tab and @samp{\n} for a newline. | |
520 | ||
521 | @example | |
522 | "[.?!][]\"')@}]*\\($\\| $\\|\t\\| \\)[ \t\n]*" | |
523 | @end example | |
524 | ||
525 | In contrast, if you evaluate the variable @code{sentence-end}, you | |
526 | will see the following: | |
527 | ||
528 | @example | |
529 | @group | |
530 | sentence-end | |
531 | @result{} | |
532 | "[.?!][]\"')@}]*\\($\\| $\\| \\| \\)[ | |
533 | ]*" | |
534 | @end group | |
535 | @end example | |
536 | ||
537 | @noindent | |
538 | In this output, tab and newline appear as themselves. | |
539 | ||
540 | This regular expression contains four parts in succession and can be | |
541 | deciphered as follows: | |
542 | ||
543 | @table @code | |
544 | @item [.?!] | |
7fd1911a RS |
545 | The first part of the pattern is a character set that matches any one of |
546 | three characters: period, question mark, and exclamation mark. The | |
7015aca4 RS |
547 | match must begin with one of these three characters. |
548 | ||
549 | @item []\"')@}]* | |
550 | The second part of the pattern matches any closing braces and quotation | |
551 | marks, zero or more of them, that may follow the period, question mark | |
552 | or exclamation mark. The @code{\"} is Lisp syntax for a double-quote in | |
553 | a string. The @samp{*} at the end indicates that the immediately | |
554 | preceding regular expression (a character set, in this case) may be | |
555 | repeated zero or more times. | |
556 | ||
7fd1911a | 557 | @item \\($\\|@ $\\|\t\\|@ @ \\) |
7015aca4 RS |
558 | The third part of the pattern matches the whitespace that follows the |
559 | end of a sentence: the end of a line, or a tab, or two spaces. The | |
560 | double backslashes mark the parentheses and vertical bars as regular | |
7fd1911a | 561 | expression syntax; the parentheses delimit a group and the vertical bars |
7015aca4 RS |
562 | separate alternatives. The dollar sign is used to match the end of a |
563 | line. | |
564 | ||
565 | @item [ \t\n]* | |
566 | Finally, the last part of the pattern matches any additional whitespace | |
567 | beyond the minimum needed to end a sentence. | |
568 | @end table | |
569 | ||
570 | @node Regexp Search | |
571 | @section Regular Expression Searching | |
572 | @cindex regular expression searching | |
573 | @cindex regexp searching | |
574 | @cindex searching for regexp | |
575 | ||
576 | In GNU Emacs, you can search for the next match for a regexp either | |
577 | incrementally or not. For incremental search commands, see @ref{Regexp | |
578 | Search, , Regular Expression Search, emacs, The GNU Emacs Manual}. Here | |
579 | we describe only the search functions useful in programs. The principal | |
580 | one is @code{re-search-forward}. | |
581 | ||
582 | @deffn Command re-search-forward regexp &optional limit noerror repeat | |
583 | This function searches forward in the current buffer for a string of | |
584 | text that is matched by the regular expression @var{regexp}. The | |
585 | function skips over any amount of text that is not matched by | |
586 | @var{regexp}, and leaves point at the end of the first match found. | |
587 | It returns the new value of point. | |
588 | ||
589 | If @var{limit} is non-@code{nil} (it must be a position in the current | |
590 | buffer), then it is the upper bound to the search. No match extending | |
591 | after that position is accepted. | |
592 | ||
593 | What happens when the search fails depends on the value of | |
594 | @var{noerror}. If @var{noerror} is @code{nil}, a @code{search-failed} | |
595 | error is signaled. If @var{noerror} is @code{t}, | |
596 | @code{re-search-forward} does nothing and returns @code{nil}. If | |
597 | @var{noerror} is neither @code{nil} nor @code{t}, then | |
598 | @code{re-search-forward} moves point to @var{limit} (or the end of the | |
599 | buffer) and returns @code{nil}. | |
600 | ||
601 | If @var{repeat} is supplied (it must be a positive number), then the | |
602 | search is repeated that many times (each time starting at the end of the | |
603 | previous time's match). If these successive searches succeed, the | |
604 | function succeeds, moving point and returning its new value. Otherwise | |
605 | the search fails. | |
606 | ||
607 | In the following example, point is initially before the @samp{T}. | |
608 | Evaluating the search call moves point to the end of that line (between | |
609 | the @samp{t} of @samp{hat} and the newline). | |
610 | ||
611 | @example | |
612 | @group | |
613 | ---------- Buffer: foo ---------- | |
614 | I read "@point{}The cat in the hat | |
615 | comes back" twice. | |
616 | ---------- Buffer: foo ---------- | |
617 | @end group | |
618 | ||
619 | @group | |
620 | (re-search-forward "[a-z]+" nil t 5) | |
621 | @result{} 27 | |
622 | ||
623 | ---------- Buffer: foo ---------- | |
624 | I read "The cat in the hat@point{} | |
625 | comes back" twice. | |
626 | ---------- Buffer: foo ---------- | |
627 | @end group | |
628 | @end example | |
629 | @end deffn | |
630 | ||
631 | @deffn Command re-search-backward regexp &optional limit noerror repeat | |
632 | This function searches backward in the current buffer for a string of | |
633 | text that is matched by the regular expression @var{regexp}, leaving | |
634 | point at the beginning of the first text found. | |
635 | ||
7fd1911a RS |
636 | This function is analogous to @code{re-search-forward}, but they are not |
637 | simple mirror images. @code{re-search-forward} finds the match whose | |
638 | beginning is as close as possible to the starting point. If | |
639 | @code{re-search-backward} were a perfect mirror image, it would find the | |
640 | match whose end is as close as possible. However, in fact it finds the | |
641 | match whose beginning is as close as possible. The reason is that | |
642 | matching a regular expression at a given spot always works from | |
643 | beginning to end, and starts at a specified beginning position. | |
7015aca4 RS |
644 | |
645 | A true mirror-image of @code{re-search-forward} would require a special | |
646 | feature for matching regexps from end to beginning. It's not worth the | |
647 | trouble of implementing that. | |
648 | @end deffn | |
649 | ||
650 | @defun string-match regexp string &optional start | |
651 | This function returns the index of the start of the first match for | |
652 | the regular expression @var{regexp} in @var{string}, or @code{nil} if | |
653 | there is no match. If @var{start} is non-@code{nil}, the search starts | |
654 | at that index in @var{string}. | |
655 | ||
656 | For example, | |
657 | ||
658 | @example | |
659 | @group | |
660 | (string-match | |
661 | "quick" "The quick brown fox jumped quickly.") | |
662 | @result{} 4 | |
663 | @end group | |
664 | @group | |
665 | (string-match | |
666 | "quick" "The quick brown fox jumped quickly." 8) | |
667 | @result{} 27 | |
668 | @end group | |
669 | @end example | |
670 | ||
671 | @noindent | |
672 | The index of the first character of the | |
673 | string is 0, the index of the second character is 1, and so on. | |
674 | ||
675 | After this function returns, the index of the first character beyond | |
676 | the match is available as @code{(match-end 0)}. @xref{Match Data}. | |
677 | ||
678 | @example | |
679 | @group | |
680 | (string-match | |
681 | "quick" "The quick brown fox jumped quickly." 8) | |
682 | @result{} 27 | |
683 | @end group | |
684 | ||
685 | @group | |
686 | (match-end 0) | |
687 | @result{} 32 | |
688 | @end group | |
689 | @end example | |
690 | @end defun | |
691 | ||
692 | @defun looking-at regexp | |
693 | This function determines whether the text in the current buffer directly | |
694 | following point matches the regular expression @var{regexp}. ``Directly | |
695 | following'' means precisely that: the search is ``anchored'' and it can | |
696 | succeed only starting with the first character following point. The | |
697 | result is @code{t} if so, @code{nil} otherwise. | |
698 | ||
699 | This function does not move point, but it updates the match data, which | |
700 | you can access using @code{match-beginning} and @code{match-end}. | |
701 | @xref{Match Data}. | |
702 | ||
703 | In this example, point is located directly before the @samp{T}. If it | |
704 | were anywhere else, the result would be @code{nil}. | |
705 | ||
706 | @example | |
707 | @group | |
708 | ---------- Buffer: foo ---------- | |
709 | I read "@point{}The cat in the hat | |
710 | comes back" twice. | |
711 | ---------- Buffer: foo ---------- | |
712 | ||
713 | (looking-at "The cat in the hat$") | |
714 | @result{} t | |
715 | @end group | |
716 | @end example | |
717 | @end defun | |
718 | ||
22697dac KH |
719 | @node POSIX Regexps |
720 | @section POSIX Regular Expression Searching | |
721 | ||
722 | The usual regular expression functions do backtracking when necessary | |
723 | to handle the @samp{\|} and repetition constructs, but they continue | |
724 | this only until they find @emph{some} match. Then they succeed and | |
725 | report the first match found. | |
726 | ||
727 | This section describes alternative search functions which perform the | |
728 | full backtracking specified by the POSIX standard for regular expression | |
729 | matching. They continue backtracking until they have tried all | |
730 | possibilities and found all matches, so they can report the longest | |
731 | match, as required by POSIX. This is much slower, so use these | |
732 | functions only when you really need the longest match. | |
733 | ||
734 | In Emacs versions prior to 19.29, these functions did not exist, and | |
735 | the functions described above implemented full POSIX backtracking. | |
736 | ||
737 | @defun posix-search-forward regexp &optional limit noerror repeat | |
738 | This is like @code{re-search-forward} except that it performs the full | |
739 | backtracking specified by the POSIX standard for regular expression | |
740 | matching. | |
741 | @end defun | |
742 | ||
743 | @defun posix-search-backward regexp &optional limit noerror repeat | |
744 | This is like @code{re-search-backward} except that it performs the full | |
745 | backtracking specified by the POSIX standard for regular expression | |
746 | matching. | |
747 | @end defun | |
748 | ||
749 | @defun posix-looking-at regexp | |
750 | This is like @code{looking-at} except that it performs the full | |
751 | backtracking specified by the POSIX standard for regular expression | |
752 | matching. | |
753 | @end defun | |
754 | ||
755 | @defun posix-string-match regexp string &optional start | |
756 | This is like @code{string-match} except that it performs the full | |
757 | backtracking specified by the POSIX standard for regular expression | |
758 | matching. | |
759 | @end defun | |
760 | ||
7015aca4 RS |
761 | @ignore |
762 | @deffn Command delete-matching-lines regexp | |
763 | This function is identical to @code{delete-non-matching-lines}, save | |
764 | that it deletes what @code{delete-non-matching-lines} keeps. | |
765 | ||
766 | In the example below, point is located on the first line of text. | |
767 | ||
768 | @example | |
769 | @group | |
770 | ---------- Buffer: foo ---------- | |
771 | We hold these truths | |
772 | to be self-evident, | |
773 | that all men are created | |
774 | equal, and that they are | |
775 | ---------- Buffer: foo ---------- | |
776 | @end group | |
777 | ||
778 | @group | |
779 | (delete-matching-lines "the") | |
780 | @result{} nil | |
781 | ||
782 | ---------- Buffer: foo ---------- | |
783 | to be self-evident, | |
784 | that all men are created | |
785 | ---------- Buffer: foo ---------- | |
786 | @end group | |
787 | @end example | |
788 | @end deffn | |
789 | ||
790 | @deffn Command flush-lines regexp | |
791 | This function is the same as @code{delete-matching-lines}. | |
792 | @end deffn | |
793 | ||
794 | @defun delete-non-matching-lines regexp | |
795 | This function deletes all lines following point which don't | |
796 | contain a match for the regular expression @var{regexp}. | |
797 | @end defun | |
798 | ||
799 | @deffn Command keep-lines regexp | |
800 | This function is the same as @code{delete-non-matching-lines}. | |
801 | @end deffn | |
802 | ||
803 | @deffn Command how-many regexp | |
804 | This function counts the number of matches for @var{regexp} there are in | |
805 | the current buffer following point. It prints this number in | |
806 | the echo area, returning the string printed. | |
807 | @end deffn | |
808 | ||
809 | @deffn Command count-matches regexp | |
810 | This function is a synonym of @code{how-many}. | |
811 | @end deffn | |
812 | ||
813 | @deffn Command list-matching-lines regexp nlines | |
814 | This function is a synonym of @code{occur}. | |
815 | Show all lines following point containing a match for @var{regexp}. | |
816 | Display each line with @var{nlines} lines before and after, | |
817 | or @code{-}@var{nlines} before if @var{nlines} is negative. | |
818 | @var{nlines} defaults to @code{list-matching-lines-default-context-lines}. | |
819 | Interactively it is the prefix arg. | |
820 | ||
821 | The lines are shown in a buffer named @samp{*Occur*}. | |
822 | It serves as a menu to find any of the occurrences in this buffer. | |
823 | @kbd{C-h m} (@code{describe-mode} in that buffer gives help. | |
824 | @end deffn | |
825 | ||
826 | @defopt list-matching-lines-default-context-lines | |
827 | Default value is 0. | |
828 | Default number of context lines to include around a @code{list-matching-lines} | |
829 | match. A negative number means to include that many lines before the match. | |
830 | A positive number means to include that many lines both before and after. | |
831 | @end defopt | |
832 | @end ignore | |
833 | ||
834 | @node Search and Replace | |
835 | @section Search and Replace | |
836 | @cindex replacement | |
837 | ||
838 | @defun perform-replace from-string replacements query-flag regexp-flag delimited-flag &optional repeat-count map | |
839 | This function is the guts of @code{query-replace} and related commands. | |
840 | It searches for occurrences of @var{from-string} and replaces some or | |
841 | all of them. If @var{query-flag} is @code{nil}, it replaces all | |
842 | occurrences; otherwise, it asks the user what to do about each one. | |
843 | ||
844 | If @var{regexp-flag} is non-@code{nil}, then @var{from-string} is | |
845 | considered a regular expression; otherwise, it must match literally. If | |
846 | @var{delimited-flag} is non-@code{nil}, then only replacements | |
847 | surrounded by word boundaries are considered. | |
848 | ||
849 | The argument @var{replacements} specifies what to replace occurrences | |
850 | with. If it is a string, that string is used. It can also be a list of | |
851 | strings, to be used in cyclic order. | |
852 | ||
bda144f4 MW |
853 | If @var{repeat-count} is non-@code{nil}, it should be an integer. Then |
854 | it specifies how many times to use each of the strings in the | |
855 | @var{replacements} list before advancing cyclicly to the next one. | |
7015aca4 RS |
856 | |
857 | Normally, the keymap @code{query-replace-map} defines the possible user | |
7fd1911a RS |
858 | responses for queries. The argument @var{map}, if non-@code{nil}, is a |
859 | keymap to use instead of @code{query-replace-map}. | |
7015aca4 RS |
860 | @end defun |
861 | ||
862 | @defvar query-replace-map | |
863 | This variable holds a special keymap that defines the valid user | |
864 | responses for @code{query-replace} and related functions, as well as | |
865 | @code{y-or-n-p} and @code{map-y-or-n-p}. It is unusual in two ways: | |
866 | ||
867 | @itemize @bullet | |
868 | @item | |
869 | The ``key bindings'' are not commands, just symbols that are meaningful | |
870 | to the functions that use this map. | |
871 | ||
872 | @item | |
873 | Prefix keys are not supported; each key binding must be for a single event | |
874 | key sequence. This is because the functions don't use read key sequence to | |
875 | get the input; instead, they read a single event and look it up ``by hand.'' | |
876 | @end itemize | |
877 | @end defvar | |
878 | ||
879 | Here are the meaningful ``bindings'' for @code{query-replace-map}. | |
880 | Several of them are meaningful only for @code{query-replace} and | |
881 | friends. | |
882 | ||
883 | @table @code | |
884 | @item act | |
885 | Do take the action being considered---in other words, ``yes.'' | |
886 | ||
887 | @item skip | |
888 | Do not take action for this question---in other words, ``no.'' | |
889 | ||
890 | @item exit | |
7fd1911a RS |
891 | Answer this question ``no,'' and give up on the entire series of |
892 | questions, assuming that the answers will be ``no.'' | |
7015aca4 RS |
893 | |
894 | @item act-and-exit | |
7fd1911a RS |
895 | Answer this question ``yes,'' and give up on the entire series of |
896 | questions, assuming that subsequent answers will be ``no.'' | |
7015aca4 RS |
897 | |
898 | @item act-and-show | |
899 | Answer this question ``yes,'' but show the results---don't advance yet | |
900 | to the next question. | |
901 | ||
902 | @item automatic | |
903 | Answer this question and all subsequent questions in the series with | |
904 | ``yes,'' without further user interaction. | |
905 | ||
906 | @item backup | |
907 | Move back to the previous place that a question was asked about. | |
908 | ||
909 | @item edit | |
910 | Enter a recursive edit to deal with this question---instead of any | |
911 | other action that would normally be taken. | |
912 | ||
913 | @item delete-and-edit | |
914 | Delete the text being considered, then enter a recursive edit to replace | |
915 | it. | |
916 | ||
917 | @item recenter | |
918 | Redisplay and center the window, then ask the same question again. | |
919 | ||
920 | @item quit | |
921 | Perform a quit right away. Only @code{y-or-n-p} and related functions | |
922 | use this answer. | |
923 | ||
924 | @item help | |
925 | Display some help, then ask again. | |
926 | @end table | |
927 | ||
928 | @node Match Data | |
929 | @section The Match Data | |
930 | @cindex match data | |
931 | ||
932 | Emacs keeps track of the positions of the start and end of segments of | |
933 | text found during a regular expression search. This means, for example, | |
934 | that you can search for a complex pattern, such as a date in an Rmail | |
935 | message, and then extract parts of the match under control of the | |
936 | pattern. | |
937 | ||
938 | Because the match data normally describe the most recent search only, | |
939 | you must be careful not to do another search inadvertently between the | |
940 | search you wish to refer back to and the use of the match data. If you | |
941 | can't avoid another intervening search, you must save and restore the | |
942 | match data around it, to prevent it from being overwritten. | |
943 | ||
944 | @menu | |
945 | * Simple Match Data:: Accessing single items of match data, | |
946 | such as where a particular subexpression started. | |
947 | * Replacing Match:: Replacing a substring that was matched. | |
948 | * Entire Match Data:: Accessing the entire match data at once, as a list. | |
949 | * Saving Match Data:: Saving and restoring the match data. | |
950 | @end menu | |
951 | ||
952 | @node Simple Match Data | |
953 | @subsection Simple Match Data Access | |
954 | ||
22697dac KH |
955 | This section explains how to use the match data to find out what was |
956 | matched by the last search or match operation. | |
957 | ||
958 | You can ask about the entire matching text, or about a particular | |
959 | parenthetical subexpression of a regular expression. The @var{count} | |
960 | argument in the functions below specifies which. If @var{count} is | |
961 | zero, you are asking about the entire match. If @var{count} is | |
962 | positive, it specifies which subexpression you want. | |
963 | ||
964 | Recall that the subexpressions of a regular expression are those | |
965 | expressions grouped with escaped parentheses, @samp{\(@dots{}\)}. The | |
966 | @var{count}th subexpression is found by counting occurrences of | |
967 | @samp{\(} from the beginning of the whole regular expression. The first | |
968 | subexpression is numbered 1, the second 2, and so on. Only regular | |
969 | expressions can have subexpressions---after a simple string search, the | |
970 | only information available is about the entire match. | |
971 | ||
972 | @defun match-string count &optional in-string | |
973 | This function returns, as a string, the text matched in the last search | |
974 | or match operation. It returns the entire text if @var{count} is zero, | |
975 | or just the portion corresponding to the @var{count}th parenthetical | |
976 | subexpression, if @var{count} is positive. If @var{count} is out of | |
bfe721d1 KH |
977 | range, or if that subexpression didn't match anything, the value is |
978 | @code{nil}. | |
22697dac KH |
979 | |
980 | If the last such operation was done against a string with | |
981 | @code{string-match}, then you should pass the same string as the | |
982 | argument @var{in-string}. Otherwise, after a buffer search or match, | |
983 | you should omit @var{in-string} or pass @code{nil} for it; but you | |
984 | should make sure that the current buffer when you call | |
985 | @code{match-string} is the one in which you did the searching or | |
986 | matching. | |
987 | @end defun | |
7015aca4 RS |
988 | |
989 | @defun match-beginning count | |
990 | This function returns the position of the start of text matched by the | |
991 | last regular expression searched for, or a subexpression of it. | |
992 | ||
7fd1911a | 993 | If @var{count} is zero, then the value is the position of the start of |
eaac2be1 | 994 | the entire match. Otherwise, @var{count} specifies a subexpression in |
22697dac KH |
995 | the regular expresion, and the value of the function is the starting |
996 | position of the match for that subexpression. | |
997 | ||
998 | The value is @code{nil} for a subexpression inside a @samp{\|} | |
999 | alternative that wasn't used in the match. | |
7015aca4 RS |
1000 | @end defun |
1001 | ||
1002 | @defun match-end count | |
22697dac KH |
1003 | This function is like @code{match-beginning} except that it returns the |
1004 | position of the end of the match, rather than the position of the | |
1005 | beginning. | |
7015aca4 RS |
1006 | @end defun |
1007 | ||
1008 | Here is an example of using the match data, with a comment showing the | |
1009 | positions within the text: | |
1010 | ||
1011 | @example | |
1012 | @group | |
1013 | (string-match "\\(qu\\)\\(ick\\)" | |
1014 | "The quick fox jumped quickly.") | |
1015 | ;0123456789 | |
1016 | @result{} 4 | |
1017 | @end group | |
1018 | ||
22697dac KH |
1019 | @group |
1020 | (match-string 0 "The quick fox jumped quickly.") | |
1021 | @result{} "quick" | |
1022 | (match-string 1 "The quick fox jumped quickly.") | |
1023 | @result{} "qu" | |
1024 | (match-string 2 "The quick fox jumped quickly.") | |
1025 | @result{} "ick" | |
1026 | @end group | |
1027 | ||
7015aca4 RS |
1028 | @group |
1029 | (match-beginning 1) ; @r{The beginning of the match} | |
1030 | @result{} 4 ; @r{with @samp{qu} is at index 4.} | |
1031 | @end group | |
1032 | ||
1033 | @group | |
1034 | (match-beginning 2) ; @r{The beginning of the match} | |
1035 | @result{} 6 ; @r{with @samp{ick} is at index 6.} | |
1036 | @end group | |
1037 | ||
1038 | @group | |
1039 | (match-end 1) ; @r{The end of the match} | |
1040 | @result{} 6 ; @r{with @samp{qu} is at index 6.} | |
1041 | ||
1042 | (match-end 2) ; @r{The end of the match} | |
1043 | @result{} 9 ; @r{with @samp{ick} is at index 9.} | |
1044 | @end group | |
1045 | @end example | |
1046 | ||
1047 | Here is another example. Point is initially located at the beginning | |
1048 | of the line. Searching moves point to between the space and the word | |
1049 | @samp{in}. The beginning of the entire match is at the 9th character of | |
1050 | the buffer (@samp{T}), and the beginning of the match for the first | |
1051 | subexpression is at the 13th character (@samp{c}). | |
1052 | ||
1053 | @example | |
1054 | @group | |
1055 | (list | |
1056 | (re-search-forward "The \\(cat \\)") | |
1057 | (match-beginning 0) | |
1058 | (match-beginning 1)) | |
7fd1911a | 1059 | @result{} (9 9 13) |
7015aca4 RS |
1060 | @end group |
1061 | ||
1062 | @group | |
1063 | ---------- Buffer: foo ---------- | |
1064 | I read "The cat @point{}in the hat comes back" twice. | |
1065 | ^ ^ | |
1066 | 9 13 | |
1067 | ---------- Buffer: foo ---------- | |
1068 | @end group | |
1069 | @end example | |
1070 | ||
1071 | @noindent | |
1072 | (In this case, the index returned is a buffer position; the first | |
1073 | character of the buffer counts as 1.) | |
1074 | ||
1075 | @node Replacing Match | |
1076 | @subsection Replacing the Text That Matched | |
1077 | ||
1078 | This function replaces the text matched by the last search with | |
1079 | @var{replacement}. | |
1080 | ||
1081 | @cindex case in replacements | |
d544c776 | 1082 | @defun replace-match replacement &optional fixedcase literal string subexp |
22697dac KH |
1083 | This function replaces the text in the buffer (or in @var{string}) that |
1084 | was matched by the last search. It replaces that text with | |
1085 | @var{replacement}. | |
1086 | ||
bfe721d1 KH |
1087 | If you did the last search in a buffer, you should specify @code{nil} |
1088 | for @var{string}. Then @code{replace-match} does the replacement by | |
1089 | editing the buffer; it leaves point at the end of the replacement text, | |
1090 | and returns @code{t}. | |
1091 | ||
1092 | If you did the search in a string, pass the same string as @var{string}. | |
1093 | Then @code{replace-match} does the replacement by constructing and | |
1094 | returning a new string. | |
7015aca4 RS |
1095 | |
1096 | If @var{fixedcase} is non-@code{nil}, then the case of the replacement | |
1097 | text is not changed; otherwise, the replacement text is converted to a | |
1098 | different case depending upon the capitalization of the text to be | |
1099 | replaced. If the original text is all upper case, the replacement text | |
a890e1b0 RS |
1100 | is converted to upper case. If the first word of the original text is |
1101 | capitalized, then the first word of the replacement text is capitalized. | |
1102 | If the original text contains just one word, and that word is a capital | |
1103 | letter, @code{replace-match} considers this a capitalized first word | |
1104 | rather than all upper case. | |
7015aca4 | 1105 | |
7fd1911a RS |
1106 | If @code{case-replace} is @code{nil}, then case conversion is not done, |
1107 | regardless of the value of @var{fixed-case}. @xref{Searching and Case}. | |
1108 | ||
7015aca4 RS |
1109 | If @var{literal} is non-@code{nil}, then @var{replacement} is inserted |
1110 | exactly as it is, the only alterations being case changes as needed. | |
1111 | If it is @code{nil} (the default), then the character @samp{\} is treated | |
1112 | specially. If a @samp{\} appears in @var{replacement}, then it must be | |
1113 | part of one of the following sequences: | |
1114 | ||
1115 | @table @asis | |
1116 | @item @samp{\&} | |
1117 | @cindex @samp{&} in replacement | |
1118 | @samp{\&} stands for the entire text being replaced. | |
1119 | ||
1120 | @item @samp{\@var{n}} | |
1121 | @cindex @samp{\@var{n}} in replacement | |
7fd1911a RS |
1122 | @samp{\@var{n}}, where @var{n} is a digit, stands for the text that |
1123 | matched the @var{n}th subexpression in the original regexp. | |
1124 | Subexpressions are those expressions grouped inside @samp{\(@dots{}\)}. | |
7015aca4 RS |
1125 | |
1126 | @item @samp{\\} | |
1127 | @cindex @samp{\} in replacement | |
1128 | @samp{\\} stands for a single @samp{\} in the replacement text. | |
1129 | @end table | |
d544c776 RS |
1130 | |
1131 | If @var{subexp} is non-@code{nil}, that says to replace just | |
1132 | subexpression number @var{subexp} of the regexp that was matched, not | |
1133 | the entire match. For example, after matching @samp{foo \(ba*r\)}, | |
1134 | calling @code{replace-match} with 1 as @var{subexp} means to replace | |
1135 | just the text that matched @samp{\(ba*r\)}. | |
7015aca4 RS |
1136 | @end defun |
1137 | ||
1138 | @node Entire Match Data | |
1139 | @subsection Accessing the Entire Match Data | |
1140 | ||
1141 | The functions @code{match-data} and @code{set-match-data} read or | |
1142 | write the entire match data, all at once. | |
1143 | ||
1144 | @defun match-data | |
1145 | This function returns a newly constructed list containing all the | |
1146 | information on what text the last search matched. Element zero is the | |
1147 | position of the beginning of the match for the whole expression; element | |
1148 | one is the position of the end of the match for the expression. The | |
1149 | next two elements are the positions of the beginning and end of the | |
1150 | match for the first subexpression, and so on. In general, element | |
1151 | @ifinfo | |
1152 | number 2@var{n} | |
1153 | @end ifinfo | |
1154 | @tex | |
1155 | number {\mathsurround=0pt $2n$} | |
1156 | @end tex | |
1157 | corresponds to @code{(match-beginning @var{n})}; and | |
1158 | element | |
1159 | @ifinfo | |
1160 | number 2@var{n} + 1 | |
1161 | @end ifinfo | |
1162 | @tex | |
1163 | number {\mathsurround=0pt $2n+1$} | |
1164 | @end tex | |
1165 | corresponds to @code{(match-end @var{n})}. | |
1166 | ||
1167 | All the elements are markers or @code{nil} if matching was done on a | |
1168 | buffer, and all are integers or @code{nil} if matching was done on a | |
1169 | string with @code{string-match}. (In Emacs 18 and earlier versions, | |
1170 | markers were used even for matching on a string, except in the case | |
1171 | of the integer 0.) | |
1172 | ||
1173 | As always, there must be no possibility of intervening searches between | |
1174 | the call to a search function and the call to @code{match-data} that is | |
1175 | intended to access the match data for that search. | |
1176 | ||
1177 | @example | |
1178 | @group | |
1179 | (match-data) | |
1180 | @result{} (#<marker at 9 in foo> | |
1181 | #<marker at 17 in foo> | |
1182 | #<marker at 13 in foo> | |
1183 | #<marker at 17 in foo>) | |
1184 | @end group | |
1185 | @end example | |
1186 | @end defun | |
1187 | ||
1188 | @defun set-match-data match-list | |
1189 | This function sets the match data from the elements of @var{match-list}, | |
1190 | which should be a list that was the value of a previous call to | |
1191 | @code{match-data}. | |
1192 | ||
1193 | If @var{match-list} refers to a buffer that doesn't exist, you don't get | |
1194 | an error; that sets the match data in a meaningless but harmless way. | |
1195 | ||
1196 | @findex store-match-data | |
1197 | @code{store-match-data} is an alias for @code{set-match-data}. | |
1198 | @end defun | |
1199 | ||
1200 | @node Saving Match Data | |
1201 | @subsection Saving and Restoring the Match Data | |
1202 | ||
d1280259 RS |
1203 | When you call a function that may do a search, you may need to save |
1204 | and restore the match data around that call, if you want to preserve the | |
1205 | match data from an earlier search for later use. Here is an example | |
1206 | that shows the problem that arises if you fail to save the match data: | |
7015aca4 RS |
1207 | |
1208 | @example | |
1209 | @group | |
1210 | (re-search-forward "The \\(cat \\)") | |
1211 | @result{} 48 | |
1212 | (foo) ; @r{Perhaps @code{foo} does} | |
1213 | ; @r{more searching.} | |
1214 | (match-end 0) | |
1215 | @result{} 61 ; @r{Unexpected result---not 48!} | |
1216 | @end group | |
1217 | @end example | |
1218 | ||
d1280259 | 1219 | You can save and restore the match data with @code{save-match-data}: |
7015aca4 | 1220 | |
bfe721d1 | 1221 | @defmac save-match-data body@dots{} |
7015aca4 | 1222 | This special form executes @var{body}, saving and restoring the match |
d1280259 | 1223 | data around it. |
bfe721d1 | 1224 | @end defmac |
7015aca4 RS |
1225 | |
1226 | You can use @code{set-match-data} together with @code{match-data} to | |
1227 | imitate the effect of the special form @code{save-match-data}. This is | |
1228 | useful for writing code that can run in Emacs 18. Here is how: | |
1229 | ||
1230 | @example | |
1231 | @group | |
1232 | (let ((data (match-data))) | |
1233 | (unwind-protect | |
1234 | @dots{} ; @r{May change the original match data.} | |
1235 | (set-match-data data))) | |
1236 | @end group | |
1237 | @end example | |
1238 | ||
d1280259 RS |
1239 | Emacs automatically saves and restores the match data when it runs |
1240 | process filter functions (@pxref{Filter Functions}) and process | |
1241 | sentinels (@pxref{Sentinels}). | |
1242 | ||
7015aca4 RS |
1243 | @ignore |
1244 | Here is a function which restores the match data provided the buffer | |
1245 | associated with it still exists. | |
1246 | ||
1247 | @smallexample | |
1248 | @group | |
1249 | (defun restore-match-data (data) | |
1250 | @c It is incorrect to split the first line of a doc string. | |
1251 | @c If there's a problem here, it should be solved in some other way. | |
1252 | "Restore the match data DATA unless the buffer is missing." | |
1253 | (catch 'foo | |
1254 | (let ((d data)) | |
1255 | @end group | |
1256 | (while d | |
1257 | (and (car d) | |
1258 | (null (marker-buffer (car d))) | |
1259 | @group | |
1260 | ;; @file{match-data} @r{buffer is deleted.} | |
1261 | (throw 'foo nil)) | |
1262 | (setq d (cdr d))) | |
1263 | (set-match-data data)))) | |
1264 | @end group | |
1265 | @end smallexample | |
1266 | @end ignore | |
1267 | ||
1268 | @node Searching and Case | |
1269 | @section Searching and Case | |
1270 | @cindex searching and case | |
1271 | ||
1272 | By default, searches in Emacs ignore the case of the text they are | |
1273 | searching through; if you specify searching for @samp{FOO}, then | |
1274 | @samp{Foo} or @samp{foo} is also considered a match. Regexps, and in | |
1275 | particular character sets, are included: thus, @samp{[aB]} would match | |
1276 | @samp{a} or @samp{A} or @samp{b} or @samp{B}. | |
1277 | ||
1278 | If you do not want this feature, set the variable | |
1279 | @code{case-fold-search} to @code{nil}. Then all letters must match | |
7fd1911a RS |
1280 | exactly, including case. This is a buffer-local variable; altering the |
1281 | variable affects only the current buffer. (@xref{Intro to | |
7015aca4 RS |
1282 | Buffer-Local}.) Alternatively, you may change the value of |
1283 | @code{default-case-fold-search}, which is the default value of | |
1284 | @code{case-fold-search} for buffers that do not override it. | |
1285 | ||
1286 | Note that the user-level incremental search feature handles case | |
1287 | distinctions differently. When given a lower case letter, it looks for | |
1288 | a match of either case, but when given an upper case letter, it looks | |
1289 | for an upper case letter only. But this has nothing to do with the | |
1290 | searching functions Lisp functions use. | |
1291 | ||
1292 | @defopt case-replace | |
7fd1911a RS |
1293 | This variable determines whether the replacement functions should |
1294 | preserve case. If the variable is @code{nil}, that means to use the | |
1295 | replacement text verbatim. A non-@code{nil} value means to convert the | |
1296 | case of the replacement text according to the text being replaced. | |
1297 | ||
1298 | The function @code{replace-match} is where this variable actually has | |
1299 | its effect. @xref{Replacing Match}. | |
7015aca4 RS |
1300 | @end defopt |
1301 | ||
1302 | @defopt case-fold-search | |
1303 | This buffer-local variable determines whether searches should ignore | |
1304 | case. If the variable is @code{nil} they do not ignore case; otherwise | |
1305 | they do ignore case. | |
1306 | @end defopt | |
1307 | ||
1308 | @defvar default-case-fold-search | |
1309 | The value of this variable is the default value for | |
1310 | @code{case-fold-search} in buffers that do not override it. This is the | |
1311 | same as @code{(default-value 'case-fold-search)}. | |
1312 | @end defvar | |
1313 | ||
1314 | @node Standard Regexps | |
1315 | @section Standard Regular Expressions Used in Editing | |
1316 | @cindex regexps used standardly in editing | |
1317 | @cindex standard regexps used in editing | |
1318 | ||
1319 | This section describes some variables that hold regular expressions | |
1320 | used for certain purposes in editing: | |
1321 | ||
1322 | @defvar page-delimiter | |
1323 | This is the regexp describing line-beginnings that separate pages. The | |
7fd1911a RS |
1324 | default value is @code{"^\014"} (i.e., @code{"^^L"} or @code{"^\C-l"}); |
1325 | this matches a line that starts with a formfeed character. | |
7015aca4 RS |
1326 | @end defvar |
1327 | ||
22697dac KH |
1328 | The following two regular expressions should @emph{not} assume the |
1329 | match always starts at the beginning of a line; they should not use | |
1330 | @samp{^} to anchor the match. Most often, the paragraph commands do | |
1331 | check for a match only at the beginning of a line, which means that | |
bfe721d1 KH |
1332 | @samp{^} would be superfluous. When there is a nonzero left margin, |
1333 | they accept matches that start after the left margin. In that case, a | |
1334 | @samp{^} would be incorrect. However, a @samp{^} is harmless in modes | |
1335 | where a left margin is never used. | |
22697dac | 1336 | |
7015aca4 RS |
1337 | @defvar paragraph-separate |
1338 | This is the regular expression for recognizing the beginning of a line | |
1339 | that separates paragraphs. (If you change this, you may have to | |
7fd1911a | 1340 | change @code{paragraph-start} also.) The default value is |
22697dac KH |
1341 | @w{@code{"[@ \t\f]*$"}}, which matches a line that consists entirely of |
1342 | spaces, tabs, and form feeds (after its left margin). | |
7015aca4 RS |
1343 | @end defvar |
1344 | ||
1345 | @defvar paragraph-start | |
1346 | This is the regular expression for recognizing the beginning of a line | |
1347 | that starts @emph{or} separates paragraphs. The default value is | |
22697dac KH |
1348 | @w{@code{"[@ \t\n\f]"}}, which matches a line starting with a space, tab, |
1349 | newline, or form feed (after its left margin). | |
7015aca4 RS |
1350 | @end defvar |
1351 | ||
1352 | @defvar sentence-end | |
1353 | This is the regular expression describing the end of a sentence. (All | |
1354 | paragraph boundaries also end sentences, regardless.) The default value | |
1355 | is: | |
1356 | ||
1357 | @example | |
7fd1911a | 1358 | "[.?!][]\"')@}]*\\($\\| $\\|\t\\| \\)[ \t\n]*" |
7015aca4 RS |
1359 | @end example |
1360 | ||
7fd1911a RS |
1361 | This means a period, question mark or exclamation mark, followed |
1362 | optionally by a closing parenthetical character, followed by tabs, | |
1363 | spaces or new lines. | |
7015aca4 RS |
1364 | |
1365 | For a detailed explanation of this regular expression, see @ref{Regexp | |
1366 | Example}. | |
1367 | @end defvar |