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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
73b0cd50 | 3 | @c Copyright (C) 1990-1995, 1998-1999, 2001-2011 |
d24880de | 4 | @c Free Software Foundation, Inc. |
b8d4c8d0 | 5 | @c See the file elisp.texi for copying conditions. |
6336d8c3 | 6 | @setfilename ../../info/searching |
b8d4c8d0 GM |
7 | @node Searching and Matching, Syntax Tables, Non-ASCII Characters, Top |
8 | @chapter Searching and Matching | |
9 | @cindex searching | |
10 | ||
11 | GNU Emacs provides two ways to search through a buffer for specified | |
12 | text: exact string searches and regular expression searches. After a | |
13 | regular expression search, you can examine the @dfn{match data} to | |
14 | determine which text matched the whole regular expression or various | |
15 | portions of it. | |
16 | ||
17 | @menu | |
18 | * String Search:: Search for an exact match. | |
19 | * Searching and Case:: Case-independent or case-significant searching. | |
20 | * Regular Expressions:: Describing classes of strings. | |
21 | * Regexp Search:: Searching for a match for a regexp. | |
22 | * POSIX Regexps:: Searching POSIX-style for the longest match. | |
23 | * Match Data:: Finding out which part of the text matched, | |
24 | after a string or regexp search. | |
d24880de | 25 | * Search and Replace:: Commands that loop, searching and replacing. |
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26 | * Standard Regexps:: Useful regexps for finding sentences, pages,... |
27 | @end menu | |
28 | ||
29 | The @samp{skip-chars@dots{}} functions also perform a kind of searching. | |
30 | @xref{Skipping Characters}. To search for changes in character | |
31 | properties, see @ref{Property Search}. | |
32 | ||
33 | @node String Search | |
34 | @section Searching for Strings | |
35 | @cindex string search | |
36 | ||
37 | These are the primitive functions for searching through the text in a | |
38 | buffer. They are meant for use in programs, but you may call them | |
39 | interactively. If you do so, they prompt for the search string; the | |
40 | arguments @var{limit} and @var{noerror} are @code{nil}, and @var{repeat} | |
41 | is 1. | |
42 | ||
43 | These search functions convert the search string to multibyte if the | |
44 | buffer is multibyte; they convert the search string to unibyte if the | |
45 | buffer is unibyte. @xref{Text Representations}. | |
46 | ||
47 | @deffn Command search-forward string &optional limit noerror repeat | |
48 | This function searches forward from point for an exact match for | |
49 | @var{string}. If successful, it sets point to the end of the occurrence | |
50 | found, and returns the new value of point. If no match is found, the | |
51 | value and side effects depend on @var{noerror} (see below). | |
52 | @c Emacs 19 feature | |
53 | ||
54 | In the following example, point is initially at the beginning of the | |
55 | line. Then @code{(search-forward "fox")} moves point after the last | |
56 | letter of @samp{fox}: | |
57 | ||
58 | @example | |
59 | @group | |
60 | ---------- Buffer: foo ---------- | |
61 | @point{}The quick brown fox jumped over the lazy dog. | |
62 | ---------- Buffer: foo ---------- | |
63 | @end group | |
64 | ||
65 | @group | |
66 | (search-forward "fox") | |
67 | @result{} 20 | |
68 | ||
69 | ---------- Buffer: foo ---------- | |
70 | The quick brown fox@point{} jumped over the lazy dog. | |
71 | ---------- Buffer: foo ---------- | |
72 | @end group | |
73 | @end example | |
74 | ||
75 | The argument @var{limit} specifies the upper bound to the search. (It | |
76 | must be a position in the current buffer.) No match extending after | |
77 | that position is accepted. If @var{limit} is omitted or @code{nil}, it | |
78 | defaults to the end of the accessible portion of the buffer. | |
79 | ||
80 | @kindex search-failed | |
81 | What happens when the search fails depends on the value of | |
82 | @var{noerror}. If @var{noerror} is @code{nil}, a @code{search-failed} | |
83 | error is signaled. If @var{noerror} is @code{t}, @code{search-forward} | |
84 | returns @code{nil} and does nothing. If @var{noerror} is neither | |
85 | @code{nil} nor @code{t}, then @code{search-forward} moves point to the | |
86 | upper bound and returns @code{nil}. (It would be more consistent now to | |
87 | return the new position of point in that case, but some existing | |
88 | programs may depend on a value of @code{nil}.) | |
89 | ||
90 | The argument @var{noerror} only affects valid searches which fail to | |
91 | find a match. Invalid arguments cause errors regardless of | |
92 | @var{noerror}. | |
93 | ||
94 | If @var{repeat} is supplied (it must be a positive number), then the | |
95 | search is repeated that many times (each time starting at the end of the | |
96 | previous time's match). If these successive searches succeed, the | |
97 | function succeeds, moving point and returning its new value. Otherwise | |
98 | the search fails, with results depending on the value of | |
99 | @var{noerror}, as described above. | |
100 | @end deffn | |
101 | ||
102 | @deffn Command search-backward string &optional limit noerror repeat | |
103 | This function searches backward from point for @var{string}. It is | |
104 | just like @code{search-forward} except that it searches backwards and | |
105 | leaves point at the beginning of the match. | |
106 | @end deffn | |
107 | ||
108 | @deffn Command word-search-forward string &optional limit noerror repeat | |
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109 | This function searches forward from point for a ``word'' match for |
110 | @var{string}. If it finds a match, it sets point to the end of the | |
111 | match found, and returns the new value of point. | |
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112 | |
113 | Word matching regards @var{string} as a sequence of words, disregarding | |
114 | punctuation that separates them. It searches the buffer for the same | |
115 | sequence of words. Each word must be distinct in the buffer (searching | |
116 | for the word @samp{ball} does not match the word @samp{balls}), but the | |
117 | details of punctuation and spacing are ignored (searching for @samp{ball | |
118 | boy} does match @samp{ball. Boy!}). | |
119 | ||
120 | In this example, point is initially at the beginning of the buffer; the | |
121 | search leaves it between the @samp{y} and the @samp{!}. | |
122 | ||
123 | @example | |
124 | @group | |
125 | ---------- Buffer: foo ---------- | |
126 | @point{}He said "Please! Find | |
127 | the ball boy!" | |
128 | ---------- Buffer: foo ---------- | |
129 | @end group | |
130 | ||
131 | @group | |
132 | (word-search-forward "Please find the ball, boy.") | |
133 | @result{} 35 | |
134 | ||
135 | ---------- Buffer: foo ---------- | |
136 | He said "Please! Find | |
137 | the ball boy@point{}!" | |
138 | ---------- Buffer: foo ---------- | |
139 | @end group | |
140 | @end example | |
141 | ||
142 | If @var{limit} is non-@code{nil}, it must be a position in the current | |
143 | buffer; it specifies the upper bound to the search. The match found | |
144 | must not extend after that position. | |
145 | ||
146 | If @var{noerror} is @code{nil}, then @code{word-search-forward} signals | |
147 | an error if the search fails. If @var{noerror} is @code{t}, then it | |
148 | returns @code{nil} instead of signaling an error. If @var{noerror} is | |
149 | neither @code{nil} nor @code{t}, it moves point to @var{limit} (or the | |
150 | end of the accessible portion of the buffer) and returns @code{nil}. | |
151 | ||
152 | If @var{repeat} is non-@code{nil}, then the search is repeated that many | |
153 | times. Point is positioned at the end of the last match. | |
154 | @end deffn | |
155 | ||
fca4ec76 CY |
156 | @deffn Command word-search-forward-lax string &optional limit noerror repeat |
157 | This command is identical to @code{word-search-forward}, except that | |
158 | the end of @code{string} need not match a word boundary unless it ends | |
159 | in whitespace. For instance, searching for @samp{ball boy} matches | |
160 | @samp{ball boyee}, but does not match @samp{aball boy}. | |
161 | @end deffn | |
162 | ||
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163 | @deffn Command word-search-backward string &optional limit noerror repeat |
164 | This function searches backward from point for a word match to | |
165 | @var{string}. This function is just like @code{word-search-forward} | |
166 | except that it searches backward and normally leaves point at the | |
167 | beginning of the match. | |
168 | @end deffn | |
169 | ||
fca4ec76 CY |
170 | @deffn Command word-search-backward-lax string &optional limit noerror repeat |
171 | This command is identical to @code{word-search-backward}, except that | |
172 | the end of @code{string} need not match a word boundary unless it ends | |
173 | in whitespace. | |
174 | @end deffn | |
175 | ||
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176 | @node Searching and Case |
177 | @section Searching and Case | |
178 | @cindex searching and case | |
179 | ||
180 | By default, searches in Emacs ignore the case of the text they are | |
181 | searching through; if you specify searching for @samp{FOO}, then | |
182 | @samp{Foo} or @samp{foo} is also considered a match. This applies to | |
183 | regular expressions, too; thus, @samp{[aB]} would match @samp{a} or | |
184 | @samp{A} or @samp{b} or @samp{B}. | |
185 | ||
186 | If you do not want this feature, set the variable | |
187 | @code{case-fold-search} to @code{nil}. Then all letters must match | |
188 | exactly, including case. This is a buffer-local variable; altering the | |
189 | variable affects only the current buffer. (@xref{Intro to | |
4e3b4528 SM |
190 | Buffer-Local}.) Alternatively, you may change the default value of |
191 | @code{case-fold-search}. | |
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192 | |
193 | Note that the user-level incremental search feature handles case | |
fca4ec76 CY |
194 | distinctions differently. When the search string contains only lower |
195 | case letters, the search ignores case, but when the search string | |
196 | contains one or more upper case letters, the search becomes | |
197 | case-sensitive. But this has nothing to do with the searching | |
198 | functions used in Lisp code. | |
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199 | |
200 | @defopt case-fold-search | |
201 | This buffer-local variable determines whether searches should ignore | |
202 | case. If the variable is @code{nil} they do not ignore case; otherwise | |
203 | they do ignore case. | |
204 | @end defopt | |
205 | ||
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206 | @defopt case-replace |
207 | This variable determines whether the higher level replacement | |
208 | functions should preserve case. If the variable is @code{nil}, that | |
209 | means to use the replacement text verbatim. A non-@code{nil} value | |
210 | means to convert the case of the replacement text according to the | |
211 | text being replaced. | |
212 | ||
213 | This variable is used by passing it as an argument to the function | |
214 | @code{replace-match}. @xref{Replacing Match}. | |
215 | @end defopt | |
216 | ||
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217 | @node Regular Expressions |
218 | @section Regular Expressions | |
219 | @cindex regular expression | |
220 | @cindex regexp | |
221 | ||
fca4ec76 | 222 | A @dfn{regular expression}, or @dfn{regexp} for short, is a pattern that |
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223 | denotes a (possibly infinite) set of strings. Searching for matches for |
224 | a regexp is a very powerful operation. This section explains how to write | |
225 | regexps; the following section says how to search for them. | |
226 | ||
227 | @findex re-builder | |
228 | @cindex regular expressions, developing | |
229 | For convenient interactive development of regular expressions, you | |
230 | can use the @kbd{M-x re-builder} command. It provides a convenient | |
231 | interface for creating regular expressions, by giving immediate visual | |
232 | feedback in a separate buffer. As you edit the regexp, all its | |
233 | matches in the target buffer are highlighted. Each parenthesized | |
234 | sub-expression of the regexp is shown in a distinct face, which makes | |
235 | it easier to verify even very complex regexps. | |
236 | ||
237 | @menu | |
238 | * Syntax of Regexps:: Rules for writing regular expressions. | |
239 | * Regexp Example:: Illustrates regular expression syntax. | |
240 | * Regexp Functions:: Functions for operating on regular expressions. | |
241 | @end menu | |
242 | ||
243 | @node Syntax of Regexps | |
244 | @subsection Syntax of Regular Expressions | |
245 | ||
246 | Regular expressions have a syntax in which a few characters are | |
247 | special constructs and the rest are @dfn{ordinary}. An ordinary | |
248 | character is a simple regular expression that matches that character | |
249 | and nothing else. The special characters are @samp{.}, @samp{*}, | |
250 | @samp{+}, @samp{?}, @samp{[}, @samp{^}, @samp{$}, and @samp{\}; no new | |
251 | special characters will be defined in the future. The character | |
252 | @samp{]} is special if it ends a character alternative (see later). | |
253 | The character @samp{-} is special inside a character alternative. A | |
254 | @samp{[:} and balancing @samp{:]} enclose a character class inside a | |
255 | character alternative. Any other character appearing in a regular | |
256 | expression is ordinary, unless a @samp{\} precedes it. | |
257 | ||
258 | For example, @samp{f} is not a special character, so it is ordinary, and | |
259 | therefore @samp{f} is a regular expression that matches the string | |
260 | @samp{f} and no other string. (It does @emph{not} match the string | |
261 | @samp{fg}, but it does match a @emph{part} of that string.) Likewise, | |
262 | @samp{o} is a regular expression that matches only @samp{o}.@refill | |
263 | ||
264 | Any two regular expressions @var{a} and @var{b} can be concatenated. The | |
265 | result is a regular expression that matches a string if @var{a} matches | |
266 | some amount of the beginning of that string and @var{b} matches the rest of | |
267 | the string.@refill | |
268 | ||
269 | As a simple example, we can concatenate the regular expressions @samp{f} | |
270 | and @samp{o} to get the regular expression @samp{fo}, which matches only | |
271 | the string @samp{fo}. Still trivial. To do something more powerful, you | |
272 | need to use one of the special regular expression constructs. | |
273 | ||
274 | @menu | |
275 | * Regexp Special:: Special characters in regular expressions. | |
276 | * Char Classes:: Character classes used in regular expressions. | |
277 | * Regexp Backslash:: Backslash-sequences in regular expressions. | |
278 | @end menu | |
279 | ||
280 | @node Regexp Special | |
281 | @subsubsection Special Characters in Regular Expressions | |
282 | ||
283 | Here is a list of the characters that are special in a regular | |
284 | expression. | |
285 | ||
286 | @need 800 | |
287 | @table @asis | |
288 | @item @samp{.}@: @r{(Period)} | |
289 | @cindex @samp{.} in regexp | |
290 | is a special character that matches any single character except a newline. | |
291 | Using concatenation, we can make regular expressions like @samp{a.b}, which | |
292 | matches any three-character string that begins with @samp{a} and ends with | |
293 | @samp{b}.@refill | |
294 | ||
295 | @item @samp{*} | |
296 | @cindex @samp{*} in regexp | |
297 | is not a construct by itself; it is a postfix operator that means to | |
298 | match the preceding regular expression repetitively as many times as | |
299 | possible. Thus, @samp{o*} matches any number of @samp{o}s (including no | |
300 | @samp{o}s). | |
301 | ||
302 | @samp{*} always applies to the @emph{smallest} possible preceding | |
303 | expression. Thus, @samp{fo*} has a repeating @samp{o}, not a repeating | |
304 | @samp{fo}. It matches @samp{f}, @samp{fo}, @samp{foo}, and so on. | |
305 | ||
306 | The matcher processes a @samp{*} construct by matching, immediately, as | |
307 | many repetitions as can be found. Then it continues with the rest of | |
308 | the pattern. If that fails, backtracking occurs, discarding some of the | |
309 | matches of the @samp{*}-modified construct in the hope that that will | |
310 | make it possible to match the rest of the pattern. For example, in | |
311 | matching @samp{ca*ar} against the string @samp{caaar}, the @samp{a*} | |
312 | first tries to match all three @samp{a}s; but the rest of the pattern is | |
313 | @samp{ar} and there is only @samp{r} left to match, so this try fails. | |
314 | The next alternative is for @samp{a*} to match only two @samp{a}s. With | |
315 | this choice, the rest of the regexp matches successfully. | |
316 | ||
317 | @strong{Warning:} Nested repetition operators can run for an | |
318 | indefinitely long time, if they lead to ambiguous matching. For | |
319 | example, trying to match the regular expression @samp{\(x+y*\)*a} | |
320 | against the string @samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz} could | |
321 | take hours before it ultimately fails. Emacs must try each way of | |
322 | grouping the @samp{x}s before concluding that none of them can work. | |
323 | Even worse, @samp{\(x*\)*} can match the null string in infinitely | |
324 | many ways, so it causes an infinite loop. To avoid these problems, | |
325 | check nested repetitions carefully, to make sure that they do not | |
326 | cause combinatorial explosions in backtracking. | |
327 | ||
328 | @item @samp{+} | |
329 | @cindex @samp{+} in regexp | |
330 | is a postfix operator, similar to @samp{*} except that it must match | |
331 | the preceding expression at least once. So, for example, @samp{ca+r} | |
332 | matches the strings @samp{car} and @samp{caaaar} but not the string | |
333 | @samp{cr}, whereas @samp{ca*r} matches all three strings. | |
334 | ||
335 | @item @samp{?} | |
336 | @cindex @samp{?} in regexp | |
337 | is a postfix operator, similar to @samp{*} except that it must match the | |
338 | preceding expression either once or not at all. For example, | |
339 | @samp{ca?r} matches @samp{car} or @samp{cr}; nothing else. | |
340 | ||
341 | @item @samp{*?}, @samp{+?}, @samp{??} | |
3645358a | 342 | @cindex non-greedy repetition characters in regexp |
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343 | These are ``non-greedy'' variants of the operators @samp{*}, @samp{+} |
344 | and @samp{?}. Where those operators match the largest possible | |
345 | substring (consistent with matching the entire containing expression), | |
346 | the non-greedy variants match the smallest possible substring | |
347 | (consistent with matching the entire containing expression). | |
348 | ||
349 | For example, the regular expression @samp{c[ad]*a} when applied to the | |
350 | string @samp{cdaaada} matches the whole string; but the regular | |
351 | expression @samp{c[ad]*?a}, applied to that same string, matches just | |
352 | @samp{cda}. (The smallest possible match here for @samp{[ad]*?} that | |
353 | permits the whole expression to match is @samp{d}.) | |
354 | ||
355 | @item @samp{[ @dots{} ]} | |
356 | @cindex character alternative (in regexp) | |
357 | @cindex @samp{[} in regexp | |
358 | @cindex @samp{]} in regexp | |
359 | is a @dfn{character alternative}, which begins with @samp{[} and is | |
360 | terminated by @samp{]}. In the simplest case, the characters between | |
361 | the two brackets are what this character alternative can match. | |
362 | ||
363 | Thus, @samp{[ad]} matches either one @samp{a} or one @samp{d}, and | |
364 | @samp{[ad]*} matches any string composed of just @samp{a}s and @samp{d}s | |
ba3bf1d9 | 365 | (including the empty string). It follows that @samp{c[ad]*r} |
b8d4c8d0 GM |
366 | matches @samp{cr}, @samp{car}, @samp{cdr}, @samp{caddaar}, etc. |
367 | ||
368 | You can also include character ranges in a character alternative, by | |
369 | writing the starting and ending characters with a @samp{-} between them. | |
370 | Thus, @samp{[a-z]} matches any lower-case @acronym{ASCII} letter. | |
371 | Ranges may be intermixed freely with individual characters, as in | |
372 | @samp{[a-z$%.]}, which matches any lower case @acronym{ASCII} letter | |
373 | or @samp{$}, @samp{%} or period. | |
374 | ||
375 | Note that the usual regexp special characters are not special inside a | |
376 | character alternative. A completely different set of characters is | |
377 | special inside character alternatives: @samp{]}, @samp{-} and @samp{^}. | |
378 | ||
379 | To include a @samp{]} in a character alternative, you must make it the | |
380 | first character. For example, @samp{[]a]} matches @samp{]} or @samp{a}. | |
381 | To include a @samp{-}, write @samp{-} as the first or last character of | |
382 | the character alternative, or put it after a range. Thus, @samp{[]-]} | |
383 | matches both @samp{]} and @samp{-}. | |
384 | ||
385 | To include @samp{^} in a character alternative, put it anywhere but at | |
386 | the beginning. | |
387 | ||
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388 | If a range starts with a unibyte character @var{c} and ends with a |
389 | multibyte character @var{c2}, the range is divided into two parts: one | |
390 | is @samp{@var{c}..?\377}, the other is @samp{@var{c1}..@var{c2}}, where | |
391 | @var{c1} is the first character of the charset to which @var{c2} | |
392 | belongs. | |
393 | ||
ba3bf1d9 CY |
394 | A character alternative can also specify named character classes |
395 | (@pxref{Char Classes}). This is a POSIX feature whose syntax is | |
396 | @samp{[:@var{class}:]}. Using a character class is equivalent to | |
397 | mentioning each of the characters in that class; but the latter is not | |
398 | feasible in practice, since some classes include thousands of | |
b8d4c8d0 GM |
399 | different characters. |
400 | ||
401 | @item @samp{[^ @dots{} ]} | |
402 | @cindex @samp{^} in regexp | |
403 | @samp{[^} begins a @dfn{complemented character alternative}. This | |
404 | matches any character except the ones specified. Thus, | |
405 | @samp{[^a-z0-9A-Z]} matches all characters @emph{except} letters and | |
406 | digits. | |
407 | ||
408 | @samp{^} is not special in a character alternative unless it is the first | |
409 | character. The character following the @samp{^} is treated as if it | |
410 | were first (in other words, @samp{-} and @samp{]} are not special there). | |
411 | ||
412 | A complemented character alternative can match a newline, unless newline is | |
413 | mentioned as one of the characters not to match. This is in contrast to | |
414 | the handling of regexps in programs such as @code{grep}. | |
415 | ||
ba3bf1d9 CY |
416 | You can specify named character classes, just like in character |
417 | alternatives. For instance, @samp{[^[:ascii:]]} matches any | |
418 | non-@acronym{ASCII} character. @xref{Char Classes}. | |
419 | ||
b8d4c8d0 GM |
420 | @item @samp{^} |
421 | @cindex beginning of line in regexp | |
422 | When matching a buffer, @samp{^} matches the empty string, but only at the | |
423 | beginning of a line in the text being matched (or the beginning of the | |
424 | accessible portion of the buffer). Otherwise it fails to match | |
425 | anything. Thus, @samp{^foo} matches a @samp{foo} that occurs at the | |
426 | beginning of a line. | |
427 | ||
428 | When matching a string instead of a buffer, @samp{^} matches at the | |
429 | beginning of the string or after a newline character. | |
430 | ||
431 | For historical compatibility reasons, @samp{^} can be used only at the | |
432 | beginning of the regular expression, or after @samp{\(}, @samp{\(?:} | |
433 | or @samp{\|}. | |
434 | ||
435 | @item @samp{$} | |
436 | @cindex @samp{$} in regexp | |
437 | @cindex end of line in regexp | |
438 | is similar to @samp{^} but matches only at the end of a line (or the | |
439 | end of the accessible portion of the buffer). Thus, @samp{x+$} | |
440 | matches a string of one @samp{x} or more at the end of a line. | |
441 | ||
442 | When matching a string instead of a buffer, @samp{$} matches at the end | |
443 | of the string or before a newline character. | |
444 | ||
445 | For historical compatibility reasons, @samp{$} can be used only at the | |
446 | end of the regular expression, or before @samp{\)} or @samp{\|}. | |
447 | ||
448 | @item @samp{\} | |
449 | @cindex @samp{\} in regexp | |
450 | has two functions: it quotes the special characters (including | |
451 | @samp{\}), and it introduces additional special constructs. | |
452 | ||
453 | Because @samp{\} quotes special characters, @samp{\$} is a regular | |
454 | expression that matches only @samp{$}, and @samp{\[} is a regular | |
455 | expression that matches only @samp{[}, and so on. | |
456 | ||
457 | Note that @samp{\} also has special meaning in the read syntax of Lisp | |
458 | strings (@pxref{String Type}), and must be quoted with @samp{\}. For | |
459 | example, the regular expression that matches the @samp{\} character is | |
460 | @samp{\\}. To write a Lisp string that contains the characters | |
461 | @samp{\\}, Lisp syntax requires you to quote each @samp{\} with another | |
462 | @samp{\}. Therefore, the read syntax for a regular expression matching | |
463 | @samp{\} is @code{"\\\\"}.@refill | |
464 | @end table | |
465 | ||
466 | @strong{Please note:} For historical compatibility, special characters | |
467 | are treated as ordinary ones if they are in contexts where their special | |
468 | meanings make no sense. For example, @samp{*foo} treats @samp{*} as | |
469 | ordinary since there is no preceding expression on which the @samp{*} | |
470 | can act. It is poor practice to depend on this behavior; quote the | |
471 | special character anyway, regardless of where it appears.@refill | |
472 | ||
473 | As a @samp{\} is not special inside a character alternative, it can | |
474 | never remove the special meaning of @samp{-} or @samp{]}. So you | |
475 | should not quote these characters when they have no special meaning | |
476 | either. This would not clarify anything, since backslashes can | |
477 | legitimately precede these characters where they @emph{have} special | |
478 | meaning, as in @samp{[^\]} (@code{"[^\\]"} for Lisp string syntax), | |
479 | which matches any single character except a backslash. | |
480 | ||
481 | In practice, most @samp{]} that occur in regular expressions close a | |
482 | character alternative and hence are special. However, occasionally a | |
483 | regular expression may try to match a complex pattern of literal | |
484 | @samp{[} and @samp{]}. In such situations, it sometimes may be | |
485 | necessary to carefully parse the regexp from the start to determine | |
486 | which square brackets enclose a character alternative. For example, | |
487 | @samp{[^][]]} consists of the complemented character alternative | |
488 | @samp{[^][]} (which matches any single character that is not a square | |
489 | bracket), followed by a literal @samp{]}. | |
490 | ||
491 | The exact rules are that at the beginning of a regexp, @samp{[} is | |
492 | special and @samp{]} not. This lasts until the first unquoted | |
493 | @samp{[}, after which we are in a character alternative; @samp{[} is | |
494 | no longer special (except when it starts a character class) but @samp{]} | |
495 | is special, unless it immediately follows the special @samp{[} or that | |
496 | @samp{[} followed by a @samp{^}. This lasts until the next special | |
497 | @samp{]} that does not end a character class. This ends the character | |
498 | alternative and restores the ordinary syntax of regular expressions; | |
499 | an unquoted @samp{[} is special again and a @samp{]} not. | |
500 | ||
501 | @node Char Classes | |
502 | @subsubsection Character Classes | |
503 | @cindex character classes in regexp | |
504 | ||
505 | Here is a table of the classes you can use in a character alternative, | |
506 | and what they mean: | |
507 | ||
508 | @table @samp | |
509 | @item [:ascii:] | |
510 | This matches any @acronym{ASCII} character (codes 0--127). | |
511 | @item [:alnum:] | |
512 | This matches any letter or digit. (At present, for multibyte | |
513 | characters, it matches anything that has word syntax.) | |
514 | @item [:alpha:] | |
515 | This matches any letter. (At present, for multibyte characters, it | |
516 | matches anything that has word syntax.) | |
517 | @item [:blank:] | |
518 | This matches space and tab only. | |
519 | @item [:cntrl:] | |
520 | This matches any @acronym{ASCII} control character. | |
521 | @item [:digit:] | |
522 | This matches @samp{0} through @samp{9}. Thus, @samp{[-+[:digit:]]} | |
523 | matches any digit, as well as @samp{+} and @samp{-}. | |
524 | @item [:graph:] | |
525 | This matches graphic characters---everything except @acronym{ASCII} control | |
526 | characters, space, and the delete character. | |
527 | @item [:lower:] | |
4359a806 CY |
528 | This matches any lower-case letter, as determined by the current case |
529 | table (@pxref{Case Tables}). If @code{case-fold-search} is | |
530 | non-@code{nil}, this also matches any upper-case letter. | |
b8d4c8d0 GM |
531 | @item [:multibyte:] |
532 | This matches any multibyte character (@pxref{Text Representations}). | |
533 | @item [:nonascii:] | |
534 | This matches any non-@acronym{ASCII} character. | |
535 | @item [:print:] | |
536 | This matches printing characters---everything except @acronym{ASCII} control | |
537 | characters and the delete character. | |
538 | @item [:punct:] | |
539 | This matches any punctuation character. (At present, for multibyte | |
540 | characters, it matches anything that has non-word syntax.) | |
541 | @item [:space:] | |
542 | This matches any character that has whitespace syntax | |
543 | (@pxref{Syntax Class Table}). | |
544 | @item [:unibyte:] | |
545 | This matches any unibyte character (@pxref{Text Representations}). | |
546 | @item [:upper:] | |
4359a806 CY |
547 | This matches any upper-case letter, as determined by the current case |
548 | table (@pxref{Case Tables}). If @code{case-fold-search} is | |
549 | non-@code{nil}, this also matches any lower-case letter. | |
b8d4c8d0 GM |
550 | @item [:word:] |
551 | This matches any character that has word syntax (@pxref{Syntax Class | |
552 | Table}). | |
553 | @item [:xdigit:] | |
554 | This matches the hexadecimal digits: @samp{0} through @samp{9}, @samp{a} | |
555 | through @samp{f} and @samp{A} through @samp{F}. | |
556 | @end table | |
557 | ||
558 | @node Regexp Backslash | |
559 | @subsubsection Backslash Constructs in Regular Expressions | |
560 | ||
561 | For the most part, @samp{\} followed by any character matches only | |
562 | that character. However, there are several exceptions: certain | |
563 | two-character sequences starting with @samp{\} that have special | |
564 | meanings. (The character after the @samp{\} in such a sequence is | |
565 | always ordinary when used on its own.) Here is a table of the special | |
566 | @samp{\} constructs. | |
567 | ||
568 | @table @samp | |
569 | @item \| | |
570 | @cindex @samp{|} in regexp | |
571 | @cindex regexp alternative | |
572 | specifies an alternative. | |
573 | Two regular expressions @var{a} and @var{b} with @samp{\|} in | |
574 | between form an expression that matches anything that either @var{a} or | |
575 | @var{b} matches.@refill | |
576 | ||
577 | Thus, @samp{foo\|bar} matches either @samp{foo} or @samp{bar} | |
578 | but no other string.@refill | |
579 | ||
580 | @samp{\|} applies to the largest possible surrounding expressions. Only a | |
581 | surrounding @samp{\( @dots{} \)} grouping can limit the grouping power of | |
582 | @samp{\|}.@refill | |
583 | ||
584 | If you need full backtracking capability to handle multiple uses of | |
585 | @samp{\|}, use the POSIX regular expression functions (@pxref{POSIX | |
586 | Regexps}). | |
587 | ||
588 | @item \@{@var{m}\@} | |
589 | is a postfix operator that repeats the previous pattern exactly @var{m} | |
590 | times. Thus, @samp{x\@{5\@}} matches the string @samp{xxxxx} | |
591 | and nothing else. @samp{c[ad]\@{3\@}r} matches string such as | |
592 | @samp{caaar}, @samp{cdddr}, @samp{cadar}, and so on. | |
593 | ||
594 | @item \@{@var{m},@var{n}\@} | |
595 | is a more general postfix operator that specifies repetition with a | |
596 | minimum of @var{m} repeats and a maximum of @var{n} repeats. If @var{m} | |
597 | is omitted, the minimum is 0; if @var{n} is omitted, there is no | |
598 | maximum. | |
599 | ||
600 | For example, @samp{c[ad]\@{1,2\@}r} matches the strings @samp{car}, | |
601 | @samp{cdr}, @samp{caar}, @samp{cadr}, @samp{cdar}, and @samp{cddr}, and | |
602 | nothing else.@* | |
d24880de GM |
603 | @samp{\@{0,1\@}} or @samp{\@{,1\@}} is equivalent to @samp{?}.@* |
604 | @samp{\@{0,\@}} or @samp{\@{,\@}} is equivalent to @samp{*}.@* | |
b8d4c8d0 GM |
605 | @samp{\@{1,\@}} is equivalent to @samp{+}. |
606 | ||
607 | @item \( @dots{} \) | |
608 | @cindex @samp{(} in regexp | |
609 | @cindex @samp{)} in regexp | |
610 | @cindex regexp grouping | |
611 | is a grouping construct that serves three purposes: | |
612 | ||
613 | @enumerate | |
614 | @item | |
615 | To enclose a set of @samp{\|} alternatives for other operations. Thus, | |
616 | the regular expression @samp{\(foo\|bar\)x} matches either @samp{foox} | |
617 | or @samp{barx}. | |
618 | ||
619 | @item | |
620 | To enclose a complicated expression for the postfix operators @samp{*}, | |
621 | @samp{+} and @samp{?} to operate on. Thus, @samp{ba\(na\)*} matches | |
622 | @samp{ba}, @samp{bana}, @samp{banana}, @samp{bananana}, etc., with any | |
623 | number (zero or more) of @samp{na} strings. | |
624 | ||
625 | @item | |
626 | To record a matched substring for future reference with | |
627 | @samp{\@var{digit}} (see below). | |
628 | @end enumerate | |
629 | ||
630 | This last application is not a consequence of the idea of a | |
631 | parenthetical grouping; it is a separate feature that was assigned as a | |
632 | second meaning to the same @samp{\( @dots{} \)} construct because, in | |
633 | practice, there was usually no conflict between the two meanings. But | |
634 | occasionally there is a conflict, and that led to the introduction of | |
635 | shy groups. | |
636 | ||
637 | @item \(?: @dots{} \) | |
80d7cdca CY |
638 | @cindex shy groups |
639 | @cindex non-capturing group | |
640 | @cindex unnumbered group | |
47f24290 | 641 | @cindex @samp{(?:} in regexp |
b8d4c8d0 GM |
642 | is the @dfn{shy group} construct. A shy group serves the first two |
643 | purposes of an ordinary group (controlling the nesting of other | |
644 | operators), but it does not get a number, so you cannot refer back to | |
80d7cdca CY |
645 | its value with @samp{\@var{digit}}. Shy groups are particularly |
646 | useful for mechanically-constructed regular expressions, because they | |
647 | can be added automatically without altering the numbering of ordinary, | |
648 | non-shy groups. | |
b8d4c8d0 | 649 | |
80d7cdca CY |
650 | Shy groups are also called @dfn{non-capturing} or @dfn{unnumbered |
651 | groups}. | |
b8d4c8d0 GM |
652 | |
653 | @item \(?@var{num}: @dots{} \) | |
654 | is the @dfn{explicitly numbered group} construct. Normal groups get | |
655 | their number implicitly, based on their position, which can be | |
656 | inconvenient. This construct allows you to force a particular group | |
657 | number. There is no particular restriction on the numbering, | |
658 | e.g.@: you can have several groups with the same number in which case | |
659 | the last one to match (i.e.@: the rightmost match) will win. | |
660 | Implicitly numbered groups always get the smallest integer larger than | |
661 | the one of any previous group. | |
662 | ||
663 | @item \@var{digit} | |
664 | matches the same text that matched the @var{digit}th occurrence of a | |
665 | grouping (@samp{\( @dots{} \)}) construct. | |
666 | ||
667 | In other words, after the end of a group, the matcher remembers the | |
668 | beginning and end of the text matched by that group. Later on in the | |
669 | regular expression you can use @samp{\} followed by @var{digit} to | |
670 | match that same text, whatever it may have been. | |
671 | ||
672 | The strings matching the first nine grouping constructs appearing in | |
673 | the entire regular expression passed to a search or matching function | |
674 | are assigned numbers 1 through 9 in the order that the open | |
675 | parentheses appear in the regular expression. So you can use | |
676 | @samp{\1} through @samp{\9} to refer to the text matched by the | |
677 | corresponding grouping constructs. | |
678 | ||
679 | For example, @samp{\(.*\)\1} matches any newline-free string that is | |
680 | composed of two identical halves. The @samp{\(.*\)} matches the first | |
681 | half, which may be anything, but the @samp{\1} that follows must match | |
682 | the same exact text. | |
683 | ||
684 | If a @samp{\( @dots{} \)} construct matches more than once (which can | |
685 | happen, for instance, if it is followed by @samp{*}), only the last | |
686 | match is recorded. | |
687 | ||
688 | If a particular grouping construct in the regular expression was never | |
689 | matched---for instance, if it appears inside of an alternative that | |
690 | wasn't used, or inside of a repetition that repeated zero times---then | |
691 | the corresponding @samp{\@var{digit}} construct never matches | |
748c30f4 | 692 | anything. To use an artificial example, @samp{\(foo\(b*\)\|lose\)\2} |
b8d4c8d0 GM |
693 | cannot match @samp{lose}: the second alternative inside the larger |
694 | group matches it, but then @samp{\2} is undefined and can't match | |
695 | anything. But it can match @samp{foobb}, because the first | |
696 | alternative matches @samp{foob} and @samp{\2} matches @samp{b}. | |
697 | ||
698 | @item \w | |
699 | @cindex @samp{\w} in regexp | |
700 | matches any word-constituent character. The editor syntax table | |
701 | determines which characters these are. @xref{Syntax Tables}. | |
702 | ||
703 | @item \W | |
704 | @cindex @samp{\W} in regexp | |
705 | matches any character that is not a word constituent. | |
706 | ||
707 | @item \s@var{code} | |
708 | @cindex @samp{\s} in regexp | |
709 | matches any character whose syntax is @var{code}. Here @var{code} is a | |
710 | character that represents a syntax code: thus, @samp{w} for word | |
711 | constituent, @samp{-} for whitespace, @samp{(} for open parenthesis, | |
712 | etc. To represent whitespace syntax, use either @samp{-} or a space | |
713 | character. @xref{Syntax Class Table}, for a list of syntax codes and | |
714 | the characters that stand for them. | |
715 | ||
716 | @item \S@var{code} | |
717 | @cindex @samp{\S} in regexp | |
718 | matches any character whose syntax is not @var{code}. | |
719 | ||
720 | @item \c@var{c} | |
721 | matches any character whose category is @var{c}. Here @var{c} is a | |
722 | character that represents a category: thus, @samp{c} for Chinese | |
723 | characters or @samp{g} for Greek characters in the standard category | |
724 | table. | |
725 | ||
726 | @item \C@var{c} | |
727 | matches any character whose category is not @var{c}. | |
728 | @end table | |
729 | ||
730 | The following regular expression constructs match the empty string---that is, | |
731 | they don't use up any characters---but whether they match depends on the | |
732 | context. For all, the beginning and end of the accessible portion of | |
733 | the buffer are treated as if they were the actual beginning and end of | |
734 | the buffer. | |
735 | ||
736 | @table @samp | |
737 | @item \` | |
738 | @cindex @samp{\`} in regexp | |
739 | matches the empty string, but only at the beginning | |
740 | of the buffer or string being matched against. | |
741 | ||
742 | @item \' | |
743 | @cindex @samp{\'} in regexp | |
744 | matches the empty string, but only at the end of | |
745 | the buffer or string being matched against. | |
746 | ||
747 | @item \= | |
748 | @cindex @samp{\=} in regexp | |
749 | matches the empty string, but only at point. | |
750 | (This construct is not defined when matching against a string.) | |
751 | ||
752 | @item \b | |
753 | @cindex @samp{\b} in regexp | |
754 | matches the empty string, but only at the beginning or | |
755 | end of a word. Thus, @samp{\bfoo\b} matches any occurrence of | |
756 | @samp{foo} as a separate word. @samp{\bballs?\b} matches | |
757 | @samp{ball} or @samp{balls} as a separate word.@refill | |
758 | ||
759 | @samp{\b} matches at the beginning or end of the buffer (or string) | |
760 | regardless of what text appears next to it. | |
761 | ||
762 | @item \B | |
763 | @cindex @samp{\B} in regexp | |
764 | matches the empty string, but @emph{not} at the beginning or | |
765 | end of a word, nor at the beginning or end of the buffer (or string). | |
766 | ||
767 | @item \< | |
768 | @cindex @samp{\<} in regexp | |
769 | matches the empty string, but only at the beginning of a word. | |
770 | @samp{\<} matches at the beginning of the buffer (or string) only if a | |
771 | word-constituent character follows. | |
772 | ||
773 | @item \> | |
774 | @cindex @samp{\>} in regexp | |
775 | matches the empty string, but only at the end of a word. @samp{\>} | |
776 | matches at the end of the buffer (or string) only if the contents end | |
777 | with a word-constituent character. | |
778 | ||
779 | @item \_< | |
780 | @cindex @samp{\_<} in regexp | |
781 | matches the empty string, but only at the beginning of a symbol. A | |
782 | symbol is a sequence of one or more word or symbol constituent | |
783 | characters. @samp{\_<} matches at the beginning of the buffer (or | |
784 | string) only if a symbol-constituent character follows. | |
785 | ||
786 | @item \_> | |
787 | @cindex @samp{\_>} in regexp | |
788 | matches the empty string, but only at the end of a symbol. @samp{\_>} | |
789 | matches at the end of the buffer (or string) only if the contents end | |
790 | with a symbol-constituent character. | |
791 | @end table | |
792 | ||
793 | @kindex invalid-regexp | |
794 | Not every string is a valid regular expression. For example, a string | |
795 | that ends inside a character alternative without terminating @samp{]} | |
796 | is invalid, and so is a string that ends with a single @samp{\}. If | |
797 | an invalid regular expression is passed to any of the search functions, | |
798 | an @code{invalid-regexp} error is signaled. | |
799 | ||
800 | @node Regexp Example | |
801 | @comment node-name, next, previous, up | |
802 | @subsection Complex Regexp Example | |
803 | ||
804 | Here is a complicated regexp which was formerly used by Emacs to | |
805 | recognize the end of a sentence together with any whitespace that | |
806 | follows. (Nowadays Emacs uses a similar but more complex default | |
807 | regexp constructed by the function @code{sentence-end}. | |
808 | @xref{Standard Regexps}.) | |
809 | ||
810 | First, we show the regexp as a string in Lisp syntax to distinguish | |
811 | spaces from tab characters. The string constant begins and ends with a | |
812 | double-quote. @samp{\"} stands for a double-quote as part of the | |
813 | string, @samp{\\} for a backslash as part of the string, @samp{\t} for a | |
814 | tab and @samp{\n} for a newline. | |
815 | ||
816 | @example | |
817 | "[.?!][]\"')@}]*\\($\\| $\\|\t\\|@ @ \\)[ \t\n]*" | |
818 | @end example | |
819 | ||
820 | @noindent | |
821 | In contrast, if you evaluate this string, you will see the following: | |
822 | ||
823 | @example | |
824 | @group | |
825 | "[.?!][]\"')@}]*\\($\\| $\\|\t\\|@ @ \\)[ \t\n]*" | |
826 | @result{} "[.?!][]\"')@}]*\\($\\| $\\| \\|@ @ \\)[ | |
827 | ]*" | |
828 | @end group | |
829 | @end example | |
830 | ||
831 | @noindent | |
832 | In this output, tab and newline appear as themselves. | |
833 | ||
834 | This regular expression contains four parts in succession and can be | |
835 | deciphered as follows: | |
836 | ||
837 | @table @code | |
838 | @item [.?!] | |
839 | The first part of the pattern is a character alternative that matches | |
840 | any one of three characters: period, question mark, and exclamation | |
841 | mark. The match must begin with one of these three characters. (This | |
842 | is one point where the new default regexp used by Emacs differs from | |
843 | the old. The new value also allows some non-@acronym{ASCII} | |
844 | characters that end a sentence without any following whitespace.) | |
845 | ||
846 | @item []\"')@}]* | |
847 | The second part of the pattern matches any closing braces and quotation | |
848 | marks, zero or more of them, that may follow the period, question mark | |
849 | or exclamation mark. The @code{\"} is Lisp syntax for a double-quote in | |
850 | a string. The @samp{*} at the end indicates that the immediately | |
851 | preceding regular expression (a character alternative, in this case) may be | |
852 | repeated zero or more times. | |
853 | ||
854 | @item \\($\\|@ $\\|\t\\|@ @ \\) | |
855 | The third part of the pattern matches the whitespace that follows the | |
856 | end of a sentence: the end of a line (optionally with a space), or a | |
857 | tab, or two spaces. The double backslashes mark the parentheses and | |
858 | vertical bars as regular expression syntax; the parentheses delimit a | |
859 | group and the vertical bars separate alternatives. The dollar sign is | |
860 | used to match the end of a line. | |
861 | ||
862 | @item [ \t\n]* | |
863 | Finally, the last part of the pattern matches any additional whitespace | |
864 | beyond the minimum needed to end a sentence. | |
865 | @end table | |
866 | ||
867 | @node Regexp Functions | |
868 | @subsection Regular Expression Functions | |
869 | ||
870 | These functions operate on regular expressions. | |
871 | ||
872 | @defun regexp-quote string | |
873 | This function returns a regular expression whose only exact match is | |
874 | @var{string}. Using this regular expression in @code{looking-at} will | |
875 | succeed only if the next characters in the buffer are @var{string}; | |
876 | using it in a search function will succeed if the text being searched | |
877 | contains @var{string}. | |
878 | ||
879 | This allows you to request an exact string match or search when calling | |
880 | a function that wants a regular expression. | |
881 | ||
882 | @example | |
883 | @group | |
884 | (regexp-quote "^The cat$") | |
885 | @result{} "\\^The cat\\$" | |
886 | @end group | |
887 | @end example | |
888 | ||
889 | One use of @code{regexp-quote} is to combine an exact string match with | |
890 | context described as a regular expression. For example, this searches | |
891 | for the string that is the value of @var{string}, surrounded by | |
892 | whitespace: | |
893 | ||
894 | @example | |
895 | @group | |
896 | (re-search-forward | |
897 | (concat "\\s-" (regexp-quote string) "\\s-")) | |
898 | @end group | |
899 | @end example | |
900 | @end defun | |
901 | ||
902 | @defun regexp-opt strings &optional paren | |
903 | This function returns an efficient regular expression that will match | |
904 | any of the strings in the list @var{strings}. This is useful when you | |
905 | need to make matching or searching as fast as possible---for example, | |
906 | for Font Lock mode. | |
907 | ||
908 | If the optional argument @var{paren} is non-@code{nil}, then the | |
909 | returned regular expression is always enclosed by at least one | |
910 | parentheses-grouping construct. If @var{paren} is @code{words}, then | |
07ff7702 MB |
911 | that construct is additionally surrounded by @samp{\<} and @samp{\>}; |
912 | alternatively, if @var{paren} is @code{symbols}, then that construct | |
913 | is additionally surrounded by @samp{\_<} and @samp{\_>} | |
914 | (@code{symbols} is often appropriate when matching | |
915 | programming-language keywords and the like). | |
b8d4c8d0 GM |
916 | |
917 | This simplified definition of @code{regexp-opt} produces a | |
918 | regular expression which is equivalent to the actual value | |
919 | (but not as efficient): | |
920 | ||
921 | @example | |
922 | (defun regexp-opt (strings paren) | |
923 | (let ((open-paren (if paren "\\(" "")) | |
924 | (close-paren (if paren "\\)" ""))) | |
925 | (concat open-paren | |
926 | (mapconcat 'regexp-quote strings "\\|") | |
927 | close-paren))) | |
928 | @end example | |
929 | @end defun | |
930 | ||
931 | @defun regexp-opt-depth regexp | |
932 | This function returns the total number of grouping constructs | |
80d7cdca CY |
933 | (parenthesized expressions) in @var{regexp}. This does not include |
934 | shy groups (@pxref{Regexp Backslash}). | |
b8d4c8d0 GM |
935 | @end defun |
936 | ||
937 | @node Regexp Search | |
938 | @section Regular Expression Searching | |
939 | @cindex regular expression searching | |
940 | @cindex regexp searching | |
941 | @cindex searching for regexp | |
942 | ||
943 | In GNU Emacs, you can search for the next match for a regular | |
944 | expression either incrementally or not. For incremental search | |
945 | commands, see @ref{Regexp Search, , Regular Expression Search, emacs, | |
946 | The GNU Emacs Manual}. Here we describe only the search functions | |
947 | useful in programs. The principal one is @code{re-search-forward}. | |
948 | ||
949 | These search functions convert the regular expression to multibyte if | |
950 | the buffer is multibyte; they convert the regular expression to unibyte | |
951 | if the buffer is unibyte. @xref{Text Representations}. | |
952 | ||
953 | @deffn Command re-search-forward regexp &optional limit noerror repeat | |
954 | This function searches forward in the current buffer for a string of | |
955 | text that is matched by the regular expression @var{regexp}. The | |
956 | function skips over any amount of text that is not matched by | |
957 | @var{regexp}, and leaves point at the end of the first match found. | |
958 | It returns the new value of point. | |
959 | ||
960 | If @var{limit} is non-@code{nil}, it must be a position in the current | |
961 | buffer. It specifies the upper bound to the search. No match | |
962 | extending after that position is accepted. | |
963 | ||
964 | If @var{repeat} is supplied, it must be a positive number; the search | |
965 | is repeated that many times; each repetition starts at the end of the | |
966 | previous match. If all these successive searches succeed, the search | |
967 | succeeds, moving point and returning its new value. Otherwise the | |
968 | search fails. What @code{re-search-forward} does when the search | |
969 | fails depends on the value of @var{noerror}: | |
970 | ||
971 | @table @asis | |
972 | @item @code{nil} | |
973 | Signal a @code{search-failed} error. | |
974 | @item @code{t} | |
975 | Do nothing and return @code{nil}. | |
976 | @item anything else | |
977 | Move point to @var{limit} (or the end of the accessible portion of the | |
978 | buffer) and return @code{nil}. | |
979 | @end table | |
980 | ||
981 | In the following example, point is initially before the @samp{T}. | |
982 | Evaluating the search call moves point to the end of that line (between | |
983 | the @samp{t} of @samp{hat} and the newline). | |
984 | ||
985 | @example | |
986 | @group | |
987 | ---------- Buffer: foo ---------- | |
988 | I read "@point{}The cat in the hat | |
989 | comes back" twice. | |
990 | ---------- Buffer: foo ---------- | |
991 | @end group | |
992 | ||
993 | @group | |
994 | (re-search-forward "[a-z]+" nil t 5) | |
995 | @result{} 27 | |
996 | ||
997 | ---------- Buffer: foo ---------- | |
998 | I read "The cat in the hat@point{} | |
999 | comes back" twice. | |
1000 | ---------- Buffer: foo ---------- | |
1001 | @end group | |
1002 | @end example | |
1003 | @end deffn | |
1004 | ||
1005 | @deffn Command re-search-backward regexp &optional limit noerror repeat | |
1006 | This function searches backward in the current buffer for a string of | |
1007 | text that is matched by the regular expression @var{regexp}, leaving | |
1008 | point at the beginning of the first text found. | |
1009 | ||
1010 | This function is analogous to @code{re-search-forward}, but they are not | |
1011 | simple mirror images. @code{re-search-forward} finds the match whose | |
1012 | beginning is as close as possible to the starting point. If | |
1013 | @code{re-search-backward} were a perfect mirror image, it would find the | |
1014 | match whose end is as close as possible. However, in fact it finds the | |
1015 | match whose beginning is as close as possible (and yet ends before the | |
1016 | starting point). The reason for this is that matching a regular | |
1017 | expression at a given spot always works from beginning to end, and | |
1018 | starts at a specified beginning position. | |
1019 | ||
1020 | A true mirror-image of @code{re-search-forward} would require a special | |
1021 | feature for matching regular expressions from end to beginning. It's | |
1022 | not worth the trouble of implementing that. | |
1023 | @end deffn | |
1024 | ||
1025 | @defun string-match regexp string &optional start | |
1026 | This function returns the index of the start of the first match for | |
1027 | the regular expression @var{regexp} in @var{string}, or @code{nil} if | |
1028 | there is no match. If @var{start} is non-@code{nil}, the search starts | |
1029 | at that index in @var{string}. | |
1030 | ||
1031 | For example, | |
1032 | ||
1033 | @example | |
1034 | @group | |
1035 | (string-match | |
1036 | "quick" "The quick brown fox jumped quickly.") | |
1037 | @result{} 4 | |
1038 | @end group | |
1039 | @group | |
1040 | (string-match | |
1041 | "quick" "The quick brown fox jumped quickly." 8) | |
1042 | @result{} 27 | |
1043 | @end group | |
1044 | @end example | |
1045 | ||
1046 | @noindent | |
1047 | The index of the first character of the | |
1048 | string is 0, the index of the second character is 1, and so on. | |
1049 | ||
1050 | After this function returns, the index of the first character beyond | |
1051 | the match is available as @code{(match-end 0)}. @xref{Match Data}. | |
1052 | ||
1053 | @example | |
1054 | @group | |
1055 | (string-match | |
1056 | "quick" "The quick brown fox jumped quickly." 8) | |
1057 | @result{} 27 | |
1058 | @end group | |
1059 | ||
1060 | @group | |
1061 | (match-end 0) | |
1062 | @result{} 32 | |
1063 | @end group | |
1064 | @end example | |
1065 | @end defun | |
1066 | ||
3645358a | 1067 | @defun string-match-p regexp string &optional start |
4433fa91 EZ |
1068 | This predicate function does what @code{string-match} does, but it |
1069 | avoids modifying the match data. | |
3645358a EZ |
1070 | @end defun |
1071 | ||
b8d4c8d0 GM |
1072 | @defun looking-at regexp |
1073 | This function determines whether the text in the current buffer directly | |
1074 | following point matches the regular expression @var{regexp}. ``Directly | |
1075 | following'' means precisely that: the search is ``anchored'' and it can | |
1076 | succeed only starting with the first character following point. The | |
1077 | result is @code{t} if so, @code{nil} otherwise. | |
1078 | ||
1079 | This function does not move point, but it updates the match data, which | |
1080 | you can access using @code{match-beginning} and @code{match-end}. | |
3645358a EZ |
1081 | @xref{Match Data}. If you need to test for a match without modifying |
1082 | the match data, use @code{looking-at-p}, described below. | |
b8d4c8d0 GM |
1083 | |
1084 | In this example, point is located directly before the @samp{T}. If it | |
1085 | were anywhere else, the result would be @code{nil}. | |
1086 | ||
1087 | @example | |
1088 | @group | |
1089 | ---------- Buffer: foo ---------- | |
1090 | I read "@point{}The cat in the hat | |
1091 | comes back" twice. | |
1092 | ---------- Buffer: foo ---------- | |
1093 | ||
1094 | (looking-at "The cat in the hat$") | |
1095 | @result{} t | |
1096 | @end group | |
1097 | @end example | |
1098 | @end defun | |
1099 | ||
1899a5d0 | 1100 | @defun looking-back regexp &optional limit greedy |
b8d4c8d0 GM |
1101 | This function returns @code{t} if @var{regexp} matches text before |
1102 | point, ending at point, and @code{nil} otherwise. | |
1103 | ||
1104 | Because regular expression matching works only going forward, this is | |
1105 | implemented by searching backwards from point for a match that ends at | |
1106 | point. That can be quite slow if it has to search a long distance. | |
1107 | You can bound the time required by specifying @var{limit}, which says | |
1108 | not to search before @var{limit}. In this case, the match that is | |
1109 | found must begin at or after @var{limit}. | |
1110 | ||
1899a5d0 CY |
1111 | If @var{greedy} is non-@code{nil}, this function extends the match |
1112 | backwards as far as possible, stopping when a single additional | |
1113 | previous character cannot be part of a match for regexp. When the | |
d60a8ab2 | 1114 | match is extended, its starting position is allowed to occur before |
1899a5d0 CY |
1115 | @var{limit}. |
1116 | ||
b8d4c8d0 GM |
1117 | @example |
1118 | @group | |
1119 | ---------- Buffer: foo ---------- | |
1120 | I read "@point{}The cat in the hat | |
1121 | comes back" twice. | |
1122 | ---------- Buffer: foo ---------- | |
1123 | ||
1124 | (looking-back "read \"" 3) | |
1125 | @result{} t | |
1126 | (looking-back "read \"" 4) | |
1127 | @result{} nil | |
1128 | @end group | |
1129 | @end example | |
1130 | @end defun | |
1131 | ||
3645358a EZ |
1132 | @defun looking-at-p regexp |
1133 | This predicate function works like @code{looking-at}, but without | |
1134 | updating the match data. | |
1135 | @end defun | |
1136 | ||
b8d4c8d0 GM |
1137 | @defvar search-spaces-regexp |
1138 | If this variable is non-@code{nil}, it should be a regular expression | |
1139 | that says how to search for whitespace. In that case, any group of | |
1140 | spaces in a regular expression being searched for stands for use of | |
1141 | this regular expression. However, spaces inside of constructs such as | |
1142 | @samp{[@dots{}]} and @samp{*}, @samp{+}, @samp{?} are not affected by | |
1143 | @code{search-spaces-regexp}. | |
1144 | ||
1145 | Since this variable affects all regular expression search and match | |
1146 | constructs, you should bind it temporarily for as small as possible | |
1147 | a part of the code. | |
1148 | @end defvar | |
1149 | ||
1150 | @node POSIX Regexps | |
1151 | @section POSIX Regular Expression Searching | |
1152 | ||
1153 | The usual regular expression functions do backtracking when necessary | |
1154 | to handle the @samp{\|} and repetition constructs, but they continue | |
1155 | this only until they find @emph{some} match. Then they succeed and | |
1156 | report the first match found. | |
1157 | ||
1158 | This section describes alternative search functions which perform the | |
1159 | full backtracking specified by the POSIX standard for regular expression | |
1160 | matching. They continue backtracking until they have tried all | |
1161 | possibilities and found all matches, so they can report the longest | |
1162 | match, as required by POSIX. This is much slower, so use these | |
1163 | functions only when you really need the longest match. | |
1164 | ||
1165 | The POSIX search and match functions do not properly support the | |
3645358a EZ |
1166 | non-greedy repetition operators (@pxref{Regexp Special, non-greedy}). |
1167 | This is because POSIX backtracking conflicts with the semantics of | |
1168 | non-greedy repetition. | |
b8d4c8d0 | 1169 | |
106e6894 | 1170 | @deffn Command posix-search-forward regexp &optional limit noerror repeat |
b8d4c8d0 GM |
1171 | This is like @code{re-search-forward} except that it performs the full |
1172 | backtracking specified by the POSIX standard for regular expression | |
1173 | matching. | |
106e6894 | 1174 | @end deffn |
b8d4c8d0 | 1175 | |
106e6894 | 1176 | @deffn Command posix-search-backward regexp &optional limit noerror repeat |
b8d4c8d0 GM |
1177 | This is like @code{re-search-backward} except that it performs the full |
1178 | backtracking specified by the POSIX standard for regular expression | |
1179 | matching. | |
106e6894 | 1180 | @end deffn |
b8d4c8d0 GM |
1181 | |
1182 | @defun posix-looking-at regexp | |
1183 | This is like @code{looking-at} except that it performs the full | |
1184 | backtracking specified by the POSIX standard for regular expression | |
1185 | matching. | |
1186 | @end defun | |
1187 | ||
1188 | @defun posix-string-match regexp string &optional start | |
1189 | This is like @code{string-match} except that it performs the full | |
1190 | backtracking specified by the POSIX standard for regular expression | |
1191 | matching. | |
1192 | @end defun | |
1193 | ||
1194 | @node Match Data | |
1195 | @section The Match Data | |
1196 | @cindex match data | |
1197 | ||
1198 | Emacs keeps track of the start and end positions of the segments of | |
1199 | text found during a search; this is called the @dfn{match data}. | |
1200 | Thanks to the match data, you can search for a complex pattern, such | |
1201 | as a date in a mail message, and then extract parts of the match under | |
1202 | control of the pattern. | |
1203 | ||
1204 | Because the match data normally describe the most recent search only, | |
1205 | you must be careful not to do another search inadvertently between the | |
1206 | search you wish to refer back to and the use of the match data. If you | |
1207 | can't avoid another intervening search, you must save and restore the | |
1208 | match data around it, to prevent it from being overwritten. | |
1209 | ||
1210 | @menu | |
d24880de | 1211 | * Replacing Match:: Replacing a substring that was matched. |
b8d4c8d0 | 1212 | * Simple Match Data:: Accessing single items of match data, |
d24880de | 1213 | such as where a particular subexpression started. |
b8d4c8d0 GM |
1214 | * Entire Match Data:: Accessing the entire match data at once, as a list. |
1215 | * Saving Match Data:: Saving and restoring the match data. | |
1216 | @end menu | |
1217 | ||
1218 | @node Replacing Match | |
1219 | @subsection Replacing the Text that Matched | |
1220 | @cindex replace matched text | |
1221 | ||
1222 | This function replaces all or part of the text matched by the last | |
1223 | search. It works by means of the match data. | |
1224 | ||
1225 | @cindex case in replacements | |
1226 | @defun replace-match replacement &optional fixedcase literal string subexp | |
1227 | This function replaces the text in the buffer (or in @var{string}) that | |
1228 | was matched by the last search. It replaces that text with | |
1229 | @var{replacement}. | |
1230 | ||
1231 | If you did the last search in a buffer, you should specify @code{nil} | |
1232 | for @var{string} and make sure that the current buffer when you call | |
1233 | @code{replace-match} is the one in which you did the searching or | |
1234 | matching. Then @code{replace-match} does the replacement by editing | |
1235 | the buffer; it leaves point at the end of the replacement text, and | |
1236 | returns @code{t}. | |
1237 | ||
1238 | If you did the search in a string, pass the same string as @var{string}. | |
1239 | Then @code{replace-match} does the replacement by constructing and | |
1240 | returning a new string. | |
1241 | ||
1242 | If @var{fixedcase} is non-@code{nil}, then @code{replace-match} uses | |
1243 | the replacement text without case conversion; otherwise, it converts | |
1244 | the replacement text depending upon the capitalization of the text to | |
1245 | be replaced. If the original text is all upper case, this converts | |
1246 | the replacement text to upper case. If all words of the original text | |
1247 | are capitalized, this capitalizes all the words of the replacement | |
1248 | text. If all the words are one-letter and they are all upper case, | |
1249 | they are treated as capitalized words rather than all-upper-case | |
1250 | words. | |
1251 | ||
1252 | If @var{literal} is non-@code{nil}, then @var{replacement} is inserted | |
1253 | exactly as it is, the only alterations being case changes as needed. | |
1254 | If it is @code{nil} (the default), then the character @samp{\} is treated | |
1255 | specially. If a @samp{\} appears in @var{replacement}, then it must be | |
1256 | part of one of the following sequences: | |
1257 | ||
1258 | @table @asis | |
1259 | @item @samp{\&} | |
1260 | @cindex @samp{&} in replacement | |
1261 | @samp{\&} stands for the entire text being replaced. | |
1262 | ||
1263 | @item @samp{\@var{n}} | |
1264 | @cindex @samp{\@var{n}} in replacement | |
1265 | @samp{\@var{n}}, where @var{n} is a digit, stands for the text that | |
1266 | matched the @var{n}th subexpression in the original regexp. | |
1267 | Subexpressions are those expressions grouped inside @samp{\(@dots{}\)}. | |
1268 | If the @var{n}th subexpression never matched, an empty string is substituted. | |
1269 | ||
1270 | @item @samp{\\} | |
1271 | @cindex @samp{\} in replacement | |
1272 | @samp{\\} stands for a single @samp{\} in the replacement text. | |
1273 | @end table | |
1274 | ||
1275 | These substitutions occur after case conversion, if any, | |
1276 | so the strings they substitute are never case-converted. | |
1277 | ||
1278 | If @var{subexp} is non-@code{nil}, that says to replace just | |
1279 | subexpression number @var{subexp} of the regexp that was matched, not | |
1280 | the entire match. For example, after matching @samp{foo \(ba*r\)}, | |
1281 | calling @code{replace-match} with 1 as @var{subexp} means to replace | |
1282 | just the text that matched @samp{\(ba*r\)}. | |
1283 | @end defun | |
1284 | ||
fe284805 JL |
1285 | @defun match-substitute-replacement replacement &optional fixedcase literal string subexp |
1286 | This function returns the text that would be inserted into the buffer | |
1287 | by @code{replace-match}, but without modifying the buffer. It is | |
1288 | useful if you want to present the user with actual replacement result, | |
1289 | with constructs like @samp{\@var{n}} or @samp{\&} substituted with | |
1290 | matched groups. Arguments @var{replacement} and optional | |
1291 | @var{fixedcase}, @var{literal}, @var{string} and @var{subexp} have the | |
1292 | same meaning as for @code{replace-match}. | |
1293 | @end defun | |
1294 | ||
b8d4c8d0 GM |
1295 | @node Simple Match Data |
1296 | @subsection Simple Match Data Access | |
1297 | ||
1298 | This section explains how to use the match data to find out what was | |
1299 | matched by the last search or match operation, if it succeeded. | |
1300 | ||
1301 | You can ask about the entire matching text, or about a particular | |
1302 | parenthetical subexpression of a regular expression. The @var{count} | |
1303 | argument in the functions below specifies which. If @var{count} is | |
1304 | zero, you are asking about the entire match. If @var{count} is | |
1305 | positive, it specifies which subexpression you want. | |
1306 | ||
1307 | Recall that the subexpressions of a regular expression are those | |
1308 | expressions grouped with escaped parentheses, @samp{\(@dots{}\)}. The | |
1309 | @var{count}th subexpression is found by counting occurrences of | |
1310 | @samp{\(} from the beginning of the whole regular expression. The first | |
1311 | subexpression is numbered 1, the second 2, and so on. Only regular | |
1312 | expressions can have subexpressions---after a simple string search, the | |
1313 | only information available is about the entire match. | |
1314 | ||
1315 | Every successful search sets the match data. Therefore, you should | |
1316 | query the match data immediately after searching, before calling any | |
1317 | other function that might perform another search. Alternatively, you | |
1318 | may save and restore the match data (@pxref{Saving Match Data}) around | |
1319 | the call to functions that could perform another search. | |
1320 | ||
1321 | A search which fails may or may not alter the match data. In the | |
1322 | past, a failing search did not do this, but we may change it in the | |
1323 | future. So don't try to rely on the value of the match data after | |
1324 | a failing search. | |
1325 | ||
1326 | @defun match-string count &optional in-string | |
1327 | This function returns, as a string, the text matched in the last search | |
1328 | or match operation. It returns the entire text if @var{count} is zero, | |
1329 | or just the portion corresponding to the @var{count}th parenthetical | |
1330 | subexpression, if @var{count} is positive. | |
1331 | ||
1332 | If the last such operation was done against a string with | |
1333 | @code{string-match}, then you should pass the same string as the | |
1334 | argument @var{in-string}. After a buffer search or match, | |
1335 | you should omit @var{in-string} or pass @code{nil} for it; but you | |
1336 | should make sure that the current buffer when you call | |
1337 | @code{match-string} is the one in which you did the searching or | |
1338 | matching. | |
1339 | ||
1340 | The value is @code{nil} if @var{count} is out of range, or for a | |
1341 | subexpression inside a @samp{\|} alternative that wasn't used or a | |
1342 | repetition that repeated zero times. | |
1343 | @end defun | |
1344 | ||
1345 | @defun match-string-no-properties count &optional in-string | |
1346 | This function is like @code{match-string} except that the result | |
1347 | has no text properties. | |
1348 | @end defun | |
1349 | ||
1350 | @defun match-beginning count | |
1351 | This function returns the position of the start of text matched by the | |
1352 | last regular expression searched for, or a subexpression of it. | |
1353 | ||
1354 | If @var{count} is zero, then the value is the position of the start of | |
1355 | the entire match. Otherwise, @var{count} specifies a subexpression in | |
1356 | the regular expression, and the value of the function is the starting | |
1357 | position of the match for that subexpression. | |
1358 | ||
1359 | The value is @code{nil} for a subexpression inside a @samp{\|} | |
1360 | alternative that wasn't used or a repetition that repeated zero times. | |
1361 | @end defun | |
1362 | ||
1363 | @defun match-end count | |
1364 | This function is like @code{match-beginning} except that it returns the | |
1365 | position of the end of the match, rather than the position of the | |
1366 | beginning. | |
1367 | @end defun | |
1368 | ||
1369 | Here is an example of using the match data, with a comment showing the | |
1370 | positions within the text: | |
1371 | ||
1372 | @example | |
1373 | @group | |
1374 | (string-match "\\(qu\\)\\(ick\\)" | |
1375 | "The quick fox jumped quickly.") | |
1376 | ;0123456789 | |
1377 | @result{} 4 | |
1378 | @end group | |
1379 | ||
1380 | @group | |
1381 | (match-string 0 "The quick fox jumped quickly.") | |
1382 | @result{} "quick" | |
1383 | (match-string 1 "The quick fox jumped quickly.") | |
1384 | @result{} "qu" | |
1385 | (match-string 2 "The quick fox jumped quickly.") | |
1386 | @result{} "ick" | |
1387 | @end group | |
1388 | ||
1389 | @group | |
1390 | (match-beginning 1) ; @r{The beginning of the match} | |
1391 | @result{} 4 ; @r{with @samp{qu} is at index 4.} | |
1392 | @end group | |
1393 | ||
1394 | @group | |
1395 | (match-beginning 2) ; @r{The beginning of the match} | |
1396 | @result{} 6 ; @r{with @samp{ick} is at index 6.} | |
1397 | @end group | |
1398 | ||
1399 | @group | |
1400 | (match-end 1) ; @r{The end of the match} | |
1401 | @result{} 6 ; @r{with @samp{qu} is at index 6.} | |
1402 | ||
1403 | (match-end 2) ; @r{The end of the match} | |
1404 | @result{} 9 ; @r{with @samp{ick} is at index 9.} | |
1405 | @end group | |
1406 | @end example | |
1407 | ||
1408 | Here is another example. Point is initially located at the beginning | |
1409 | of the line. Searching moves point to between the space and the word | |
1410 | @samp{in}. The beginning of the entire match is at the 9th character of | |
1411 | the buffer (@samp{T}), and the beginning of the match for the first | |
1412 | subexpression is at the 13th character (@samp{c}). | |
1413 | ||
1414 | @example | |
1415 | @group | |
1416 | (list | |
1417 | (re-search-forward "The \\(cat \\)") | |
1418 | (match-beginning 0) | |
1419 | (match-beginning 1)) | |
1899a5d0 | 1420 | @result{} (17 9 13) |
b8d4c8d0 GM |
1421 | @end group |
1422 | ||
1423 | @group | |
1424 | ---------- Buffer: foo ---------- | |
1425 | I read "The cat @point{}in the hat comes back" twice. | |
1426 | ^ ^ | |
1427 | 9 13 | |
1428 | ---------- Buffer: foo ---------- | |
1429 | @end group | |
1430 | @end example | |
1431 | ||
1432 | @noindent | |
1433 | (In this case, the index returned is a buffer position; the first | |
1434 | character of the buffer counts as 1.) | |
1435 | ||
1436 | @node Entire Match Data | |
1437 | @subsection Accessing the Entire Match Data | |
1438 | ||
1439 | The functions @code{match-data} and @code{set-match-data} read or | |
1440 | write the entire match data, all at once. | |
1441 | ||
1442 | @defun match-data &optional integers reuse reseat | |
1443 | This function returns a list of positions (markers or integers) that | |
1444 | record all the information on what text the last search matched. | |
1445 | Element zero is the position of the beginning of the match for the | |
1446 | whole expression; element one is the position of the end of the match | |
1447 | for the expression. The next two elements are the positions of the | |
1448 | beginning and end of the match for the first subexpression, and so on. | |
1449 | In general, element | |
1450 | @ifnottex | |
1451 | number 2@var{n} | |
1452 | @end ifnottex | |
1453 | @tex | |
1454 | number {\mathsurround=0pt $2n$} | |
1455 | @end tex | |
1456 | corresponds to @code{(match-beginning @var{n})}; and | |
1457 | element | |
1458 | @ifnottex | |
1459 | number 2@var{n} + 1 | |
1460 | @end ifnottex | |
1461 | @tex | |
1462 | number {\mathsurround=0pt $2n+1$} | |
1463 | @end tex | |
1464 | corresponds to @code{(match-end @var{n})}. | |
1465 | ||
1466 | Normally all the elements are markers or @code{nil}, but if | |
1467 | @var{integers} is non-@code{nil}, that means to use integers instead | |
1468 | of markers. (In that case, the buffer itself is appended as an | |
1469 | additional element at the end of the list, to facilitate complete | |
1470 | restoration of the match data.) If the last match was done on a | |
1471 | string with @code{string-match}, then integers are always used, | |
1472 | since markers can't point into a string. | |
1473 | ||
1474 | If @var{reuse} is non-@code{nil}, it should be a list. In that case, | |
1475 | @code{match-data} stores the match data in @var{reuse}. That is, | |
1476 | @var{reuse} is destructively modified. @var{reuse} does not need to | |
1477 | have the right length. If it is not long enough to contain the match | |
1478 | data, it is extended. If it is too long, the length of @var{reuse} | |
1479 | stays the same, but the elements that were not used are set to | |
1480 | @code{nil}. The purpose of this feature is to reduce the need for | |
1481 | garbage collection. | |
1482 | ||
1483 | If @var{reseat} is non-@code{nil}, all markers on the @var{reuse} list | |
1484 | are reseated to point to nowhere. | |
1485 | ||
1486 | As always, there must be no possibility of intervening searches between | |
1487 | the call to a search function and the call to @code{match-data} that is | |
1488 | intended to access the match data for that search. | |
1489 | ||
1490 | @example | |
1491 | @group | |
1492 | (match-data) | |
1493 | @result{} (#<marker at 9 in foo> | |
1494 | #<marker at 17 in foo> | |
1495 | #<marker at 13 in foo> | |
1496 | #<marker at 17 in foo>) | |
1497 | @end group | |
1498 | @end example | |
1499 | @end defun | |
1500 | ||
1501 | @defun set-match-data match-list &optional reseat | |
1502 | This function sets the match data from the elements of @var{match-list}, | |
1503 | which should be a list that was the value of a previous call to | |
1504 | @code{match-data}. (More precisely, anything that has the same format | |
1505 | will work.) | |
1506 | ||
1507 | If @var{match-list} refers to a buffer that doesn't exist, you don't get | |
1508 | an error; that sets the match data in a meaningless but harmless way. | |
1509 | ||
1510 | If @var{reseat} is non-@code{nil}, all markers on the @var{match-list} list | |
1511 | are reseated to point to nowhere. | |
1512 | ||
1513 | @findex store-match-data | |
1514 | @code{store-match-data} is a semi-obsolete alias for @code{set-match-data}. | |
1515 | @end defun | |
1516 | ||
1517 | @node Saving Match Data | |
1518 | @subsection Saving and Restoring the Match Data | |
1519 | ||
1520 | When you call a function that may do a search, you may need to save | |
1521 | and restore the match data around that call, if you want to preserve the | |
1522 | match data from an earlier search for later use. Here is an example | |
1523 | that shows the problem that arises if you fail to save the match data: | |
1524 | ||
1525 | @example | |
1526 | @group | |
1527 | (re-search-forward "The \\(cat \\)") | |
1528 | @result{} 48 | |
1529 | (foo) ; @r{Perhaps @code{foo} does} | |
1530 | ; @r{more searching.} | |
1531 | (match-end 0) | |
1532 | @result{} 61 ; @r{Unexpected result---not 48!} | |
1533 | @end group | |
1534 | @end example | |
1535 | ||
1536 | You can save and restore the match data with @code{save-match-data}: | |
1537 | ||
1538 | @defmac save-match-data body@dots{} | |
1539 | This macro executes @var{body}, saving and restoring the match | |
1540 | data around it. The return value is the value of the last form in | |
1541 | @var{body}. | |
1542 | @end defmac | |
1543 | ||
1544 | You could use @code{set-match-data} together with @code{match-data} to | |
1545 | imitate the effect of the special form @code{save-match-data}. Here is | |
1546 | how: | |
1547 | ||
1548 | @example | |
1549 | @group | |
1550 | (let ((data (match-data))) | |
1551 | (unwind-protect | |
1552 | @dots{} ; @r{Ok to change the original match data.} | |
1553 | (set-match-data data))) | |
1554 | @end group | |
1555 | @end example | |
1556 | ||
1557 | Emacs automatically saves and restores the match data when it runs | |
1558 | process filter functions (@pxref{Filter Functions}) and process | |
1559 | sentinels (@pxref{Sentinels}). | |
1560 | ||
1561 | @ignore | |
1562 | Here is a function which restores the match data provided the buffer | |
1563 | associated with it still exists. | |
1564 | ||
1565 | @smallexample | |
1566 | @group | |
1567 | (defun restore-match-data (data) | |
1568 | @c It is incorrect to split the first line of a doc string. | |
1569 | @c If there's a problem here, it should be solved in some other way. | |
1570 | "Restore the match data DATA unless the buffer is missing." | |
1571 | (catch 'foo | |
1572 | (let ((d data)) | |
1573 | @end group | |
1574 | (while d | |
1575 | (and (car d) | |
1576 | (null (marker-buffer (car d))) | |
1577 | @group | |
1578 | ;; @file{match-data} @r{buffer is deleted.} | |
1579 | (throw 'foo nil)) | |
1580 | (setq d (cdr d))) | |
1581 | (set-match-data data)))) | |
1582 | @end group | |
1583 | @end smallexample | |
1584 | @end ignore | |
1585 | ||
1586 | @node Search and Replace | |
1587 | @section Search and Replace | |
1588 | @cindex replacement after search | |
1589 | @cindex searching and replacing | |
1590 | ||
1591 | If you want to find all matches for a regexp in part of the buffer, | |
1592 | and replace them, the best way is to write an explicit loop using | |
1593 | @code{re-search-forward} and @code{replace-match}, like this: | |
1594 | ||
1595 | @example | |
1596 | (while (re-search-forward "foo[ \t]+bar" nil t) | |
1597 | (replace-match "foobar")) | |
1598 | @end example | |
1599 | ||
1600 | @noindent | |
1601 | @xref{Replacing Match,, Replacing the Text that Matched}, for a | |
1602 | description of @code{replace-match}. | |
1603 | ||
1604 | However, replacing matches in a string is more complex, especially | |
1605 | if you want to do it efficiently. So Emacs provides a function to do | |
1606 | this. | |
1607 | ||
1608 | @defun replace-regexp-in-string regexp rep string &optional fixedcase literal subexp start | |
1609 | This function copies @var{string} and searches it for matches for | |
1610 | @var{regexp}, and replaces them with @var{rep}. It returns the | |
1611 | modified copy. If @var{start} is non-@code{nil}, the search for | |
1612 | matches starts at that index in @var{string}, so matches starting | |
1613 | before that index are not changed. | |
1614 | ||
1615 | This function uses @code{replace-match} to do the replacement, and it | |
1616 | passes the optional arguments @var{fixedcase}, @var{literal} and | |
1617 | @var{subexp} along to @code{replace-match}. | |
1618 | ||
1619 | Instead of a string, @var{rep} can be a function. In that case, | |
1620 | @code{replace-regexp-in-string} calls @var{rep} for each match, | |
1621 | passing the text of the match as its sole argument. It collects the | |
1622 | value @var{rep} returns and passes that to @code{replace-match} as the | |
1623 | replacement string. The match-data at this point are the result | |
1624 | of matching @var{regexp} against a substring of @var{string}. | |
1625 | @end defun | |
1626 | ||
1627 | If you want to write a command along the lines of @code{query-replace}, | |
1628 | you can use @code{perform-replace} to do the work. | |
1629 | ||
1630 | @defun perform-replace from-string replacements query-flag regexp-flag delimited-flag &optional repeat-count map start end | |
1631 | This function is the guts of @code{query-replace} and related | |
1632 | commands. It searches for occurrences of @var{from-string} in the | |
1633 | text between positions @var{start} and @var{end} and replaces some or | |
1634 | all of them. If @var{start} is @code{nil} (or omitted), point is used | |
1635 | instead, and the end of the buffer's accessible portion is used for | |
1636 | @var{end}. | |
1637 | ||
1638 | If @var{query-flag} is @code{nil}, it replaces all | |
1639 | occurrences; otherwise, it asks the user what to do about each one. | |
1640 | ||
1641 | If @var{regexp-flag} is non-@code{nil}, then @var{from-string} is | |
1642 | considered a regular expression; otherwise, it must match literally. If | |
1643 | @var{delimited-flag} is non-@code{nil}, then only replacements | |
1644 | surrounded by word boundaries are considered. | |
1645 | ||
1646 | The argument @var{replacements} specifies what to replace occurrences | |
1647 | with. If it is a string, that string is used. It can also be a list of | |
1648 | strings, to be used in cyclic order. | |
1649 | ||
80120f13 EZ |
1650 | If @var{replacements} is a cons cell, @w{@code{(@var{function} |
1651 | . @var{data})}}, this means to call @var{function} after each match to | |
b8d4c8d0 GM |
1652 | get the replacement text. This function is called with two arguments: |
1653 | @var{data}, and the number of replacements already made. | |
1654 | ||
1655 | If @var{repeat-count} is non-@code{nil}, it should be an integer. Then | |
1656 | it specifies how many times to use each of the strings in the | |
1657 | @var{replacements} list before advancing cyclically to the next one. | |
1658 | ||
1659 | If @var{from-string} contains upper-case letters, then | |
1660 | @code{perform-replace} binds @code{case-fold-search} to @code{nil}, and | |
1661 | it uses the @code{replacements} without altering the case of them. | |
1662 | ||
1663 | Normally, the keymap @code{query-replace-map} defines the possible | |
1664 | user responses for queries. The argument @var{map}, if | |
1665 | non-@code{nil}, specifies a keymap to use instead of | |
1666 | @code{query-replace-map}. | |
80120f13 EZ |
1667 | |
1668 | This function uses one of two functions to search for the next | |
1669 | occurrence of @var{from-string}. These functions are specified by the | |
1670 | values of two variables: @code{replace-re-search-function} and | |
1671 | @code{replace-search-function}. The former is called when the | |
1672 | argument @var{regexp-flag} is non-@code{nil}, the latter when it is | |
1673 | @code{nil}. | |
b8d4c8d0 GM |
1674 | @end defun |
1675 | ||
1676 | @defvar query-replace-map | |
1677 | This variable holds a special keymap that defines the valid user | |
1678 | responses for @code{perform-replace} and the commands that use it, as | |
1679 | well as @code{y-or-n-p} and @code{map-y-or-n-p}. This map is unusual | |
1680 | in two ways: | |
1681 | ||
1682 | @itemize @bullet | |
1683 | @item | |
1684 | The ``key bindings'' are not commands, just symbols that are meaningful | |
1685 | to the functions that use this map. | |
1686 | ||
1687 | @item | |
1688 | Prefix keys are not supported; each key binding must be for a | |
1689 | single-event key sequence. This is because the functions don't use | |
1690 | @code{read-key-sequence} to get the input; instead, they read a single | |
1691 | event and look it up ``by hand.'' | |
1692 | @end itemize | |
1693 | @end defvar | |
1694 | ||
1695 | Here are the meaningful ``bindings'' for @code{query-replace-map}. | |
1696 | Several of them are meaningful only for @code{query-replace} and | |
1697 | friends. | |
1698 | ||
1699 | @table @code | |
1700 | @item act | |
1701 | Do take the action being considered---in other words, ``yes.'' | |
1702 | ||
1703 | @item skip | |
1704 | Do not take action for this question---in other words, ``no.'' | |
1705 | ||
1706 | @item exit | |
1707 | Answer this question ``no,'' and give up on the entire series of | |
1708 | questions, assuming that the answers will be ``no.'' | |
1709 | ||
1710 | @item act-and-exit | |
1711 | Answer this question ``yes,'' and give up on the entire series of | |
1712 | questions, assuming that subsequent answers will be ``no.'' | |
1713 | ||
1714 | @item act-and-show | |
1715 | Answer this question ``yes,'' but show the results---don't advance yet | |
1716 | to the next question. | |
1717 | ||
1718 | @item automatic | |
1719 | Answer this question and all subsequent questions in the series with | |
1720 | ``yes,'' without further user interaction. | |
1721 | ||
1722 | @item backup | |
1723 | Move back to the previous place that a question was asked about. | |
1724 | ||
1725 | @item edit | |
1726 | Enter a recursive edit to deal with this question---instead of any | |
1727 | other action that would normally be taken. | |
1728 | ||
1729 | @item delete-and-edit | |
1730 | Delete the text being considered, then enter a recursive edit to replace | |
1731 | it. | |
1732 | ||
1733 | @item recenter | |
1734 | Redisplay and center the window, then ask the same question again. | |
1735 | ||
1736 | @item quit | |
1737 | Perform a quit right away. Only @code{y-or-n-p} and related functions | |
1738 | use this answer. | |
1739 | ||
1740 | @item help | |
1741 | Display some help, then ask again. | |
1742 | @end table | |
1743 | ||
2c0b8144 EZ |
1744 | @defvar multi-query-replace-map |
1745 | This variable holds a keymap that extends @code{query-replace-map} by | |
1746 | providing additional keybindings that are useful in multi-buffer | |
1747 | replacements. | |
1748 | @end defvar | |
1749 | ||
80120f13 EZ |
1750 | @defvar replace-search-function |
1751 | This variable specifies a function that @code{perform-replace} calls | |
1752 | to search for the next string to replace. Its default value is | |
1753 | @code{search-forward}. Any other value should name a function of 3 | |
1754 | arguments: the first 3 arguments of @code{search-forward} | |
1755 | (@pxref{String Search}). | |
1756 | @end defvar | |
1757 | ||
1758 | @defvar replace-re-search-function | |
1759 | This variable specifies a function that @code{perform-replace} calls | |
1760 | to search for the next regexp to replace. Its default value is | |
1761 | @code{re-search-forward}. Any other value should name a function of 3 | |
1762 | arguments: the first 3 arguments of @code{re-search-forward} | |
1763 | (@pxref{Regexp Search}). | |
1764 | @end defvar | |
1765 | ||
b8d4c8d0 GM |
1766 | @node Standard Regexps |
1767 | @section Standard Regular Expressions Used in Editing | |
1768 | @cindex regexps used standardly in editing | |
1769 | @cindex standard regexps used in editing | |
1770 | ||
1771 | This section describes some variables that hold regular expressions | |
1772 | used for certain purposes in editing: | |
1773 | ||
01f17ae2 | 1774 | @defopt page-delimiter |
b8d4c8d0 GM |
1775 | This is the regular expression describing line-beginnings that separate |
1776 | pages. The default value is @code{"^\014"} (i.e., @code{"^^L"} or | |
1777 | @code{"^\C-l"}); this matches a line that starts with a formfeed | |
1778 | character. | |
01f17ae2 | 1779 | @end defopt |
b8d4c8d0 GM |
1780 | |
1781 | The following two regular expressions should @emph{not} assume the | |
1782 | match always starts at the beginning of a line; they should not use | |
1783 | @samp{^} to anchor the match. Most often, the paragraph commands do | |
1784 | check for a match only at the beginning of a line, which means that | |
1785 | @samp{^} would be superfluous. When there is a nonzero left margin, | |
1786 | they accept matches that start after the left margin. In that case, a | |
1787 | @samp{^} would be incorrect. However, a @samp{^} is harmless in modes | |
1788 | where a left margin is never used. | |
1789 | ||
01f17ae2 | 1790 | @defopt paragraph-separate |
b8d4c8d0 GM |
1791 | This is the regular expression for recognizing the beginning of a line |
1792 | that separates paragraphs. (If you change this, you may have to | |
1793 | change @code{paragraph-start} also.) The default value is | |
1794 | @w{@code{"[@ \t\f]*$"}}, which matches a line that consists entirely of | |
1795 | spaces, tabs, and form feeds (after its left margin). | |
01f17ae2 | 1796 | @end defopt |
b8d4c8d0 | 1797 | |
01f17ae2 | 1798 | @defopt paragraph-start |
b8d4c8d0 GM |
1799 | This is the regular expression for recognizing the beginning of a line |
1800 | that starts @emph{or} separates paragraphs. The default value is | |
1801 | @w{@code{"\f\\|[ \t]*$"}}, which matches a line containing only | |
1802 | whitespace or starting with a form feed (after its left margin). | |
01f17ae2 | 1803 | @end defopt |
b8d4c8d0 | 1804 | |
01f17ae2 | 1805 | @defopt sentence-end |
b8d4c8d0 GM |
1806 | If non-@code{nil}, the value should be a regular expression describing |
1807 | the end of a sentence, including the whitespace following the | |
1808 | sentence. (All paragraph boundaries also end sentences, regardless.) | |
1809 | ||
1810 | If the value is @code{nil}, the default, then the function | |
1811 | @code{sentence-end} has to construct the regexp. That is why you | |
1812 | should always call the function @code{sentence-end} to obtain the | |
1813 | regexp to be used to recognize the end of a sentence. | |
01f17ae2 | 1814 | @end defopt |
b8d4c8d0 GM |
1815 | |
1816 | @defun sentence-end | |
1817 | This function returns the value of the variable @code{sentence-end}, | |
1818 | if non-@code{nil}. Otherwise it returns a default value based on the | |
1819 | values of the variables @code{sentence-end-double-space} | |
1820 | (@pxref{Definition of sentence-end-double-space}), | |
1821 | @code{sentence-end-without-period} and | |
1822 | @code{sentence-end-without-space}. | |
1823 | @end defun |