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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
651f374c TTN |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2002, 2003, |
4 | @c 2004, 2005 Free Software Foundation, Inc. | |
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5 | @c See the file elisp.texi for copying conditions. |
6 | @setfilename ../info/searching | |
f9f59935 | 7 | @node Searching and Matching, Syntax Tables, Non-ASCII Characters, Top |
7015aca4 RS |
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 | * Regular Expressions:: Describing classes of strings. | |
20 | * Regexp Search:: Searching for a match for a regexp. | |
22697dac | 21 | * POSIX Regexps:: Searching POSIX-style for the longest match. |
7015aca4 | 22 | * Search and Replace:: Internals of @code{query-replace}. |
2a233172 RS |
23 | * Match Data:: Finding out which part of the text matched, |
24 | after a string or regexp search. | |
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25 | * Searching and Case:: Case-independent or case-significant searching. |
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}. | |
31 | ||
32 | @node String Search | |
33 | @section Searching for Strings | |
34 | @cindex string search | |
35 | ||
36 | These are the primitive functions for searching through the text in a | |
37 | buffer. They are meant for use in programs, but you may call them | |
8241495d RS |
38 | interactively. If you do so, they prompt for the search string; the |
39 | arguments @var{limit} and @var{noerror} are @code{nil}, and @var{repeat} | |
40 | is 1. | |
7015aca4 | 41 | |
f9f59935 RS |
42 | These search functions convert the search string to multibyte if the |
43 | buffer is multibyte; they convert the search string to unibyte if the | |
44 | buffer is unibyte. @xref{Text Representations}. | |
45 | ||
7015aca4 | 46 | @deffn Command search-forward string &optional limit noerror repeat |
f9f59935 | 47 | This function searches forward from point for an exact match for |
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48 | @var{string}. If successful, it sets point to the end of the occurrence |
49 | found, and returns the new value of point. If no match is found, the | |
50 | value and side effects depend on @var{noerror} (see below). | |
51 | @c Emacs 19 feature | |
52 | ||
f9f59935 | 53 | In the following example, point is initially at the beginning of the |
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54 | line. Then @code{(search-forward "fox")} moves point after the last |
55 | letter of @samp{fox}: | |
56 | ||
57 | @example | |
58 | @group | |
59 | ---------- Buffer: foo ---------- | |
60 | @point{}The quick brown fox jumped over the lazy dog. | |
61 | ---------- Buffer: foo ---------- | |
62 | @end group | |
63 | ||
64 | @group | |
65 | (search-forward "fox") | |
66 | @result{} 20 | |
67 | ||
68 | ---------- Buffer: foo ---------- | |
69 | The quick brown fox@point{} jumped over the lazy dog. | |
70 | ---------- Buffer: foo ---------- | |
71 | @end group | |
72 | @end example | |
73 | ||
f9f59935 | 74 | The argument @var{limit} specifies the upper bound to the search. (It |
7015aca4 RS |
75 | must be a position in the current buffer.) No match extending after |
76 | that position is accepted. If @var{limit} is omitted or @code{nil}, it | |
77 | defaults to the end of the accessible portion of the buffer. | |
78 | ||
79 | @kindex search-failed | |
f9f59935 | 80 | What happens when the search fails depends on the value of |
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81 | @var{noerror}. If @var{noerror} is @code{nil}, a @code{search-failed} |
82 | error is signaled. If @var{noerror} is @code{t}, @code{search-forward} | |
83 | returns @code{nil} and does nothing. If @var{noerror} is neither | |
84 | @code{nil} nor @code{t}, then @code{search-forward} moves point to the | |
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85 | upper bound and returns @code{nil}. (It would be more consistent now to |
86 | return the new position of point in that case, but some existing | |
87 | programs may depend on a value of @code{nil}.) | |
7015aca4 | 88 | |
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89 | If @var{repeat} is supplied (it must be a positive number), then the |
90 | search is repeated that many times (each time starting at the end of the | |
91 | previous time's match). If these successive searches succeed, the | |
92 | function succeeds, moving point and returning its new value. Otherwise | |
bcb6b6b8 LT |
93 | the search fails, with results depending on the value of |
94 | @var{noerror}, as described above. | |
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95 | @end deffn |
96 | ||
97 | @deffn Command search-backward string &optional limit noerror repeat | |
98 | This function searches backward from point for @var{string}. It is | |
99 | just like @code{search-forward} except that it searches backwards and | |
100 | leaves point at the beginning of the match. | |
101 | @end deffn | |
102 | ||
103 | @deffn Command word-search-forward string &optional limit noerror repeat | |
104 | @cindex word search | |
105 | This function searches forward from point for a ``word'' match for | |
106 | @var{string}. If it finds a match, it sets point to the end of the | |
107 | match found, and returns the new value of point. | |
108 | @c Emacs 19 feature | |
109 | ||
110 | Word matching regards @var{string} as a sequence of words, disregarding | |
111 | punctuation that separates them. It searches the buffer for the same | |
112 | sequence of words. Each word must be distinct in the buffer (searching | |
113 | for the word @samp{ball} does not match the word @samp{balls}), but the | |
114 | details of punctuation and spacing are ignored (searching for @samp{ball | |
115 | boy} does match @samp{ball. Boy!}). | |
116 | ||
117 | In this example, point is initially at the beginning of the buffer; the | |
118 | search leaves it between the @samp{y} and the @samp{!}. | |
119 | ||
120 | @example | |
121 | @group | |
122 | ---------- Buffer: foo ---------- | |
123 | @point{}He said "Please! Find | |
124 | the ball boy!" | |
125 | ---------- Buffer: foo ---------- | |
126 | @end group | |
127 | ||
128 | @group | |
129 | (word-search-forward "Please find the ball, boy.") | |
130 | @result{} 35 | |
131 | ||
132 | ---------- Buffer: foo ---------- | |
133 | He said "Please! Find | |
134 | the ball boy@point{}!" | |
135 | ---------- Buffer: foo ---------- | |
136 | @end group | |
137 | @end example | |
138 | ||
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139 | If @var{limit} is non-@code{nil}, it must be a position in the current |
140 | buffer; it specifies the upper bound to the search. The match found | |
141 | must not extend after that position. | |
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142 | |
143 | If @var{noerror} is @code{nil}, then @code{word-search-forward} signals | |
144 | an error if the search fails. If @var{noerror} is @code{t}, then it | |
145 | returns @code{nil} instead of signaling an error. If @var{noerror} is | |
146 | neither @code{nil} nor @code{t}, it moves point to @var{limit} (or the | |
bcb6b6b8 | 147 | end of the accessible portion of the buffer) and returns @code{nil}. |
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148 | |
149 | If @var{repeat} is non-@code{nil}, then the search is repeated that many | |
150 | times. Point is positioned at the end of the last match. | |
151 | @end deffn | |
152 | ||
153 | @deffn Command word-search-backward string &optional limit noerror repeat | |
154 | This function searches backward from point for a word match to | |
155 | @var{string}. This function is just like @code{word-search-forward} | |
156 | except that it searches backward and normally leaves point at the | |
157 | beginning of the match. | |
158 | @end deffn | |
159 | ||
160 | @node Regular Expressions | |
161 | @section Regular Expressions | |
162 | @cindex regular expression | |
163 | @cindex regexp | |
164 | ||
165 | A @dfn{regular expression} (@dfn{regexp}, for short) is a pattern that | |
166 | denotes a (possibly infinite) set of strings. Searching for matches for | |
167 | a regexp is a very powerful operation. This section explains how to write | |
168 | regexps; the following section says how to search for them. | |
169 | ||
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170 | @findex re-builder |
171 | @cindex authoring regular expressions | |
172 | For convenient interactive development of regular expressions, you | |
173 | can use the @kbd{M-x re-builder} command. It provides a convenient | |
174 | interface for creating regular expressions, by giving immediate visual | |
175 | feedback in a separate buffer. As you edit the regexp, all its | |
176 | matches in the target buffer are highlighted. Each parenthesized | |
177 | sub-expression of the regexp is shown in a distinct face, which makes | |
178 | it easier to verify even very complex regexps. | |
179 | ||
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180 | @menu |
181 | * Syntax of Regexps:: Rules for writing regular expressions. | |
182 | * Regexp Example:: Illustrates regular expression syntax. | |
bcb6b6b8 | 183 | * Regexp Functions:: Functions for operating on regular expressions. |
7015aca4 RS |
184 | @end menu |
185 | ||
186 | @node Syntax of Regexps | |
187 | @subsection Syntax of Regular Expressions | |
188 | ||
61cfa852 RS |
189 | Regular expressions have a syntax in which a few characters are |
190 | special constructs and the rest are @dfn{ordinary}. An ordinary | |
191 | character is a simple regular expression that matches that character and | |
192 | nothing else. The special characters are @samp{.}, @samp{*}, @samp{+}, | |
193 | @samp{?}, @samp{[}, @samp{]}, @samp{^}, @samp{$}, and @samp{\}; no new | |
194 | special characters will be defined in the future. Any other character | |
195 | appearing in a regular expression is ordinary, unless a @samp{\} | |
196 | precedes it. | |
7015aca4 | 197 | |
8241495d | 198 | For example, @samp{f} is not a special character, so it is ordinary, and |
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199 | therefore @samp{f} is a regular expression that matches the string |
200 | @samp{f} and no other string. (It does @emph{not} match the string | |
8241495d RS |
201 | @samp{fg}, but it does match a @emph{part} of that string.) Likewise, |
202 | @samp{o} is a regular expression that matches only @samp{o}.@refill | |
7015aca4 | 203 | |
8241495d | 204 | Any two regular expressions @var{a} and @var{b} can be concatenated. The |
61cfa852 | 205 | result is a regular expression that matches a string if @var{a} matches |
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206 | some amount of the beginning of that string and @var{b} matches the rest of |
207 | the string.@refill | |
208 | ||
8241495d | 209 | As a simple example, we can concatenate the regular expressions @samp{f} |
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210 | and @samp{o} to get the regular expression @samp{fo}, which matches only |
211 | the string @samp{fo}. Still trivial. To do something more powerful, you | |
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212 | need to use one of the special regular expression constructs. |
213 | ||
214 | @menu | |
215 | * Regexp Special:: Special characters in regular expressions. | |
216 | * Char Classes:: Character classes used in regular expressions. | |
217 | * Regexp Backslash:: Backslash-sequences in regular expressions. | |
218 | @end menu | |
219 | ||
220 | @node Regexp Special | |
221 | @subsubsection Special Characters in Regular Expressions | |
222 | ||
223 | Here is a list of the characters that are special in a regular | |
224 | expression. | |
7015aca4 | 225 | |
7dd3d99f | 226 | @need 800 |
969fe9b5 RS |
227 | @table @asis |
228 | @item @samp{.}@: @r{(Period)} | |
7015aca4 RS |
229 | @cindex @samp{.} in regexp |
230 | is a special character that matches any single character except a newline. | |
231 | Using concatenation, we can make regular expressions like @samp{a.b}, which | |
232 | matches any three-character string that begins with @samp{a} and ends with | |
233 | @samp{b}.@refill | |
234 | ||
969fe9b5 | 235 | @item @samp{*} |
7015aca4 | 236 | @cindex @samp{*} in regexp |
1cd71ce0 RS |
237 | is not a construct by itself; it is a postfix operator that means to |
238 | match the preceding regular expression repetitively as many times as | |
239 | possible. Thus, @samp{o*} matches any number of @samp{o}s (including no | |
240 | @samp{o}s). | |
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241 | |
242 | @samp{*} always applies to the @emph{smallest} possible preceding | |
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243 | expression. Thus, @samp{fo*} has a repeating @samp{o}, not a repeating |
244 | @samp{fo}. It matches @samp{f}, @samp{fo}, @samp{foo}, and so on. | |
7015aca4 | 245 | |
f9f59935 RS |
246 | The matcher processes a @samp{*} construct by matching, immediately, as |
247 | many repetitions as can be found. Then it continues with the rest of | |
248 | the pattern. If that fails, backtracking occurs, discarding some of the | |
249 | matches of the @samp{*}-modified construct in the hope that that will | |
250 | make it possible to match the rest of the pattern. For example, in | |
251 | matching @samp{ca*ar} against the string @samp{caaar}, the @samp{a*} | |
252 | first tries to match all three @samp{a}s; but the rest of the pattern is | |
7015aca4 | 253 | @samp{ar} and there is only @samp{r} left to match, so this try fails. |
f9f59935 RS |
254 | The next alternative is for @samp{a*} to match only two @samp{a}s. With |
255 | this choice, the rest of the regexp matches successfully.@refill | |
7015aca4 | 256 | |
342fd6cd RS |
257 | Nested repetition operators take a long time, or even forever, if they |
258 | lead to ambiguous matching. For example, trying to match the regular | |
259 | expression @samp{\(x+y*\)*a} against the string | |
260 | @samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz} could take hours before it | |
261 | ultimately fails. Emacs must try each way of grouping the 35 | |
262 | @samp{x}s before concluding that none of them can work. Even worse, | |
263 | @samp{\(x*\)*} can match the null string in infinitely many ways, so | |
264 | it causes an infinite loop. To avoid these problems, check nested | |
265 | repetitions carefully. | |
73031603 | 266 | |
969fe9b5 | 267 | @item @samp{+} |
7015aca4 | 268 | @cindex @samp{+} in regexp |
1cd71ce0 RS |
269 | is a postfix operator, similar to @samp{*} except that it must match |
270 | the preceding expression at least once. So, for example, @samp{ca+r} | |
7015aca4 RS |
271 | matches the strings @samp{car} and @samp{caaaar} but not the string |
272 | @samp{cr}, whereas @samp{ca*r} matches all three strings. | |
273 | ||
969fe9b5 | 274 | @item @samp{?} |
7015aca4 | 275 | @cindex @samp{?} in regexp |
f9f59935 | 276 | is a postfix operator, similar to @samp{*} except that it must match the |
1cd71ce0 RS |
277 | preceding expression either once or not at all. For example, |
278 | @samp{ca?r} matches @samp{car} or @samp{cr}; nothing else. | |
7015aca4 | 279 | |
c082a348 RS |
280 | @item @samp{*?}, @samp{+?}, @samp{??} |
281 | These are ``non-greedy'' variants of the operators @samp{*}, @samp{+} | |
282 | and @samp{?}. Where those operators match the largest possible | |
283 | substring (consistent with matching the entire containing expression), | |
284 | the non-greedy variants match the smallest possible substring | |
285 | (consistent with matching the entire containing expression). | |
286 | ||
287 | For example, the regular expression @samp{c[ad]*a} when applied to the | |
288 | string @samp{cdaaada} matches the whole string; but the regular | |
289 | expression @samp{c[ad]*?a}, applied to that same string, matches just | |
290 | @samp{cda}. (The smallest possible match here for @samp{[ad]*?} that | |
291 | permits the whole expression to match is @samp{d}.) | |
292 | ||
969fe9b5 RS |
293 | @item @samp{[ @dots{} ]} |
294 | @cindex character alternative (in regexp) | |
7015aca4 RS |
295 | @cindex @samp{[} in regexp |
296 | @cindex @samp{]} in regexp | |
969fe9b5 RS |
297 | is a @dfn{character alternative}, which begins with @samp{[} and is |
298 | terminated by @samp{]}. In the simplest case, the characters between | |
299 | the two brackets are what this character alternative can match. | |
1cd71ce0 RS |
300 | |
301 | Thus, @samp{[ad]} matches either one @samp{a} or one @samp{d}, and | |
302 | @samp{[ad]*} matches any string composed of just @samp{a}s and @samp{d}s | |
303 | (including the empty string), from which it follows that @samp{c[ad]*r} | |
304 | matches @samp{cr}, @samp{car}, @samp{cdr}, @samp{caddaar}, etc. | |
305 | ||
969fe9b5 RS |
306 | You can also include character ranges in a character alternative, by |
307 | writing the starting and ending characters with a @samp{-} between them. | |
bcb6b6b8 LT |
308 | Thus, @samp{[a-z]} matches any lower-case @acronym{ASCII} letter. |
309 | Ranges may be intermixed freely with individual characters, as in | |
310 | @samp{[a-z$%.]}, which matches any lower case @acronym{ASCII} letter | |
311 | or @samp{$}, @samp{%} or period. | |
1cd71ce0 RS |
312 | |
313 | Note that the usual regexp special characters are not special inside a | |
86494bd5 | 314 | character alternative. A completely different set of characters is |
969fe9b5 | 315 | special inside character alternatives: @samp{]}, @samp{-} and @samp{^}. |
1cd71ce0 | 316 | |
969fe9b5 RS |
317 | To include a @samp{]} in a character alternative, you must make it the |
318 | first character. For example, @samp{[]a]} matches @samp{]} or @samp{a}. | |
319 | To include a @samp{-}, write @samp{-} as the first or last character of | |
320 | the character alternative, or put it after a range. Thus, @samp{[]-]} | |
321 | matches both @samp{]} and @samp{-}. | |
7015aca4 | 322 | |
969fe9b5 RS |
323 | To include @samp{^} in a character alternative, put it anywhere but at |
324 | the beginning. | |
7015aca4 | 325 | |
8f17d892 RS |
326 | The beginning and end of a range of multibyte characters must be in |
327 | the same character set (@pxref{Character Sets}). Thus, | |
328 | @code{"[\x8e0-\x97c]"} is invalid because character 0x8e0 (@samp{a} | |
329 | with grave accent) is in the Emacs character set for Latin-1 but the | |
330 | character 0x97c (@samp{u} with diaeresis) is in the Emacs character | |
331 | set for Latin-2. (We use Lisp string syntax to write that example, | |
332 | and a few others in the next few paragraphs, in order to include hex | |
333 | escape sequences in them.) | |
6cc089d2 DL |
334 | |
335 | If a range starts with a unibyte character @var{c} and ends with a | |
336 | multibyte character @var{c2}, the range is divided into two parts: one | |
337 | is @samp{@var{c}..?\377}, the other is @samp{@var{c1}..@var{c2}}, where | |
338 | @var{c1} is the first character of the charset to which @var{c2} | |
339 | belongs. | |
177c0ea7 | 340 | |
ad800164 | 341 | You cannot always match all non-@acronym{ASCII} characters with the regular |
8f17d892 | 342 | expression @code{"[\200-\377]"}. This works when searching a unibyte |
8241495d | 343 | buffer or string (@pxref{Text Representations}), but not in a multibyte |
ad800164 | 344 | buffer or string, because many non-@acronym{ASCII} characters have codes |
8f17d892 | 345 | above octal 0377. However, the regular expression @code{"[^\000-\177]"} |
ad800164 | 346 | does match all non-@acronym{ASCII} characters (see below regarding @samp{^}), |
8241495d | 347 | in both multibyte and unibyte representations, because only the |
ad800164 | 348 | @acronym{ASCII} characters are excluded. |
8241495d | 349 | |
63f508b4 | 350 | A character alternative can also specify named |
8241495d RS |
351 | character classes (@pxref{Char Classes}). This is a POSIX feature whose |
352 | syntax is @samp{[:@var{class}:]}. Using a character class is equivalent | |
353 | to mentioning each of the characters in that class; but the latter is | |
354 | not feasible in practice, since some classes include thousands of | |
355 | different characters. | |
356 | ||
969fe9b5 | 357 | @item @samp{[^ @dots{} ]} |
7015aca4 | 358 | @cindex @samp{^} in regexp |
342fd6cd RS |
359 | @samp{[^} begins a @dfn{complemented character alternative}. This |
360 | matches any character except the ones specified. Thus, | |
361 | @samp{[^a-z0-9A-Z]} matches all characters @emph{except} letters and | |
362 | digits. | |
7015aca4 | 363 | |
969fe9b5 | 364 | @samp{^} is not special in a character alternative unless it is the first |
7015aca4 | 365 | character. The character following the @samp{^} is treated as if it |
1cd71ce0 | 366 | were first (in other words, @samp{-} and @samp{]} are not special there). |
7015aca4 | 367 | |
969fe9b5 | 368 | A complemented character alternative can match a newline, unless newline is |
1cd71ce0 RS |
369 | mentioned as one of the characters not to match. This is in contrast to |
370 | the handling of regexps in programs such as @code{grep}. | |
7015aca4 | 371 | |
969fe9b5 | 372 | @item @samp{^} |
7015aca4 | 373 | @cindex beginning of line in regexp |
bcb6b6b8 LT |
374 | When matching a buffer, @samp{^} matches the empty string, but only at the |
375 | beginning of a line in the text being matched (or the beginning of the | |
376 | accessible portion of the buffer). Otherwise it fails to match | |
377 | anything. Thus, @samp{^foo} matches a @samp{foo} that occurs at the | |
378 | beginning of a line. | |
7015aca4 | 379 | |
61cfa852 | 380 | When matching a string instead of a buffer, @samp{^} matches at the |
8f17d892 | 381 | beginning of the string or after a newline character. |
7015aca4 | 382 | |
8241495d RS |
383 | For historical compatibility reasons, @samp{^} can be used only at the |
384 | beginning of the regular expression, or after @samp{\(} or @samp{\|}. | |
385 | ||
969fe9b5 | 386 | @item @samp{$} |
7015aca4 | 387 | @cindex @samp{$} in regexp |
8241495d | 388 | @cindex end of line in regexp |
bcb6b6b8 LT |
389 | is similar to @samp{^} but matches only at the end of a line (or the |
390 | end of the accessible portion of the buffer). Thus, @samp{x+$} | |
391 | matches a string of one @samp{x} or more at the end of a line. | |
7015aca4 | 392 | |
61cfa852 | 393 | When matching a string instead of a buffer, @samp{$} matches at the end |
8f17d892 | 394 | of the string or before a newline character. |
7015aca4 | 395 | |
8241495d RS |
396 | For historical compatibility reasons, @samp{$} can be used only at the |
397 | end of the regular expression, or before @samp{\)} or @samp{\|}. | |
398 | ||
969fe9b5 | 399 | @item @samp{\} |
7015aca4 RS |
400 | @cindex @samp{\} in regexp |
401 | has two functions: it quotes the special characters (including | |
402 | @samp{\}), and it introduces additional special constructs. | |
403 | ||
404 | Because @samp{\} quotes special characters, @samp{\$} is a regular | |
61cfa852 RS |
405 | expression that matches only @samp{$}, and @samp{\[} is a regular |
406 | expression that matches only @samp{[}, and so on. | |
7015aca4 RS |
407 | |
408 | Note that @samp{\} also has special meaning in the read syntax of Lisp | |
409 | strings (@pxref{String Type}), and must be quoted with @samp{\}. For | |
410 | example, the regular expression that matches the @samp{\} character is | |
411 | @samp{\\}. To write a Lisp string that contains the characters | |
412 | @samp{\\}, Lisp syntax requires you to quote each @samp{\} with another | |
413 | @samp{\}. Therefore, the read syntax for a regular expression matching | |
414 | @samp{\} is @code{"\\\\"}.@refill | |
415 | @end table | |
416 | ||
b22f3a19 | 417 | @strong{Please note:} For historical compatibility, special characters |
7015aca4 RS |
418 | are treated as ordinary ones if they are in contexts where their special |
419 | meanings make no sense. For example, @samp{*foo} treats @samp{*} as | |
420 | ordinary since there is no preceding expression on which the @samp{*} | |
61cfa852 RS |
421 | can act. It is poor practice to depend on this behavior; quote the |
422 | special character anyway, regardless of where it appears.@refill | |
7015aca4 | 423 | |
8241495d RS |
424 | @node Char Classes |
425 | @subsubsection Character Classes | |
426 | @cindex character classes in regexp | |
427 | ||
428 | Here is a table of the classes you can use in a character alternative, | |
63f508b4 | 429 | and what they mean: |
8241495d RS |
430 | |
431 | @table @samp | |
432 | @item [:ascii:] | |
ad800164 | 433 | This matches any @acronym{ASCII} (unibyte) character. |
8241495d RS |
434 | @item [:alnum:] |
435 | This matches any letter or digit. (At present, for multibyte | |
436 | characters, it matches anything that has word syntax.) | |
437 | @item [:alpha:] | |
438 | This matches any letter. (At present, for multibyte characters, it | |
439 | matches anything that has word syntax.) | |
440 | @item [:blank:] | |
441 | This matches space and tab only. | |
442 | @item [:cntrl:] | |
ad800164 | 443 | This matches any @acronym{ASCII} control character. |
8241495d RS |
444 | @item [:digit:] |
445 | This matches @samp{0} through @samp{9}. Thus, @samp{[-+[:digit:]]} | |
446 | matches any digit, as well as @samp{+} and @samp{-}. | |
447 | @item [:graph:] | |
ad800164 | 448 | This matches graphic characters---everything except @acronym{ASCII} control |
75708135 | 449 | characters, space, and the delete character. |
8241495d RS |
450 | @item [:lower:] |
451 | This matches any lower-case letter, as determined by | |
452 | the current case table (@pxref{Case Tables}). | |
453 | @item [:nonascii:] | |
ad800164 | 454 | This matches any non-@acronym{ASCII} (multibyte) character. |
8241495d | 455 | @item [:print:] |
ad800164 | 456 | This matches printing characters---everything except @acronym{ASCII} control |
caccdcbb | 457 | characters and the delete character. |
8241495d RS |
458 | @item [:punct:] |
459 | This matches any punctuation character. (At present, for multibyte | |
460 | characters, it matches anything that has non-word syntax.) | |
461 | @item [:space:] | |
462 | This matches any character that has whitespace syntax | |
463 | (@pxref{Syntax Class Table}). | |
464 | @item [:upper:] | |
465 | This matches any upper-case letter, as determined by | |
466 | the current case table (@pxref{Case Tables}). | |
467 | @item [:word:] | |
468 | This matches any character that has word syntax (@pxref{Syntax Class | |
469 | Table}). | |
470 | @item [:xdigit:] | |
471 | This matches the hexadecimal digits: @samp{0} through @samp{9}, @samp{a} | |
472 | through @samp{f} and @samp{A} through @samp{F}. | |
473 | @end table | |
474 | ||
475 | @node Regexp Backslash | |
476 | @subsubsection Backslash Constructs in Regular Expressions | |
477 | ||
478 | For the most part, @samp{\} followed by any character matches only | |
479 | that character. However, there are several exceptions: certain | |
480 | two-character sequences starting with @samp{\} that have special | |
481 | meanings. (The character after the @samp{\} in such a sequence is | |
482 | always ordinary when used on its own.) Here is a table of the special | |
483 | @samp{\} constructs. | |
7015aca4 | 484 | |
969fe9b5 | 485 | @table @samp |
7015aca4 RS |
486 | @item \| |
487 | @cindex @samp{|} in regexp | |
488 | @cindex regexp alternative | |
489 | specifies an alternative. | |
490 | Two regular expressions @var{a} and @var{b} with @samp{\|} in | |
491 | between form an expression that matches anything that either @var{a} or | |
492 | @var{b} matches.@refill | |
493 | ||
494 | Thus, @samp{foo\|bar} matches either @samp{foo} or @samp{bar} | |
495 | but no other string.@refill | |
496 | ||
497 | @samp{\|} applies to the largest possible surrounding expressions. Only a | |
498 | surrounding @samp{\( @dots{} \)} grouping can limit the grouping power of | |
499 | @samp{\|}.@refill | |
500 | ||
01913af2 RS |
501 | If you need full backtracking capability to handle multiple uses of |
502 | @samp{\|}, use the POSIX regular expression functions (@pxref{POSIX | |
503 | Regexps}). | |
7015aca4 | 504 | |
2d06696f RS |
505 | @item \@{@var{m}\@} |
506 | is a postfix operator that repeats the previous pattern exactly @var{m} | |
507 | times. Thus, @samp{x\@{5\@}} matches the string @samp{xxxxx} | |
508 | and nothing else. @samp{c[ad]\@{3\@}r} matches string such as | |
509 | @samp{caaar}, @samp{cdddr}, @samp{cadar}, and so on. | |
510 | ||
511 | @item \@{@var{m},@var{n}\@} | |
2a233172 | 512 | is a more general postfix operator that specifies repetition with a |
2d06696f RS |
513 | minimum of @var{m} repeats and a maximum of @var{n} repeats. If @var{m} |
514 | is omitted, the minimum is 0; if @var{n} is omitted, there is no | |
515 | maximum. | |
516 | ||
517 | For example, @samp{c[ad]\@{1,2\@}r} matches the strings @samp{car}, | |
518 | @samp{cdr}, @samp{caar}, @samp{cadr}, @samp{cdar}, and @samp{cddr}, and | |
519 | nothing else.@* | |
520 | @samp{\@{0,1\@}} or @samp{\@{,1\@}} is equivalent to @samp{?}. @* | |
521 | @samp{\@{0,\@}} or @samp{\@{,\@}} is equivalent to @samp{*}. @* | |
522 | @samp{\@{1,\@}} is equivalent to @samp{+}. | |
523 | ||
7015aca4 RS |
524 | @item \( @dots{} \) |
525 | @cindex @samp{(} in regexp | |
526 | @cindex @samp{)} in regexp | |
527 | @cindex regexp grouping | |
528 | is a grouping construct that serves three purposes: | |
529 | ||
530 | @enumerate | |
531 | @item | |
9e2b495b RS |
532 | To enclose a set of @samp{\|} alternatives for other operations. Thus, |
533 | the regular expression @samp{\(foo\|bar\)x} matches either @samp{foox} | |
534 | or @samp{barx}. | |
7015aca4 RS |
535 | |
536 | @item | |
1cd71ce0 RS |
537 | To enclose a complicated expression for the postfix operators @samp{*}, |
538 | @samp{+} and @samp{?} to operate on. Thus, @samp{ba\(na\)*} matches | |
a9f0a989 RS |
539 | @samp{ba}, @samp{bana}, @samp{banana}, @samp{bananana}, etc., with any |
540 | number (zero or more) of @samp{na} strings. | |
7015aca4 RS |
541 | |
542 | @item | |
2d06696f RS |
543 | To record a matched substring for future reference with |
544 | @samp{\@var{digit}} (see below). | |
7015aca4 RS |
545 | @end enumerate |
546 | ||
547 | This last application is not a consequence of the idea of a | |
2d06696f RS |
548 | parenthetical grouping; it is a separate feature that was assigned as a |
549 | second meaning to the same @samp{\( @dots{} \)} construct because, in | |
a39c2e0d | 550 | practice, there was usually no conflict between the two meanings. But |
2d06696f RS |
551 | occasionally there is a conflict, and that led to the introduction of |
552 | shy groups. | |
553 | ||
554 | @item \(?: @dots{} \) | |
555 | is the @dfn{shy group} construct. A shy group serves the first two | |
556 | purposes of an ordinary group (controlling the nesting of other | |
557 | operators), but it does not get a number, so you cannot refer back to | |
558 | its value with @samp{\@var{digit}}. | |
559 | ||
bcb6b6b8 | 560 | Shy groups are particularly useful for mechanically-constructed regular |
2d06696f RS |
561 | expressions because they can be added automatically without altering the |
562 | numbering of any ordinary, non-shy groups. | |
7015aca4 RS |
563 | |
564 | @item \@var{digit} | |
61cfa852 | 565 | matches the same text that matched the @var{digit}th occurrence of a |
a5d0a32e | 566 | grouping (@samp{\( @dots{} \)}) construct. |
7015aca4 | 567 | |
a5d0a32e RS |
568 | In other words, after the end of a group, the matcher remembers the |
569 | beginning and end of the text matched by that group. Later on in the | |
570 | regular expression you can use @samp{\} followed by @var{digit} to | |
571 | match that same text, whatever it may have been. | |
7015aca4 | 572 | |
a5d0a32e RS |
573 | The strings matching the first nine grouping constructs appearing in |
574 | the entire regular expression passed to a search or matching function | |
575 | are assigned numbers 1 through 9 in the order that the open | |
576 | parentheses appear in the regular expression. So you can use | |
577 | @samp{\1} through @samp{\9} to refer to the text matched by the | |
578 | corresponding grouping constructs. | |
7015aca4 RS |
579 | |
580 | For example, @samp{\(.*\)\1} matches any newline-free string that is | |
581 | composed of two identical halves. The @samp{\(.*\)} matches the first | |
582 | half, which may be anything, but the @samp{\1} that follows must match | |
583 | the same exact text. | |
584 | ||
bcb6b6b8 LT |
585 | If a @samp{\( @dots{} \)} construct matches more than once (which can |
586 | happen, for instance, if it is followed by @samp{*}), only the last | |
587 | match is recorded. | |
588 | ||
a5d0a32e RS |
589 | If a particular grouping construct in the regular expression was never |
590 | matched---for instance, if it appears inside of an alternative that | |
591 | wasn't used, or inside of a repetition that repeated zero times---then | |
592 | the corresponding @samp{\@var{digit}} construct never matches | |
593 | anything. To use an artificial example,, @samp{\(foo\(b*\)\|lose\)\2} | |
594 | cannot match @samp{lose}: the second alternative inside the larger | |
595 | group matches it, but then @samp{\2} is undefined and can't match | |
596 | anything. But it can match @samp{foobb}, because the first | |
597 | alternative matches @samp{foob} and @samp{\2} matches @samp{b}. | |
598 | ||
7015aca4 RS |
599 | @item \w |
600 | @cindex @samp{\w} in regexp | |
601 | matches any word-constituent character. The editor syntax table | |
602 | determines which characters these are. @xref{Syntax Tables}. | |
603 | ||
604 | @item \W | |
605 | @cindex @samp{\W} in regexp | |
61cfa852 | 606 | matches any character that is not a word constituent. |
7015aca4 RS |
607 | |
608 | @item \s@var{code} | |
609 | @cindex @samp{\s} in regexp | |
610 | matches any character whose syntax is @var{code}. Here @var{code} is a | |
61cfa852 | 611 | character that represents a syntax code: thus, @samp{w} for word |
7015aca4 | 612 | constituent, @samp{-} for whitespace, @samp{(} for open parenthesis, |
f9f59935 RS |
613 | etc. To represent whitespace syntax, use either @samp{-} or a space |
614 | character. @xref{Syntax Class Table}, for a list of syntax codes and | |
615 | the characters that stand for them. | |
7015aca4 RS |
616 | |
617 | @item \S@var{code} | |
618 | @cindex @samp{\S} in regexp | |
619 | matches any character whose syntax is not @var{code}. | |
a8b5bbef DL |
620 | |
621 | @item \c@var{c} | |
622 | matches any character whose category is @var{c}. Here @var{c} is a | |
623 | character that represents a category: thus, @samp{c} for Chinese | |
624 | characters or @samp{g} for Greek characters in the standard category | |
625 | table. | |
626 | ||
627 | @item \C@var{c} | |
628 | matches any character whose category is not @var{c}. | |
7015aca4 RS |
629 | @end table |
630 | ||
61cfa852 | 631 | The following regular expression constructs match the empty string---that is, |
7015aca4 | 632 | they don't use up any characters---but whether they match depends on the |
bcb6b6b8 LT |
633 | context. For all, the beginning and end of the accessible portion of |
634 | the buffer are treated as if they were the actual beginning and end of | |
635 | the buffer. | |
7015aca4 | 636 | |
969fe9b5 | 637 | @table @samp |
7015aca4 RS |
638 | @item \` |
639 | @cindex @samp{\`} in regexp | |
640 | matches the empty string, but only at the beginning | |
641 | of the buffer or string being matched against. | |
642 | ||
643 | @item \' | |
644 | @cindex @samp{\'} in regexp | |
645 | matches the empty string, but only at the end of | |
646 | the buffer or string being matched against. | |
647 | ||
648 | @item \= | |
649 | @cindex @samp{\=} in regexp | |
650 | matches the empty string, but only at point. | |
651 | (This construct is not defined when matching against a string.) | |
652 | ||
653 | @item \b | |
654 | @cindex @samp{\b} in regexp | |
655 | matches the empty string, but only at the beginning or | |
656 | end of a word. Thus, @samp{\bfoo\b} matches any occurrence of | |
657 | @samp{foo} as a separate word. @samp{\bballs?\b} matches | |
658 | @samp{ball} or @samp{balls} as a separate word.@refill | |
659 | ||
bcb6b6b8 | 660 | @samp{\b} matches at the beginning or end of the buffer (or string) |
1cd71ce0 RS |
661 | regardless of what text appears next to it. |
662 | ||
7015aca4 RS |
663 | @item \B |
664 | @cindex @samp{\B} in regexp | |
665 | matches the empty string, but @emph{not} at the beginning or | |
bcb6b6b8 | 666 | end of a word, nor at the beginning or end of the buffer (or string). |
7015aca4 RS |
667 | |
668 | @item \< | |
669 | @cindex @samp{\<} in regexp | |
670 | matches the empty string, but only at the beginning of a word. | |
bcb6b6b8 | 671 | @samp{\<} matches at the beginning of the buffer (or string) only if a |
1cd71ce0 | 672 | word-constituent character follows. |
7015aca4 RS |
673 | |
674 | @item \> | |
675 | @cindex @samp{\>} in regexp | |
1cd71ce0 | 676 | matches the empty string, but only at the end of a word. @samp{\>} |
bcb6b6b8 LT |
677 | matches at the end of the buffer (or string) only if the contents end |
678 | with a word-constituent character. | |
9a7e97c6 LT |
679 | |
680 | @item \_< | |
681 | @cindex @samp{\_<} in regexp | |
682 | matches the empty string, but only at the beginning of a symbol. A | |
683 | symbol is a sequence of one or more word or symbol constituent | |
684 | characters. @samp{\_<} matches at the beginning of the buffer (or | |
685 | string) only if a symbol-constituent character follows. | |
686 | ||
687 | @item \_> | |
688 | @cindex @samp{\_>} in regexp | |
689 | matches the empty string, but only at the end of a symbol. @samp{\_>} | |
690 | matches at the end of the buffer (or string) only if the contents end | |
691 | with a symbol-constituent character. | |
7015aca4 RS |
692 | @end table |
693 | ||
694 | @kindex invalid-regexp | |
695 | Not every string is a valid regular expression. For example, a string | |
696 | with unbalanced square brackets is invalid (with a few exceptions, such | |
61cfa852 | 697 | as @samp{[]]}), and so is a string that ends with a single @samp{\}. If |
7015aca4 RS |
698 | an invalid regular expression is passed to any of the search functions, |
699 | an @code{invalid-regexp} error is signaled. | |
700 | ||
7015aca4 RS |
701 | @node Regexp Example |
702 | @comment node-name, next, previous, up | |
703 | @subsection Complex Regexp Example | |
704 | ||
bcb6b6b8 LT |
705 | Here is a complicated regexp which was formerly used by Emacs to |
706 | recognize the end of a sentence together with any whitespace that | |
45fa30b2 LT |
707 | follows. (Nowadays Emacs uses a similar but more complex default |
708 | regexp constructed by the function @code{sentence-end}. | |
709 | @xref{Standard Regexps}.) | |
7015aca4 RS |
710 | |
711 | First, we show the regexp as a string in Lisp syntax to distinguish | |
712 | spaces from tab characters. The string constant begins and ends with a | |
713 | double-quote. @samp{\"} stands for a double-quote as part of the | |
714 | string, @samp{\\} for a backslash as part of the string, @samp{\t} for a | |
715 | tab and @samp{\n} for a newline. | |
716 | ||
717 | @example | |
bcb6b6b8 | 718 | "[.?!][]\"')@}]*\\($\\| $\\|\t\\|@ @ \\)[ \t\n]*" |
7015aca4 RS |
719 | @end example |
720 | ||
969fe9b5 | 721 | @noindent |
bcb6b6b8 | 722 | In contrast, if you evaluate this string, you will see the following: |
7015aca4 RS |
723 | |
724 | @example | |
725 | @group | |
bcb6b6b8 LT |
726 | "[.?!][]\"')@}]*\\($\\| $\\|\t\\|@ @ \\)[ \t\n]*" |
727 | @result{} "[.?!][]\"')@}]*\\($\\| $\\| \\|@ @ \\)[ | |
7015aca4 RS |
728 | ]*" |
729 | @end group | |
730 | @end example | |
731 | ||
732 | @noindent | |
733 | In this output, tab and newline appear as themselves. | |
734 | ||
735 | This regular expression contains four parts in succession and can be | |
736 | deciphered as follows: | |
737 | ||
738 | @table @code | |
739 | @item [.?!] | |
969fe9b5 RS |
740 | The first part of the pattern is a character alternative that matches |
741 | any one of three characters: period, question mark, and exclamation | |
bcb6b6b8 | 742 | mark. The match must begin with one of these three characters. (This |
45fa30b2 LT |
743 | is one point where the new default regexp used by Emacs differs from |
744 | the old. The new value also allows some non-@acronym{ASCII} | |
745 | characters that end a sentence without any following whitespace.) | |
7015aca4 RS |
746 | |
747 | @item []\"')@}]* | |
748 | The second part of the pattern matches any closing braces and quotation | |
749 | marks, zero or more of them, that may follow the period, question mark | |
750 | or exclamation mark. The @code{\"} is Lisp syntax for a double-quote in | |
751 | a string. The @samp{*} at the end indicates that the immediately | |
969fe9b5 | 752 | preceding regular expression (a character alternative, in this case) may be |
7015aca4 RS |
753 | repeated zero or more times. |
754 | ||
7fd1911a | 755 | @item \\($\\|@ $\\|\t\\|@ @ \\) |
7015aca4 | 756 | The third part of the pattern matches the whitespace that follows the |
f9f59935 RS |
757 | end of a sentence: the end of a line (optionally with a space), or a |
758 | tab, or two spaces. The double backslashes mark the parentheses and | |
759 | vertical bars as regular expression syntax; the parentheses delimit a | |
760 | group and the vertical bars separate alternatives. The dollar sign is | |
761 | used to match the end of a line. | |
7015aca4 RS |
762 | |
763 | @item [ \t\n]* | |
764 | Finally, the last part of the pattern matches any additional whitespace | |
765 | beyond the minimum needed to end a sentence. | |
766 | @end table | |
767 | ||
8241495d RS |
768 | @node Regexp Functions |
769 | @subsection Regular Expression Functions | |
770 | ||
771 | These functions operate on regular expressions. | |
772 | ||
773 | @defun regexp-quote string | |
774 | This function returns a regular expression whose only exact match is | |
775 | @var{string}. Using this regular expression in @code{looking-at} will | |
776 | succeed only if the next characters in the buffer are @var{string}; | |
777 | using it in a search function will succeed if the text being searched | |
778 | contains @var{string}. | |
779 | ||
780 | This allows you to request an exact string match or search when calling | |
781 | a function that wants a regular expression. | |
782 | ||
783 | @example | |
784 | @group | |
785 | (regexp-quote "^The cat$") | |
786 | @result{} "\\^The cat\\$" | |
787 | @end group | |
788 | @end example | |
789 | ||
790 | One use of @code{regexp-quote} is to combine an exact string match with | |
791 | context described as a regular expression. For example, this searches | |
792 | for the string that is the value of @var{string}, surrounded by | |
793 | whitespace: | |
794 | ||
795 | @example | |
796 | @group | |
797 | (re-search-forward | |
798 | (concat "\\s-" (regexp-quote string) "\\s-")) | |
799 | @end group | |
800 | @end example | |
801 | @end defun | |
802 | ||
803 | @defun regexp-opt strings &optional paren | |
8241495d | 804 | This function returns an efficient regular expression that will match |
bcb6b6b8 LT |
805 | any of the strings in the list @var{strings}. This is useful when you |
806 | need to make matching or searching as fast as possible---for example, | |
807 | for Font Lock mode. | |
8241495d RS |
808 | |
809 | If the optional argument @var{paren} is non-@code{nil}, then the | |
810 | returned regular expression is always enclosed by at least one | |
bcb6b6b8 LT |
811 | parentheses-grouping construct. If @var{paren} is @code{words}, then |
812 | that construct is additionally surrounded by @samp{\<} and @samp{\>}. | |
8241495d RS |
813 | |
814 | This simplified definition of @code{regexp-opt} produces a | |
815 | regular expression which is equivalent to the actual value | |
816 | (but not as efficient): | |
817 | ||
818 | @example | |
819 | (defun regexp-opt (strings paren) | |
820 | (let ((open-paren (if paren "\\(" "")) | |
821 | (close-paren (if paren "\\)" ""))) | |
822 | (concat open-paren | |
823 | (mapconcat 'regexp-quote strings "\\|") | |
824 | close-paren))) | |
825 | @end example | |
826 | @end defun | |
827 | ||
828 | @defun regexp-opt-depth regexp | |
8241495d | 829 | This function returns the total number of grouping constructs |
bcb6b6b8 LT |
830 | (parenthesized expressions) in @var{regexp}. (This does not include |
831 | shy groups.) | |
8241495d RS |
832 | @end defun |
833 | ||
7015aca4 RS |
834 | @node Regexp Search |
835 | @section Regular Expression Searching | |
836 | @cindex regular expression searching | |
837 | @cindex regexp searching | |
838 | @cindex searching for regexp | |
839 | ||
969fe9b5 RS |
840 | In GNU Emacs, you can search for the next match for a regular |
841 | expression either incrementally or not. For incremental search | |
842 | commands, see @ref{Regexp Search, , Regular Expression Search, emacs, | |
843 | The GNU Emacs Manual}. Here we describe only the search functions | |
844 | useful in programs. The principal one is @code{re-search-forward}. | |
7015aca4 | 845 | |
f9f59935 RS |
846 | These search functions convert the regular expression to multibyte if |
847 | the buffer is multibyte; they convert the regular expression to unibyte | |
848 | if the buffer is unibyte. @xref{Text Representations}. | |
849 | ||
7015aca4 RS |
850 | @deffn Command re-search-forward regexp &optional limit noerror repeat |
851 | This function searches forward in the current buffer for a string of | |
852 | text that is matched by the regular expression @var{regexp}. The | |
853 | function skips over any amount of text that is not matched by | |
854 | @var{regexp}, and leaves point at the end of the first match found. | |
855 | It returns the new value of point. | |
856 | ||
5bb8ca2a RS |
857 | If @var{limit} is non-@code{nil}, it must be a position in the current |
858 | buffer. It specifies the upper bound to the search. No match | |
859 | extending after that position is accepted. | |
7015aca4 | 860 | |
5bb8ca2a RS |
861 | If @var{repeat} is supplied, it must be a positive number; the search |
862 | is repeated that many times; each repetition starts at the end of the | |
4362c714 RS |
863 | previous match. If all these successive searches succeed, the search |
864 | succeeds, moving point and returning its new value. Otherwise the | |
865 | search fails. What @code{re-search-forward} does when the search | |
866 | fails depends on the value of @var{noerror}: | |
f9f59935 | 867 | |
4362c714 RS |
868 | @table @asis |
869 | @item @code{nil} | |
870 | Signal a @code{search-failed} error. | |
871 | @item @code{t} | |
872 | Do nothing and return @code{nil}. | |
873 | @item anything else | |
874 | Move point to @var{limit} (or the end of the accessible portion of the | |
875 | buffer) and return @code{nil}. | |
876 | @end table | |
7015aca4 | 877 | |
7015aca4 RS |
878 | In the following example, point is initially before the @samp{T}. |
879 | Evaluating the search call moves point to the end of that line (between | |
880 | the @samp{t} of @samp{hat} and the newline). | |
881 | ||
882 | @example | |
883 | @group | |
884 | ---------- Buffer: foo ---------- | |
885 | I read "@point{}The cat in the hat | |
886 | comes back" twice. | |
887 | ---------- Buffer: foo ---------- | |
888 | @end group | |
889 | ||
890 | @group | |
891 | (re-search-forward "[a-z]+" nil t 5) | |
892 | @result{} 27 | |
893 | ||
894 | ---------- Buffer: foo ---------- | |
895 | I read "The cat in the hat@point{} | |
896 | comes back" twice. | |
897 | ---------- Buffer: foo ---------- | |
898 | @end group | |
899 | @end example | |
900 | @end deffn | |
901 | ||
902 | @deffn Command re-search-backward regexp &optional limit noerror repeat | |
903 | This function searches backward in the current buffer for a string of | |
904 | text that is matched by the regular expression @var{regexp}, leaving | |
905 | point at the beginning of the first text found. | |
906 | ||
7fd1911a RS |
907 | This function is analogous to @code{re-search-forward}, but they are not |
908 | simple mirror images. @code{re-search-forward} finds the match whose | |
909 | beginning is as close as possible to the starting point. If | |
910 | @code{re-search-backward} were a perfect mirror image, it would find the | |
911 | match whose end is as close as possible. However, in fact it finds the | |
bcb6b6b8 LT |
912 | match whose beginning is as close as possible (and yet ends before the |
913 | starting point). The reason for this is that matching a regular | |
914 | expression at a given spot always works from beginning to end, and | |
915 | starts at a specified beginning position. | |
7015aca4 RS |
916 | |
917 | A true mirror-image of @code{re-search-forward} would require a special | |
969fe9b5 RS |
918 | feature for matching regular expressions from end to beginning. It's |
919 | not worth the trouble of implementing that. | |
7015aca4 RS |
920 | @end deffn |
921 | ||
922 | @defun string-match regexp string &optional start | |
923 | This function returns the index of the start of the first match for | |
924 | the regular expression @var{regexp} in @var{string}, or @code{nil} if | |
925 | there is no match. If @var{start} is non-@code{nil}, the search starts | |
926 | at that index in @var{string}. | |
927 | ||
928 | For example, | |
929 | ||
930 | @example | |
931 | @group | |
932 | (string-match | |
933 | "quick" "The quick brown fox jumped quickly.") | |
934 | @result{} 4 | |
935 | @end group | |
936 | @group | |
937 | (string-match | |
938 | "quick" "The quick brown fox jumped quickly." 8) | |
939 | @result{} 27 | |
940 | @end group | |
941 | @end example | |
942 | ||
943 | @noindent | |
944 | The index of the first character of the | |
945 | string is 0, the index of the second character is 1, and so on. | |
946 | ||
947 | After this function returns, the index of the first character beyond | |
948 | the match is available as @code{(match-end 0)}. @xref{Match Data}. | |
949 | ||
950 | @example | |
951 | @group | |
952 | (string-match | |
953 | "quick" "The quick brown fox jumped quickly." 8) | |
954 | @result{} 27 | |
955 | @end group | |
956 | ||
957 | @group | |
958 | (match-end 0) | |
959 | @result{} 32 | |
960 | @end group | |
961 | @end example | |
962 | @end defun | |
963 | ||
964 | @defun looking-at regexp | |
965 | This function determines whether the text in the current buffer directly | |
966 | following point matches the regular expression @var{regexp}. ``Directly | |
967 | following'' means precisely that: the search is ``anchored'' and it can | |
968 | succeed only starting with the first character following point. The | |
969 | result is @code{t} if so, @code{nil} otherwise. | |
970 | ||
971 | This function does not move point, but it updates the match data, which | |
972 | you can access using @code{match-beginning} and @code{match-end}. | |
973 | @xref{Match Data}. | |
974 | ||
975 | In this example, point is located directly before the @samp{T}. If it | |
976 | were anywhere else, the result would be @code{nil}. | |
977 | ||
978 | @example | |
979 | @group | |
980 | ---------- Buffer: foo ---------- | |
981 | I read "@point{}The cat in the hat | |
982 | comes back" twice. | |
983 | ---------- Buffer: foo ---------- | |
984 | ||
985 | (looking-at "The cat in the hat$") | |
986 | @result{} t | |
987 | @end group | |
988 | @end example | |
989 | @end defun | |
990 | ||
4d4d2d07 RS |
991 | @defun looking-back regexp &optional limit |
992 | This function returns @code{t} if @var{regexp} matches text before | |
993 | point, ending at point, and @code{nil} otherwise. | |
994 | ||
995 | Because regular expression matching works only going forward, this is | |
996 | implemented by searching backwards from point for a match that ends at | |
997 | point. That can be quite slow if it has to search a long distance. | |
998 | You can bound the time required by specifying @var{limit}, which says | |
999 | not to search before @var{limit}. In this case, the match that is | |
1000 | found must begin at or after @var{limit}. | |
1001 | ||
1002 | @example | |
1003 | @group | |
1004 | ---------- Buffer: foo ---------- | |
1005 | I read "@point{}The cat in the hat | |
1006 | comes back" twice. | |
1007 | ---------- Buffer: foo ---------- | |
1008 | ||
1009 | (looking-back "read \"" 3) | |
1010 | @result{} t | |
1011 | (looking-back "read \"" 4) | |
1012 | @result{} nil | |
1013 | @end group | |
1014 | @end example | |
1015 | @end defun | |
1016 | ||
fe83e8de | 1017 | @defvar search-spaces-regexp |
65b65d26 RS |
1018 | If this variable is non-@code{nil}, it should be a regular expression |
1019 | that says how to search for whitespace. In that case, any group of | |
5bb8ca2a RS |
1020 | spaces in a regular expression being searched for stands for use of |
1021 | this regular expression. However, spaces inside of constructs such as | |
1022 | @samp{[@dots{}]} and @samp{*}, @samp{+}, @samp{?} are not affected by | |
1023 | @code{search-spaces-regexp}. | |
1024 | ||
1025 | Since this variable affects all regular expression search and match | |
1026 | constructs, you should bind it temporarily for as small as possible | |
1027 | a part of the code. | |
65b65d26 RS |
1028 | @end defvar |
1029 | ||
22697dac KH |
1030 | @node POSIX Regexps |
1031 | @section POSIX Regular Expression Searching | |
1032 | ||
1033 | The usual regular expression functions do backtracking when necessary | |
1034 | to handle the @samp{\|} and repetition constructs, but they continue | |
1035 | this only until they find @emph{some} match. Then they succeed and | |
1036 | report the first match found. | |
1037 | ||
1038 | This section describes alternative search functions which perform the | |
1039 | full backtracking specified by the POSIX standard for regular expression | |
1040 | matching. They continue backtracking until they have tried all | |
1041 | possibilities and found all matches, so they can report the longest | |
1042 | match, as required by POSIX. This is much slower, so use these | |
1043 | functions only when you really need the longest match. | |
1044 | ||
01913af2 RS |
1045 | The POSIX search and match functions do not properly support the |
1046 | non-greedy repetition operators. This is because POSIX backtracking | |
1047 | conflicts with the semantics of non-greedy repetition. | |
1048 | ||
22697dac KH |
1049 | @defun posix-search-forward regexp &optional limit noerror repeat |
1050 | This is like @code{re-search-forward} except that it performs the full | |
1051 | backtracking specified by the POSIX standard for regular expression | |
1052 | matching. | |
1053 | @end defun | |
1054 | ||
1055 | @defun posix-search-backward regexp &optional limit noerror repeat | |
1056 | This is like @code{re-search-backward} except that it performs the full | |
1057 | backtracking specified by the POSIX standard for regular expression | |
1058 | matching. | |
1059 | @end defun | |
1060 | ||
1061 | @defun posix-looking-at regexp | |
1062 | This is like @code{looking-at} except that it performs the full | |
1063 | backtracking specified by the POSIX standard for regular expression | |
1064 | matching. | |
1065 | @end defun | |
1066 | ||
1067 | @defun posix-string-match regexp string &optional start | |
1068 | This is like @code{string-match} except that it performs the full | |
1069 | backtracking specified by the POSIX standard for regular expression | |
1070 | matching. | |
1071 | @end defun | |
1072 | ||
7015aca4 RS |
1073 | @ignore |
1074 | @deffn Command delete-matching-lines regexp | |
1075 | This function is identical to @code{delete-non-matching-lines}, save | |
1076 | that it deletes what @code{delete-non-matching-lines} keeps. | |
1077 | ||
1078 | In the example below, point is located on the first line of text. | |
1079 | ||
1080 | @example | |
1081 | @group | |
1082 | ---------- Buffer: foo ---------- | |
1083 | We hold these truths | |
1084 | to be self-evident, | |
1085 | that all men are created | |
1086 | equal, and that they are | |
1087 | ---------- Buffer: foo ---------- | |
1088 | @end group | |
1089 | ||
1090 | @group | |
1091 | (delete-matching-lines "the") | |
1092 | @result{} nil | |
1093 | ||
1094 | ---------- Buffer: foo ---------- | |
1095 | to be self-evident, | |
1096 | that all men are created | |
1097 | ---------- Buffer: foo ---------- | |
1098 | @end group | |
1099 | @end example | |
1100 | @end deffn | |
1101 | ||
1102 | @deffn Command flush-lines regexp | |
1103 | This function is the same as @code{delete-matching-lines}. | |
1104 | @end deffn | |
1105 | ||
1106 | @defun delete-non-matching-lines regexp | |
1107 | This function deletes all lines following point which don't | |
1108 | contain a match for the regular expression @var{regexp}. | |
1109 | @end defun | |
1110 | ||
1111 | @deffn Command keep-lines regexp | |
1112 | This function is the same as @code{delete-non-matching-lines}. | |
1113 | @end deffn | |
1114 | ||
1115 | @deffn Command how-many regexp | |
1116 | This function counts the number of matches for @var{regexp} there are in | |
1117 | the current buffer following point. It prints this number in | |
1118 | the echo area, returning the string printed. | |
1119 | @end deffn | |
1120 | ||
1121 | @deffn Command count-matches regexp | |
1122 | This function is a synonym of @code{how-many}. | |
1123 | @end deffn | |
1124 | ||
79ddc9c9 | 1125 | @deffn Command list-matching-lines regexp &optional nlines |
7015aca4 RS |
1126 | This function is a synonym of @code{occur}. |
1127 | Show all lines following point containing a match for @var{regexp}. | |
1128 | Display each line with @var{nlines} lines before and after, | |
1129 | or @code{-}@var{nlines} before if @var{nlines} is negative. | |
1130 | @var{nlines} defaults to @code{list-matching-lines-default-context-lines}. | |
1131 | Interactively it is the prefix arg. | |
1132 | ||
1133 | The lines are shown in a buffer named @samp{*Occur*}. | |
1134 | It serves as a menu to find any of the occurrences in this buffer. | |
86494bd5 | 1135 | @kbd{C-h m} (@code{describe-mode}) in that buffer gives help. |
7015aca4 RS |
1136 | @end deffn |
1137 | ||
1138 | @defopt list-matching-lines-default-context-lines | |
1139 | Default value is 0. | |
1140 | Default number of context lines to include around a @code{list-matching-lines} | |
1141 | match. A negative number means to include that many lines before the match. | |
1142 | A positive number means to include that many lines both before and after. | |
1143 | @end defopt | |
1144 | @end ignore | |
1145 | ||
1146 | @node Search and Replace | |
1147 | @section Search and Replace | |
1148 | @cindex replacement | |
1149 | ||
0031b6c3 RS |
1150 | @defun replace-regexp-in-string regexp rep string &optional fixedcase literal subexp start |
1151 | This function copies @var{string} and searches it for matches for | |
1152 | @var{regexp}, and replaces them with @var{rep}. It returns the | |
1153 | modified copy. If @var{start} is non-@code{nil}, the search for | |
1154 | matches starts at that index in @var{string}, so matches starting | |
1155 | before that index are not changed. | |
1156 | ||
1157 | This function uses @code{replace-match} to do the replacement, and it | |
1158 | passes the optional arguments @var{fixedcase}, @var{literal} and | |
1159 | @var{subexp} along to @code{replace-match}. | |
1160 | ||
1161 | Instead of a string, @var{rep} can be a function. In that case, | |
1162 | @code{replace-regexp-in-string} calls @var{rep} for each match, | |
1163 | passing the text of the match as its sole argument. It collects the | |
1164 | value @var{rep} returns and passes that to @code{replace-match} as the | |
1165 | replacement string. The match-data at this point are the result | |
1166 | of matching @var{regexp} against a substring of @var{string}. | |
1167 | @end defun | |
1168 | ||
09facbd2 | 1169 | @defun perform-replace from-string replacements query-flag regexp-flag delimited-flag &optional repeat-count map start end |
3da17c12 GM |
1170 | This function is the guts of @code{query-replace} and related |
1171 | commands. It searches for occurrences of @var{from-string} in the | |
1172 | text between positions @var{start} and @var{end} and replaces some or | |
09facbd2 | 1173 | all of them. If @var{start} is @code{nil} (or omitted), point is used |
bcb6b6b8 LT |
1174 | instead, and the end of the buffer's accessible portion is used for |
1175 | @var{end}. | |
3da17c12 GM |
1176 | |
1177 | If @var{query-flag} is @code{nil}, it replaces all | |
7015aca4 RS |
1178 | occurrences; otherwise, it asks the user what to do about each one. |
1179 | ||
1180 | If @var{regexp-flag} is non-@code{nil}, then @var{from-string} is | |
1181 | considered a regular expression; otherwise, it must match literally. If | |
1182 | @var{delimited-flag} is non-@code{nil}, then only replacements | |
1183 | surrounded by word boundaries are considered. | |
1184 | ||
1185 | The argument @var{replacements} specifies what to replace occurrences | |
1186 | with. If it is a string, that string is used. It can also be a list of | |
1187 | strings, to be used in cyclic order. | |
1188 | ||
13ede7fc | 1189 | If @var{replacements} is a cons cell, @code{(@var{function} |
8241495d RS |
1190 | . @var{data})}, this means to call @var{function} after each match to |
1191 | get the replacement text. This function is called with two arguments: | |
1192 | @var{data}, and the number of replacements already made. | |
1193 | ||
bda144f4 MW |
1194 | If @var{repeat-count} is non-@code{nil}, it should be an integer. Then |
1195 | it specifies how many times to use each of the strings in the | |
bcb6b6b8 | 1196 | @var{replacements} list before advancing cyclically to the next one. |
7015aca4 | 1197 | |
8241495d RS |
1198 | If @var{from-string} contains upper-case letters, then |
1199 | @code{perform-replace} binds @code{case-fold-search} to @code{nil}, and | |
1200 | it uses the @code{replacements} without altering the case of them. | |
1201 | ||
7015aca4 | 1202 | Normally, the keymap @code{query-replace-map} defines the possible user |
7fd1911a RS |
1203 | responses for queries. The argument @var{map}, if non-@code{nil}, is a |
1204 | keymap to use instead of @code{query-replace-map}. | |
bcb6b6b8 LT |
1205 | |
1206 | @strong{Usage note:} Do not use this function in your own programs | |
1207 | unless you want to do something very similar to what | |
1208 | @code{query-replace} does, including setting the mark and possibly | |
1209 | querying the user. For most purposes a simple loop like, for | |
1210 | instance: | |
1211 | ||
1212 | @example | |
1213 | (while (re-search-forward "foo[ \t]+bar" nil t) | |
1214 | (replace-match "foobar")) | |
1215 | @end example | |
1216 | ||
1217 | @noindent | |
1218 | is preferable. It runs faster and avoids side effects, such as | |
1219 | setting the mark. @xref{Replacing Match,, Replacing the Text that | |
1220 | Matched}, for a description of @code{replace-match}. | |
7015aca4 RS |
1221 | @end defun |
1222 | ||
1223 | @defvar query-replace-map | |
1224 | This variable holds a special keymap that defines the valid user | |
1225 | responses for @code{query-replace} and related functions, as well as | |
1226 | @code{y-or-n-p} and @code{map-y-or-n-p}. It is unusual in two ways: | |
1227 | ||
1228 | @itemize @bullet | |
1229 | @item | |
1230 | The ``key bindings'' are not commands, just symbols that are meaningful | |
1231 | to the functions that use this map. | |
1232 | ||
1233 | @item | |
f9f59935 RS |
1234 | Prefix keys are not supported; each key binding must be for a |
1235 | single-event key sequence. This is because the functions don't use | |
1236 | @code{read-key-sequence} to get the input; instead, they read a single | |
1237 | event and look it up ``by hand.'' | |
7015aca4 RS |
1238 | @end itemize |
1239 | @end defvar | |
1240 | ||
1241 | Here are the meaningful ``bindings'' for @code{query-replace-map}. | |
1242 | Several of them are meaningful only for @code{query-replace} and | |
1243 | friends. | |
1244 | ||
1245 | @table @code | |
1246 | @item act | |
1247 | Do take the action being considered---in other words, ``yes.'' | |
1248 | ||
1249 | @item skip | |
1250 | Do not take action for this question---in other words, ``no.'' | |
1251 | ||
1252 | @item exit | |
7fd1911a RS |
1253 | Answer this question ``no,'' and give up on the entire series of |
1254 | questions, assuming that the answers will be ``no.'' | |
7015aca4 RS |
1255 | |
1256 | @item act-and-exit | |
7fd1911a RS |
1257 | Answer this question ``yes,'' and give up on the entire series of |
1258 | questions, assuming that subsequent answers will be ``no.'' | |
7015aca4 RS |
1259 | |
1260 | @item act-and-show | |
1261 | Answer this question ``yes,'' but show the results---don't advance yet | |
1262 | to the next question. | |
1263 | ||
1264 | @item automatic | |
1265 | Answer this question and all subsequent questions in the series with | |
1266 | ``yes,'' without further user interaction. | |
1267 | ||
1268 | @item backup | |
1269 | Move back to the previous place that a question was asked about. | |
1270 | ||
1271 | @item edit | |
1272 | Enter a recursive edit to deal with this question---instead of any | |
1273 | other action that would normally be taken. | |
1274 | ||
1275 | @item delete-and-edit | |
1276 | Delete the text being considered, then enter a recursive edit to replace | |
1277 | it. | |
1278 | ||
1279 | @item recenter | |
1280 | Redisplay and center the window, then ask the same question again. | |
1281 | ||
1282 | @item quit | |
1283 | Perform a quit right away. Only @code{y-or-n-p} and related functions | |
1284 | use this answer. | |
1285 | ||
1286 | @item help | |
1287 | Display some help, then ask again. | |
1288 | @end table | |
1289 | ||
1290 | @node Match Data | |
1291 | @section The Match Data | |
1292 | @cindex match data | |
1293 | ||
3f63de1e | 1294 | Emacs keeps track of the start and end positions of the segments of |
2a233172 RS |
1295 | text found during a search. This means, for example, that you can |
1296 | search for a complex pattern, such as a date in an Rmail message, and | |
1297 | then extract parts of the match under control of the pattern. | |
7015aca4 RS |
1298 | |
1299 | Because the match data normally describe the most recent search only, | |
1300 | you must be careful not to do another search inadvertently between the | |
1301 | search you wish to refer back to and the use of the match data. If you | |
1302 | can't avoid another intervening search, you must save and restore the | |
1303 | match data around it, to prevent it from being overwritten. | |
1304 | ||
1305 | @menu | |
969fe9b5 | 1306 | * Replacing Match:: Replacing a substring that was matched. |
7015aca4 RS |
1307 | * Simple Match Data:: Accessing single items of match data, |
1308 | such as where a particular subexpression started. | |
7015aca4 RS |
1309 | * Entire Match Data:: Accessing the entire match data at once, as a list. |
1310 | * Saving Match Data:: Saving and restoring the match data. | |
1311 | @end menu | |
1312 | ||
969fe9b5 | 1313 | @node Replacing Match |
8241495d | 1314 | @subsection Replacing the Text that Matched |
969fe9b5 RS |
1315 | |
1316 | This function replaces the text matched by the last search with | |
1317 | @var{replacement}. | |
1318 | ||
1319 | @cindex case in replacements | |
1320 | @defun replace-match replacement &optional fixedcase literal string subexp | |
1321 | This function replaces the text in the buffer (or in @var{string}) that | |
1322 | was matched by the last search. It replaces that text with | |
1323 | @var{replacement}. | |
1324 | ||
1325 | If you did the last search in a buffer, you should specify @code{nil} | |
bcb6b6b8 LT |
1326 | for @var{string} and make sure that the current buffer when you call |
1327 | @code{replace-match} is the one in which you did the searching or | |
1328 | matching. Then @code{replace-match} does the replacement by editing | |
1329 | the buffer; it leaves point at the end of the replacement text, and | |
1330 | returns @code{t}. | |
969fe9b5 RS |
1331 | |
1332 | If you did the search in a string, pass the same string as @var{string}. | |
1333 | Then @code{replace-match} does the replacement by constructing and | |
1334 | returning a new string. | |
1335 | ||
2037b263 RS |
1336 | If @var{fixedcase} is non-@code{nil}, then @code{replace-match} uses |
1337 | the replacement text without case conversion; otherwise, it converts | |
1338 | the replacement text depending upon the capitalization of the text to | |
1339 | be replaced. If the original text is all upper case, this converts | |
1340 | the replacement text to upper case. If all words of the original text | |
1341 | are capitalized, this capitalizes all the words of the replacement | |
1342 | text. If all the words are one-letter and they are all upper case, | |
1343 | they are treated as capitalized words rather than all-upper-case | |
1344 | words. | |
969fe9b5 | 1345 | |
969fe9b5 RS |
1346 | If @var{literal} is non-@code{nil}, then @var{replacement} is inserted |
1347 | exactly as it is, the only alterations being case changes as needed. | |
1348 | If it is @code{nil} (the default), then the character @samp{\} is treated | |
1349 | specially. If a @samp{\} appears in @var{replacement}, then it must be | |
1350 | part of one of the following sequences: | |
1351 | ||
1352 | @table @asis | |
1353 | @item @samp{\&} | |
1354 | @cindex @samp{&} in replacement | |
1355 | @samp{\&} stands for the entire text being replaced. | |
1356 | ||
1357 | @item @samp{\@var{n}} | |
1358 | @cindex @samp{\@var{n}} in replacement | |
1359 | @samp{\@var{n}}, where @var{n} is a digit, stands for the text that | |
1360 | matched the @var{n}th subexpression in the original regexp. | |
1361 | Subexpressions are those expressions grouped inside @samp{\(@dots{}\)}. | |
bcb6b6b8 | 1362 | If the @var{n}th subexpression never matched, an empty string is substituted. |
969fe9b5 RS |
1363 | |
1364 | @item @samp{\\} | |
1365 | @cindex @samp{\} in replacement | |
1366 | @samp{\\} stands for a single @samp{\} in the replacement text. | |
1367 | @end table | |
1368 | ||
2037b263 RS |
1369 | These substitutions occur after case conversion, if any, |
1370 | so the strings they substitute are never case-converted. | |
1371 | ||
969fe9b5 RS |
1372 | If @var{subexp} is non-@code{nil}, that says to replace just |
1373 | subexpression number @var{subexp} of the regexp that was matched, not | |
1374 | the entire match. For example, after matching @samp{foo \(ba*r\)}, | |
1375 | calling @code{replace-match} with 1 as @var{subexp} means to replace | |
1376 | just the text that matched @samp{\(ba*r\)}. | |
1377 | @end defun | |
1378 | ||
7015aca4 RS |
1379 | @node Simple Match Data |
1380 | @subsection Simple Match Data Access | |
1381 | ||
22697dac | 1382 | This section explains how to use the match data to find out what was |
87bf725e | 1383 | matched by the last search or match operation, if it succeeded. |
22697dac KH |
1384 | |
1385 | You can ask about the entire matching text, or about a particular | |
1386 | parenthetical subexpression of a regular expression. The @var{count} | |
1387 | argument in the functions below specifies which. If @var{count} is | |
1388 | zero, you are asking about the entire match. If @var{count} is | |
1389 | positive, it specifies which subexpression you want. | |
1390 | ||
1391 | Recall that the subexpressions of a regular expression are those | |
1392 | expressions grouped with escaped parentheses, @samp{\(@dots{}\)}. The | |
1393 | @var{count}th subexpression is found by counting occurrences of | |
1394 | @samp{\(} from the beginning of the whole regular expression. The first | |
1395 | subexpression is numbered 1, the second 2, and so on. Only regular | |
1396 | expressions can have subexpressions---after a simple string search, the | |
1397 | only information available is about the entire match. | |
1398 | ||
a9f0a989 RS |
1399 | A search which fails may or may not alter the match data. In the |
1400 | past, a failing search did not do this, but we may change it in the | |
87bf725e RS |
1401 | future. So don't try to rely on the value of the match data after |
1402 | a failing search. | |
a9f0a989 | 1403 | |
22697dac KH |
1404 | @defun match-string count &optional in-string |
1405 | This function returns, as a string, the text matched in the last search | |
1406 | or match operation. It returns the entire text if @var{count} is zero, | |
1407 | or just the portion corresponding to the @var{count}th parenthetical | |
a5d0a32e | 1408 | subexpression, if @var{count} is positive. |
22697dac KH |
1409 | |
1410 | If the last such operation was done against a string with | |
1411 | @code{string-match}, then you should pass the same string as the | |
969fe9b5 | 1412 | argument @var{in-string}. After a buffer search or match, |
22697dac KH |
1413 | you should omit @var{in-string} or pass @code{nil} for it; but you |
1414 | should make sure that the current buffer when you call | |
1415 | @code{match-string} is the one in which you did the searching or | |
1416 | matching. | |
a5d0a32e RS |
1417 | |
1418 | The value is @code{nil} if @var{count} is out of range, or for a | |
1419 | subexpression inside a @samp{\|} alternative that wasn't used or a | |
1420 | repetition that repeated zero times. | |
22697dac | 1421 | @end defun |
7015aca4 | 1422 | |
79ddc9c9 | 1423 | @defun match-string-no-properties count &optional in-string |
f9f59935 RS |
1424 | This function is like @code{match-string} except that the result |
1425 | has no text properties. | |
1426 | @end defun | |
1427 | ||
7015aca4 RS |
1428 | @defun match-beginning count |
1429 | This function returns the position of the start of text matched by the | |
1430 | last regular expression searched for, or a subexpression of it. | |
1431 | ||
7fd1911a | 1432 | If @var{count} is zero, then the value is the position of the start of |
eaac2be1 | 1433 | the entire match. Otherwise, @var{count} specifies a subexpression in |
969fe9b5 | 1434 | the regular expression, and the value of the function is the starting |
22697dac KH |
1435 | position of the match for that subexpression. |
1436 | ||
1437 | The value is @code{nil} for a subexpression inside a @samp{\|} | |
a5d0a32e | 1438 | alternative that wasn't used or a repetition that repeated zero times. |
7015aca4 RS |
1439 | @end defun |
1440 | ||
1441 | @defun match-end count | |
22697dac KH |
1442 | This function is like @code{match-beginning} except that it returns the |
1443 | position of the end of the match, rather than the position of the | |
1444 | beginning. | |
7015aca4 RS |
1445 | @end defun |
1446 | ||
1447 | Here is an example of using the match data, with a comment showing the | |
1448 | positions within the text: | |
1449 | ||
1450 | @example | |
1451 | @group | |
1452 | (string-match "\\(qu\\)\\(ick\\)" | |
1453 | "The quick fox jumped quickly.") | |
177c0ea7 | 1454 | ;0123456789 |
7015aca4 RS |
1455 | @result{} 4 |
1456 | @end group | |
1457 | ||
22697dac KH |
1458 | @group |
1459 | (match-string 0 "The quick fox jumped quickly.") | |
1460 | @result{} "quick" | |
1461 | (match-string 1 "The quick fox jumped quickly.") | |
1462 | @result{} "qu" | |
1463 | (match-string 2 "The quick fox jumped quickly.") | |
1464 | @result{} "ick" | |
1465 | @end group | |
1466 | ||
7015aca4 RS |
1467 | @group |
1468 | (match-beginning 1) ; @r{The beginning of the match} | |
1469 | @result{} 4 ; @r{with @samp{qu} is at index 4.} | |
1470 | @end group | |
1471 | ||
1472 | @group | |
1473 | (match-beginning 2) ; @r{The beginning of the match} | |
1474 | @result{} 6 ; @r{with @samp{ick} is at index 6.} | |
1475 | @end group | |
1476 | ||
1477 | @group | |
1478 | (match-end 1) ; @r{The end of the match} | |
1479 | @result{} 6 ; @r{with @samp{qu} is at index 6.} | |
1480 | ||
1481 | (match-end 2) ; @r{The end of the match} | |
1482 | @result{} 9 ; @r{with @samp{ick} is at index 9.} | |
1483 | @end group | |
1484 | @end example | |
1485 | ||
1486 | Here is another example. Point is initially located at the beginning | |
1487 | of the line. Searching moves point to between the space and the word | |
1488 | @samp{in}. The beginning of the entire match is at the 9th character of | |
1489 | the buffer (@samp{T}), and the beginning of the match for the first | |
1490 | subexpression is at the 13th character (@samp{c}). | |
1491 | ||
1492 | @example | |
1493 | @group | |
1494 | (list | |
1495 | (re-search-forward "The \\(cat \\)") | |
1496 | (match-beginning 0) | |
1497 | (match-beginning 1)) | |
7fd1911a | 1498 | @result{} (9 9 13) |
7015aca4 RS |
1499 | @end group |
1500 | ||
1501 | @group | |
1502 | ---------- Buffer: foo ---------- | |
1503 | I read "The cat @point{}in the hat comes back" twice. | |
1504 | ^ ^ | |
1505 | 9 13 | |
1506 | ---------- Buffer: foo ---------- | |
1507 | @end group | |
1508 | @end example | |
1509 | ||
1510 | @noindent | |
1511 | (In this case, the index returned is a buffer position; the first | |
1512 | character of the buffer counts as 1.) | |
1513 | ||
7015aca4 RS |
1514 | @node Entire Match Data |
1515 | @subsection Accessing the Entire Match Data | |
1516 | ||
1517 | The functions @code{match-data} and @code{set-match-data} read or | |
1518 | write the entire match data, all at once. | |
1519 | ||
4e370af2 | 1520 | @defun match-data &optional integers reuse reseat |
8135a25a RS |
1521 | This function returns a list of positions (markers or integers) that |
1522 | record all the information on what text the last search matched. | |
1523 | Element zero is the position of the beginning of the match for the | |
1524 | whole expression; element one is the position of the end of the match | |
1525 | for the expression. The next two elements are the positions of the | |
1526 | beginning and end of the match for the first subexpression, and so on. | |
1527 | In general, element | |
37680279 | 1528 | @ifnottex |
7015aca4 | 1529 | number 2@var{n} |
37680279 | 1530 | @end ifnottex |
7015aca4 RS |
1531 | @tex |
1532 | number {\mathsurround=0pt $2n$} | |
1533 | @end tex | |
1534 | corresponds to @code{(match-beginning @var{n})}; and | |
1535 | element | |
37680279 | 1536 | @ifnottex |
7015aca4 | 1537 | number 2@var{n} + 1 |
37680279 | 1538 | @end ifnottex |
7015aca4 RS |
1539 | @tex |
1540 | number {\mathsurround=0pt $2n+1$} | |
1541 | @end tex | |
1542 | corresponds to @code{(match-end @var{n})}. | |
1543 | ||
8135a25a RS |
1544 | Normally all the elements are markers or @code{nil}, but if |
1545 | @var{integers} is non-@code{nil}, that means to use integers instead | |
1546 | of markers. (In that case, the buffer itself is appended as an | |
1547 | additional element at the end of the list, to facilitate complete | |
1548 | restoration of the match data.) If the last match was done on a | |
1549 | string with @code{string-match}, then integers are always used, | |
1550 | since markers can't point into a string. | |
bcb6b6b8 LT |
1551 | |
1552 | If @var{reuse} is non-@code{nil}, it should be a list. In that case, | |
1553 | @code{match-data} stores the match data in @var{reuse}. That is, | |
1554 | @var{reuse} is destructively modified. @var{reuse} does not need to | |
1555 | have the right length. If it is not long enough to contain the match | |
1556 | data, it is extended. If it is too long, the length of @var{reuse} | |
1557 | stays the same, but the elements that were not used are set to | |
8135a25a RS |
1558 | @code{nil}. The purpose of this feature is to reduce the need for |
1559 | garbage collection. | |
7015aca4 | 1560 | |
4e370af2 | 1561 | If @var{reseat} is non-@code{nil}, all markers on the @var{reuse} list |
68be435e | 1562 | are reseated to point to nowhere. |
4e370af2 | 1563 | |
7015aca4 RS |
1564 | As always, there must be no possibility of intervening searches between |
1565 | the call to a search function and the call to @code{match-data} that is | |
1566 | intended to access the match data for that search. | |
1567 | ||
1568 | @example | |
1569 | @group | |
1570 | (match-data) | |
1571 | @result{} (#<marker at 9 in foo> | |
1572 | #<marker at 17 in foo> | |
1573 | #<marker at 13 in foo> | |
1574 | #<marker at 17 in foo>) | |
1575 | @end group | |
1576 | @end example | |
1577 | @end defun | |
1578 | ||
4e370af2 | 1579 | @defun set-match-data match-list &optional reseat |
7015aca4 RS |
1580 | This function sets the match data from the elements of @var{match-list}, |
1581 | which should be a list that was the value of a previous call to | |
3ab8acb9 RS |
1582 | @code{match-data}. (More precisely, anything that has the same format |
1583 | will work.) | |
7015aca4 RS |
1584 | |
1585 | If @var{match-list} refers to a buffer that doesn't exist, you don't get | |
1586 | an error; that sets the match data in a meaningless but harmless way. | |
1587 | ||
4e370af2 | 1588 | If @var{reseat} is non-@code{nil}, all markers on the @var{match-list} list |
68be435e | 1589 | are reseated to point to nowhere. |
4e370af2 | 1590 | |
7015aca4 | 1591 | @findex store-match-data |
969fe9b5 | 1592 | @code{store-match-data} is a semi-obsolete alias for @code{set-match-data}. |
7015aca4 RS |
1593 | @end defun |
1594 | ||
1595 | @node Saving Match Data | |
1596 | @subsection Saving and Restoring the Match Data | |
1597 | ||
d1280259 RS |
1598 | When you call a function that may do a search, you may need to save |
1599 | and restore the match data around that call, if you want to preserve the | |
1600 | match data from an earlier search for later use. Here is an example | |
1601 | that shows the problem that arises if you fail to save the match data: | |
7015aca4 RS |
1602 | |
1603 | @example | |
1604 | @group | |
1605 | (re-search-forward "The \\(cat \\)") | |
1606 | @result{} 48 | |
1607 | (foo) ; @r{Perhaps @code{foo} does} | |
1608 | ; @r{more searching.} | |
1609 | (match-end 0) | |
1610 | @result{} 61 ; @r{Unexpected result---not 48!} | |
1611 | @end group | |
1612 | @end example | |
1613 | ||
d1280259 | 1614 | You can save and restore the match data with @code{save-match-data}: |
7015aca4 | 1615 | |
bfe721d1 | 1616 | @defmac save-match-data body@dots{} |
1911e6e5 | 1617 | This macro executes @var{body}, saving and restoring the match |
bcb6b6b8 LT |
1618 | data around it. The return value is the value of the last form in |
1619 | @var{body}. | |
bfe721d1 | 1620 | @end defmac |
7015aca4 | 1621 | |
969fe9b5 RS |
1622 | You could use @code{set-match-data} together with @code{match-data} to |
1623 | imitate the effect of the special form @code{save-match-data}. Here is | |
1624 | how: | |
7015aca4 RS |
1625 | |
1626 | @example | |
1627 | @group | |
1628 | (let ((data (match-data))) | |
1629 | (unwind-protect | |
f9f59935 | 1630 | @dots{} ; @r{Ok to change the original match data.} |
7015aca4 RS |
1631 | (set-match-data data))) |
1632 | @end group | |
1633 | @end example | |
1634 | ||
d1280259 RS |
1635 | Emacs automatically saves and restores the match data when it runs |
1636 | process filter functions (@pxref{Filter Functions}) and process | |
1637 | sentinels (@pxref{Sentinels}). | |
1638 | ||
7015aca4 RS |
1639 | @ignore |
1640 | Here is a function which restores the match data provided the buffer | |
1641 | associated with it still exists. | |
1642 | ||
1643 | @smallexample | |
1644 | @group | |
1645 | (defun restore-match-data (data) | |
1646 | @c It is incorrect to split the first line of a doc string. | |
1647 | @c If there's a problem here, it should be solved in some other way. | |
1648 | "Restore the match data DATA unless the buffer is missing." | |
1649 | (catch 'foo | |
1650 | (let ((d data)) | |
1651 | @end group | |
1652 | (while d | |
1653 | (and (car d) | |
1654 | (null (marker-buffer (car d))) | |
1655 | @group | |
1656 | ;; @file{match-data} @r{buffer is deleted.} | |
1657 | (throw 'foo nil)) | |
1658 | (setq d (cdr d))) | |
1659 | (set-match-data data)))) | |
1660 | @end group | |
1661 | @end smallexample | |
1662 | @end ignore | |
1663 | ||
1664 | @node Searching and Case | |
1665 | @section Searching and Case | |
1666 | @cindex searching and case | |
1667 | ||
1668 | By default, searches in Emacs ignore the case of the text they are | |
1669 | searching through; if you specify searching for @samp{FOO}, then | |
f9f59935 RS |
1670 | @samp{Foo} or @samp{foo} is also considered a match. This applies to |
1671 | regular expressions, too; thus, @samp{[aB]} would match @samp{a} or | |
1672 | @samp{A} or @samp{b} or @samp{B}. | |
7015aca4 RS |
1673 | |
1674 | If you do not want this feature, set the variable | |
1675 | @code{case-fold-search} to @code{nil}. Then all letters must match | |
7fd1911a RS |
1676 | exactly, including case. This is a buffer-local variable; altering the |
1677 | variable affects only the current buffer. (@xref{Intro to | |
7015aca4 RS |
1678 | Buffer-Local}.) Alternatively, you may change the value of |
1679 | @code{default-case-fold-search}, which is the default value of | |
1680 | @code{case-fold-search} for buffers that do not override it. | |
1681 | ||
1682 | Note that the user-level incremental search feature handles case | |
1683 | distinctions differently. When given a lower case letter, it looks for | |
1684 | a match of either case, but when given an upper case letter, it looks | |
1685 | for an upper case letter only. But this has nothing to do with the | |
f9f59935 | 1686 | searching functions used in Lisp code. |
7015aca4 RS |
1687 | |
1688 | @defopt case-replace | |
bcb6b6b8 LT |
1689 | This variable determines whether the higher level replacement |
1690 | functions should preserve case. If the variable is @code{nil}, that | |
1691 | means to use the replacement text verbatim. A non-@code{nil} value | |
1692 | means to convert the case of the replacement text according to the | |
1693 | text being replaced. | |
7fd1911a | 1694 | |
8241495d RS |
1695 | This variable is used by passing it as an argument to the function |
1696 | @code{replace-match}. @xref{Replacing Match}. | |
7015aca4 RS |
1697 | @end defopt |
1698 | ||
1699 | @defopt case-fold-search | |
1700 | This buffer-local variable determines whether searches should ignore | |
1701 | case. If the variable is @code{nil} they do not ignore case; otherwise | |
1702 | they do ignore case. | |
1703 | @end defopt | |
1704 | ||
1705 | @defvar default-case-fold-search | |
1706 | The value of this variable is the default value for | |
1707 | @code{case-fold-search} in buffers that do not override it. This is the | |
1708 | same as @code{(default-value 'case-fold-search)}. | |
1709 | @end defvar | |
1710 | ||
1711 | @node Standard Regexps | |
1712 | @section Standard Regular Expressions Used in Editing | |
1713 | @cindex regexps used standardly in editing | |
1714 | @cindex standard regexps used in editing | |
1715 | ||
1716 | This section describes some variables that hold regular expressions | |
1717 | used for certain purposes in editing: | |
1718 | ||
1719 | @defvar page-delimiter | |
969fe9b5 RS |
1720 | This is the regular expression describing line-beginnings that separate |
1721 | pages. The default value is @code{"^\014"} (i.e., @code{"^^L"} or | |
1722 | @code{"^\C-l"}); this matches a line that starts with a formfeed | |
1723 | character. | |
7015aca4 RS |
1724 | @end defvar |
1725 | ||
22697dac KH |
1726 | The following two regular expressions should @emph{not} assume the |
1727 | match always starts at the beginning of a line; they should not use | |
1728 | @samp{^} to anchor the match. Most often, the paragraph commands do | |
1729 | check for a match only at the beginning of a line, which means that | |
bfe721d1 KH |
1730 | @samp{^} would be superfluous. When there is a nonzero left margin, |
1731 | they accept matches that start after the left margin. In that case, a | |
1732 | @samp{^} would be incorrect. However, a @samp{^} is harmless in modes | |
1733 | where a left margin is never used. | |
22697dac | 1734 | |
7015aca4 RS |
1735 | @defvar paragraph-separate |
1736 | This is the regular expression for recognizing the beginning of a line | |
1737 | that separates paragraphs. (If you change this, you may have to | |
7fd1911a | 1738 | change @code{paragraph-start} also.) The default value is |
22697dac KH |
1739 | @w{@code{"[@ \t\f]*$"}}, which matches a line that consists entirely of |
1740 | spaces, tabs, and form feeds (after its left margin). | |
7015aca4 RS |
1741 | @end defvar |
1742 | ||
1743 | @defvar paragraph-start | |
1744 | This is the regular expression for recognizing the beginning of a line | |
1745 | that starts @emph{or} separates paragraphs. The default value is | |
bcb6b6b8 LT |
1746 | @w{@code{"\f\\|[ \t]*$"}}, which matches a line containing only |
1747 | whitespace or starting with a form feed (after its left margin). | |
7015aca4 RS |
1748 | @end defvar |
1749 | ||
1750 | @defvar sentence-end | |
45fa30b2 LT |
1751 | If non-@code{nil}, the value should be a regular expression describing |
1752 | the end of a sentence, including the whitespace following the | |
1753 | sentence. (All paragraph boundaries also end sentences, regardless.) | |
1754 | ||
1755 | If the value is @code{nil}, the default, then the function | |
1756 | @code{sentence-end} has to construct the regexp. That is why you | |
1757 | should always call the function @code{sentence-end} to obtain the | |
1758 | regexp to be used to recognize the end of a sentence. | |
7015aca4 | 1759 | @end defvar |
ab5796a9 | 1760 | |
45fa30b2 LT |
1761 | @defun sentence-end |
1762 | This function returns the value of the variable @code{sentence-end}, | |
1763 | if non-@code{nil}. Otherwise it returns a default value based on the | |
1764 | values of the variables @code{sentence-end-double-space} | |
1765 | (@pxref{Definition of sentence-end-double-space}), | |
1766 | @code{sentence-end-without-period} and | |
1767 | @code{sentence-end-without-space}. | |
1768 | @end defun | |
1769 | ||
ab5796a9 MB |
1770 | @ignore |
1771 | arch-tag: c2573ca2-18aa-4839-93b8-924043ef831f | |
1772 | @end ignore |