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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
f9f59935 | 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998 Free Software Foundation, Inc. |
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4 | @c See the file elisp.texi for copying conditions. |
5 | @setfilename ../info/searching | |
f9f59935 | 6 | @node Searching and Matching, Syntax Tables, Non-ASCII Characters, Top |
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7 | @chapter Searching and Matching |
8 | @cindex searching | |
9 | ||
10 | GNU Emacs provides two ways to search through a buffer for specified | |
11 | text: exact string searches and regular expression searches. After a | |
12 | regular expression search, you can examine the @dfn{match data} to | |
13 | determine which text matched the whole regular expression or various | |
14 | portions of it. | |
15 | ||
16 | @menu | |
17 | * String Search:: Search for an exact match. | |
18 | * Regular Expressions:: Describing classes of strings. | |
19 | * Regexp Search:: Searching for a match for a regexp. | |
22697dac | 20 | * POSIX Regexps:: Searching POSIX-style for the longest match. |
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21 | * Search and Replace:: Internals of @code{query-replace}. |
22 | * Match Data:: Finding out which part of the text matched | |
23 | various parts of a regexp, after regexp search. | |
24 | * Searching and Case:: Case-independent or case-significant searching. | |
25 | * Standard Regexps:: Useful regexps for finding sentences, pages,... | |
26 | @end menu | |
27 | ||
28 | The @samp{skip-chars@dots{}} functions also perform a kind of searching. | |
29 | @xref{Skipping Characters}. | |
30 | ||
31 | @node String Search | |
32 | @section Searching for Strings | |
33 | @cindex string search | |
34 | ||
35 | These are the primitive functions for searching through the text in a | |
36 | buffer. They are meant for use in programs, but you may call them | |
37 | interactively. If you do so, they prompt for the search string; | |
38 | @var{limit} and @var{noerror} are set to @code{nil}, and @var{repeat} | |
39 | is set to 1. | |
40 | ||
f9f59935 RS |
41 | These search functions convert the search string to multibyte if the |
42 | buffer is multibyte; they convert the search string to unibyte if the | |
43 | buffer is unibyte. @xref{Text Representations}. | |
44 | ||
7015aca4 | 45 | @deffn Command search-forward string &optional limit noerror repeat |
f9f59935 | 46 | This function searches forward from point for an exact match for |
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47 | @var{string}. If successful, it sets point to the end of the occurrence |
48 | found, and returns the new value of point. If no match is found, the | |
49 | value and side effects depend on @var{noerror} (see below). | |
50 | @c Emacs 19 feature | |
51 | ||
f9f59935 | 52 | In the following example, point is initially at the beginning of the |
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53 | line. Then @code{(search-forward "fox")} moves point after the last |
54 | letter of @samp{fox}: | |
55 | ||
56 | @example | |
57 | @group | |
58 | ---------- Buffer: foo ---------- | |
59 | @point{}The quick brown fox jumped over the lazy dog. | |
60 | ---------- Buffer: foo ---------- | |
61 | @end group | |
62 | ||
63 | @group | |
64 | (search-forward "fox") | |
65 | @result{} 20 | |
66 | ||
67 | ---------- Buffer: foo ---------- | |
68 | The quick brown fox@point{} jumped over the lazy dog. | |
69 | ---------- Buffer: foo ---------- | |
70 | @end group | |
71 | @end example | |
72 | ||
f9f59935 | 73 | The argument @var{limit} specifies the upper bound to the search. (It |
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74 | must be a position in the current buffer.) No match extending after |
75 | that position is accepted. If @var{limit} is omitted or @code{nil}, it | |
76 | defaults to the end of the accessible portion of the buffer. | |
77 | ||
78 | @kindex search-failed | |
f9f59935 | 79 | What happens when the search fails depends on the value of |
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80 | @var{noerror}. If @var{noerror} is @code{nil}, a @code{search-failed} |
81 | error is signaled. If @var{noerror} is @code{t}, @code{search-forward} | |
82 | returns @code{nil} and does nothing. If @var{noerror} is neither | |
83 | @code{nil} nor @code{t}, then @code{search-forward} moves point to the | |
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84 | upper bound and returns @code{nil}. (It would be more consistent now to |
85 | return the new position of point in that case, but some existing | |
86 | programs may depend on a value of @code{nil}.) | |
7015aca4 | 87 | |
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88 | If @var{repeat} is supplied (it must be a positive number), then the |
89 | search is repeated that many times (each time starting at the end of the | |
90 | previous time's match). If these successive searches succeed, the | |
91 | function succeeds, moving point and returning its new value. Otherwise | |
92 | the search fails. | |
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93 | @end deffn |
94 | ||
95 | @deffn Command search-backward string &optional limit noerror repeat | |
96 | This function searches backward from point for @var{string}. It is | |
97 | just like @code{search-forward} except that it searches backwards and | |
98 | leaves point at the beginning of the match. | |
99 | @end deffn | |
100 | ||
101 | @deffn Command word-search-forward string &optional limit noerror repeat | |
102 | @cindex word search | |
103 | This function searches forward from point for a ``word'' match for | |
104 | @var{string}. If it finds a match, it sets point to the end of the | |
105 | match found, and returns the new value of point. | |
106 | @c Emacs 19 feature | |
107 | ||
108 | Word matching regards @var{string} as a sequence of words, disregarding | |
109 | punctuation that separates them. It searches the buffer for the same | |
110 | sequence of words. Each word must be distinct in the buffer (searching | |
111 | for the word @samp{ball} does not match the word @samp{balls}), but the | |
112 | details of punctuation and spacing are ignored (searching for @samp{ball | |
113 | boy} does match @samp{ball. Boy!}). | |
114 | ||
115 | In this example, point is initially at the beginning of the buffer; the | |
116 | search leaves it between the @samp{y} and the @samp{!}. | |
117 | ||
118 | @example | |
119 | @group | |
120 | ---------- Buffer: foo ---------- | |
121 | @point{}He said "Please! Find | |
122 | the ball boy!" | |
123 | ---------- Buffer: foo ---------- | |
124 | @end group | |
125 | ||
126 | @group | |
127 | (word-search-forward "Please find the ball, boy.") | |
128 | @result{} 35 | |
129 | ||
130 | ---------- Buffer: foo ---------- | |
131 | He said "Please! Find | |
132 | the ball boy@point{}!" | |
133 | ---------- Buffer: foo ---------- | |
134 | @end group | |
135 | @end example | |
136 | ||
137 | If @var{limit} is non-@code{nil} (it must be a position in the current | |
138 | buffer), then it is the upper bound to the search. The match found must | |
139 | not extend after that position. | |
140 | ||
141 | If @var{noerror} is @code{nil}, then @code{word-search-forward} signals | |
142 | an error if the search fails. If @var{noerror} is @code{t}, then it | |
143 | returns @code{nil} instead of signaling an error. If @var{noerror} is | |
144 | neither @code{nil} nor @code{t}, it moves point to @var{limit} (or the | |
145 | end of the buffer) and returns @code{nil}. | |
146 | ||
147 | If @var{repeat} is non-@code{nil}, then the search is repeated that many | |
148 | times. Point is positioned at the end of the last match. | |
149 | @end deffn | |
150 | ||
151 | @deffn Command word-search-backward string &optional limit noerror repeat | |
152 | This function searches backward from point for a word match to | |
153 | @var{string}. This function is just like @code{word-search-forward} | |
154 | except that it searches backward and normally leaves point at the | |
155 | beginning of the match. | |
156 | @end deffn | |
157 | ||
158 | @node Regular Expressions | |
159 | @section Regular Expressions | |
160 | @cindex regular expression | |
161 | @cindex regexp | |
162 | ||
163 | A @dfn{regular expression} (@dfn{regexp}, for short) is a pattern that | |
164 | denotes a (possibly infinite) set of strings. Searching for matches for | |
165 | a regexp is a very powerful operation. This section explains how to write | |
166 | regexps; the following section says how to search for them. | |
167 | ||
168 | @menu | |
169 | * Syntax of Regexps:: Rules for writing regular expressions. | |
170 | * Regexp Example:: Illustrates regular expression syntax. | |
171 | @end menu | |
172 | ||
173 | @node Syntax of Regexps | |
174 | @subsection Syntax of Regular Expressions | |
175 | ||
61cfa852 RS |
176 | Regular expressions have a syntax in which a few characters are |
177 | special constructs and the rest are @dfn{ordinary}. An ordinary | |
178 | character is a simple regular expression that matches that character and | |
179 | nothing else. The special characters are @samp{.}, @samp{*}, @samp{+}, | |
180 | @samp{?}, @samp{[}, @samp{]}, @samp{^}, @samp{$}, and @samp{\}; no new | |
181 | special characters will be defined in the future. Any other character | |
182 | appearing in a regular expression is ordinary, unless a @samp{\} | |
183 | precedes it. | |
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184 | |
185 | For example, @samp{f} is not a special character, so it is ordinary, and | |
186 | therefore @samp{f} is a regular expression that matches the string | |
187 | @samp{f} and no other string. (It does @emph{not} match the string | |
188 | @samp{ff}.) Likewise, @samp{o} is a regular expression that matches | |
189 | only @samp{o}.@refill | |
190 | ||
191 | Any two regular expressions @var{a} and @var{b} can be concatenated. The | |
61cfa852 | 192 | result is a regular expression that matches a string if @var{a} matches |
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193 | some amount of the beginning of that string and @var{b} matches the rest of |
194 | the string.@refill | |
195 | ||
196 | As a simple example, we can concatenate the regular expressions @samp{f} | |
197 | and @samp{o} to get the regular expression @samp{fo}, which matches only | |
198 | the string @samp{fo}. Still trivial. To do something more powerful, you | |
199 | need to use one of the special characters. Here is a list of them: | |
200 | ||
7dd3d99f | 201 | @need 800 |
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202 | @table @asis |
203 | @item @samp{.}@: @r{(Period)} | |
7015aca4 RS |
204 | @cindex @samp{.} in regexp |
205 | is a special character that matches any single character except a newline. | |
206 | Using concatenation, we can make regular expressions like @samp{a.b}, which | |
207 | matches any three-character string that begins with @samp{a} and ends with | |
208 | @samp{b}.@refill | |
209 | ||
969fe9b5 | 210 | @item @samp{*} |
7015aca4 | 211 | @cindex @samp{*} in regexp |
1cd71ce0 RS |
212 | is not a construct by itself; it is a postfix operator that means to |
213 | match the preceding regular expression repetitively as many times as | |
214 | possible. Thus, @samp{o*} matches any number of @samp{o}s (including no | |
215 | @samp{o}s). | |
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216 | |
217 | @samp{*} always applies to the @emph{smallest} possible preceding | |
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218 | expression. Thus, @samp{fo*} has a repeating @samp{o}, not a repeating |
219 | @samp{fo}. It matches @samp{f}, @samp{fo}, @samp{foo}, and so on. | |
7015aca4 | 220 | |
f9f59935 RS |
221 | The matcher processes a @samp{*} construct by matching, immediately, as |
222 | many repetitions as can be found. Then it continues with the rest of | |
223 | the pattern. If that fails, backtracking occurs, discarding some of the | |
224 | matches of the @samp{*}-modified construct in the hope that that will | |
225 | make it possible to match the rest of the pattern. For example, in | |
226 | matching @samp{ca*ar} against the string @samp{caaar}, the @samp{a*} | |
227 | first tries to match all three @samp{a}s; but the rest of the pattern is | |
7015aca4 | 228 | @samp{ar} and there is only @samp{r} left to match, so this try fails. |
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229 | The next alternative is for @samp{a*} to match only two @samp{a}s. With |
230 | this choice, the rest of the regexp matches successfully.@refill | |
7015aca4 | 231 | |
73031603 | 232 | Nested repetition operators can be extremely slow if they specify |
22697dac | 233 | backtracking loops. For example, it could take hours for the regular |
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234 | expression @samp{\(x+y*\)*a} to try to match the sequence |
235 | @samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz}, before it ultimately fails. | |
236 | The slowness is because Emacs must try each imaginable way of grouping | |
1911e6e5 | 237 | the 35 @samp{x}s before concluding that none of them can work. To make |
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238 | sure your regular expressions run fast, check nested repetitions |
239 | carefully. | |
73031603 | 240 | |
969fe9b5 | 241 | @item @samp{+} |
7015aca4 | 242 | @cindex @samp{+} in regexp |
1cd71ce0 RS |
243 | is a postfix operator, similar to @samp{*} except that it must match |
244 | the preceding expression at least once. So, for example, @samp{ca+r} | |
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245 | matches the strings @samp{car} and @samp{caaaar} but not the string |
246 | @samp{cr}, whereas @samp{ca*r} matches all three strings. | |
247 | ||
969fe9b5 | 248 | @item @samp{?} |
7015aca4 | 249 | @cindex @samp{?} in regexp |
f9f59935 | 250 | is a postfix operator, similar to @samp{*} except that it must match the |
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251 | preceding expression either once or not at all. For example, |
252 | @samp{ca?r} matches @samp{car} or @samp{cr}; nothing else. | |
7015aca4 | 253 | |
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254 | @item @samp{[ @dots{} ]} |
255 | @cindex character alternative (in regexp) | |
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256 | @cindex @samp{[} in regexp |
257 | @cindex @samp{]} in regexp | |
969fe9b5 RS |
258 | is a @dfn{character alternative}, which begins with @samp{[} and is |
259 | terminated by @samp{]}. In the simplest case, the characters between | |
260 | the two brackets are what this character alternative can match. | |
1cd71ce0 RS |
261 | |
262 | Thus, @samp{[ad]} matches either one @samp{a} or one @samp{d}, and | |
263 | @samp{[ad]*} matches any string composed of just @samp{a}s and @samp{d}s | |
264 | (including the empty string), from which it follows that @samp{c[ad]*r} | |
265 | matches @samp{cr}, @samp{car}, @samp{cdr}, @samp{caddaar}, etc. | |
266 | ||
969fe9b5 RS |
267 | You can also include character ranges in a character alternative, by |
268 | writing the starting and ending characters with a @samp{-} between them. | |
1911e6e5 | 269 | Thus, @samp{[a-z]} matches any lower-case @sc{ASCII} letter. Ranges may be |
1cd71ce0 | 270 | intermixed freely with individual characters, as in @samp{[a-z$%.]}, |
1911e6e5 | 271 | which matches any lower case @sc{ASCII} letter or @samp{$}, @samp{%} or |
1cd71ce0 | 272 | period. |
f9f59935 RS |
273 | |
274 | You cannot always match all non-@sc{ASCII} characters with the regular | |
275 | expression @samp{[\200-\377]}. This works when searching a unibyte | |
276 | buffer or string (@pxref{Text Representations}), but not in a multibyte | |
277 | buffer or string, because many non-@sc{ASCII} characters have codes | |
278 | above octal 0377. However, the regular expression @samp{[^\000-\177]} | |
279 | does match all non-@sc{ASCII} characters, in both multibyte and unibyte | |
280 | representations, because only the @sc{ASCII} characters are excluded. | |
281 | ||
282 | The beginning and end of a range must be in the same character set | |
1911e6e5 RS |
283 | (@pxref{Character Sets}). Thus, @samp{[a-\x8e0]} is invalid because |
284 | @samp{a} is in the @sc{ASCII} character set but the character 0x8e0 | |
285 | (@samp{a} with grave accent) is in the Emacs character set for Latin-1. | |
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286 | |
287 | Note that the usual regexp special characters are not special inside a | |
86494bd5 | 288 | character alternative. A completely different set of characters is |
969fe9b5 | 289 | special inside character alternatives: @samp{]}, @samp{-} and @samp{^}. |
1cd71ce0 | 290 | |
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291 | To include a @samp{]} in a character alternative, you must make it the |
292 | first character. For example, @samp{[]a]} matches @samp{]} or @samp{a}. | |
293 | To include a @samp{-}, write @samp{-} as the first or last character of | |
294 | the character alternative, or put it after a range. Thus, @samp{[]-]} | |
295 | matches both @samp{]} and @samp{-}. | |
7015aca4 | 296 | |
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297 | To include @samp{^} in a character alternative, put it anywhere but at |
298 | the beginning. | |
7015aca4 | 299 | |
969fe9b5 | 300 | @item @samp{[^ @dots{} ]} |
7015aca4 | 301 | @cindex @samp{^} in regexp |
969fe9b5 | 302 | @samp{[^} begins a @dfn{complemented character alternative}, which matches any |
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303 | character except the ones specified. Thus, @samp{[^a-z0-9A-Z]} matches |
304 | all characters @emph{except} letters and digits. | |
7015aca4 | 305 | |
969fe9b5 | 306 | @samp{^} is not special in a character alternative unless it is the first |
7015aca4 | 307 | character. The character following the @samp{^} is treated as if it |
1cd71ce0 | 308 | were first (in other words, @samp{-} and @samp{]} are not special there). |
7015aca4 | 309 | |
969fe9b5 | 310 | A complemented character alternative can match a newline, unless newline is |
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311 | mentioned as one of the characters not to match. This is in contrast to |
312 | the handling of regexps in programs such as @code{grep}. | |
7015aca4 | 313 | |
969fe9b5 | 314 | @item @samp{^} |
7015aca4 | 315 | @cindex beginning of line in regexp |
61cfa852 RS |
316 | is a special character that matches the empty string, but only at the |
317 | beginning of a line in the text being matched. Otherwise it fails to | |
318 | match anything. Thus, @samp{^foo} matches a @samp{foo} that occurs at | |
319 | the beginning of a line. | |
7015aca4 | 320 | |
61cfa852 RS |
321 | When matching a string instead of a buffer, @samp{^} matches at the |
322 | beginning of the string or after a newline character @samp{\n}. | |
7015aca4 | 323 | |
969fe9b5 | 324 | @item @samp{$} |
7015aca4 RS |
325 | @cindex @samp{$} in regexp |
326 | is similar to @samp{^} but matches only at the end of a line. Thus, | |
327 | @samp{x+$} matches a string of one @samp{x} or more at the end of a line. | |
328 | ||
61cfa852 RS |
329 | When matching a string instead of a buffer, @samp{$} matches at the end |
330 | of the string or before a newline character @samp{\n}. | |
7015aca4 | 331 | |
969fe9b5 | 332 | @item @samp{\} |
7015aca4 RS |
333 | @cindex @samp{\} in regexp |
334 | has two functions: it quotes the special characters (including | |
335 | @samp{\}), and it introduces additional special constructs. | |
336 | ||
337 | Because @samp{\} quotes special characters, @samp{\$} is a regular | |
61cfa852 RS |
338 | expression that matches only @samp{$}, and @samp{\[} is a regular |
339 | expression that matches only @samp{[}, and so on. | |
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340 | |
341 | Note that @samp{\} also has special meaning in the read syntax of Lisp | |
342 | strings (@pxref{String Type}), and must be quoted with @samp{\}. For | |
343 | example, the regular expression that matches the @samp{\} character is | |
344 | @samp{\\}. To write a Lisp string that contains the characters | |
345 | @samp{\\}, Lisp syntax requires you to quote each @samp{\} with another | |
346 | @samp{\}. Therefore, the read syntax for a regular expression matching | |
347 | @samp{\} is @code{"\\\\"}.@refill | |
348 | @end table | |
349 | ||
b22f3a19 | 350 | @strong{Please note:} For historical compatibility, special characters |
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351 | are treated as ordinary ones if they are in contexts where their special |
352 | meanings make no sense. For example, @samp{*foo} treats @samp{*} as | |
353 | ordinary since there is no preceding expression on which the @samp{*} | |
61cfa852 RS |
354 | can act. It is poor practice to depend on this behavior; quote the |
355 | special character anyway, regardless of where it appears.@refill | |
7015aca4 | 356 | |
a9f0a989 RS |
357 | For the most part, @samp{\} followed by any character matches only that |
358 | character. However, there are several exceptions: two-character | |
359 | sequences starting with @samp{\} which have special meanings. (The | |
360 | second character in such a sequence is always ordinary when used on its | |
361 | own.) Here is a table of @samp{\} constructs. | |
7015aca4 | 362 | |
969fe9b5 | 363 | @table @samp |
7015aca4 RS |
364 | @item \| |
365 | @cindex @samp{|} in regexp | |
366 | @cindex regexp alternative | |
367 | specifies an alternative. | |
368 | Two regular expressions @var{a} and @var{b} with @samp{\|} in | |
369 | between form an expression that matches anything that either @var{a} or | |
370 | @var{b} matches.@refill | |
371 | ||
372 | Thus, @samp{foo\|bar} matches either @samp{foo} or @samp{bar} | |
373 | but no other string.@refill | |
374 | ||
375 | @samp{\|} applies to the largest possible surrounding expressions. Only a | |
376 | surrounding @samp{\( @dots{} \)} grouping can limit the grouping power of | |
377 | @samp{\|}.@refill | |
378 | ||
379 | Full backtracking capability exists to handle multiple uses of @samp{\|}. | |
380 | ||
381 | @item \( @dots{} \) | |
382 | @cindex @samp{(} in regexp | |
383 | @cindex @samp{)} in regexp | |
384 | @cindex regexp grouping | |
385 | is a grouping construct that serves three purposes: | |
386 | ||
387 | @enumerate | |
388 | @item | |
9e2b495b RS |
389 | To enclose a set of @samp{\|} alternatives for other operations. Thus, |
390 | the regular expression @samp{\(foo\|bar\)x} matches either @samp{foox} | |
391 | or @samp{barx}. | |
7015aca4 RS |
392 | |
393 | @item | |
1cd71ce0 RS |
394 | To enclose a complicated expression for the postfix operators @samp{*}, |
395 | @samp{+} and @samp{?} to operate on. Thus, @samp{ba\(na\)*} matches | |
a9f0a989 RS |
396 | @samp{ba}, @samp{bana}, @samp{banana}, @samp{bananana}, etc., with any |
397 | number (zero or more) of @samp{na} strings. | |
7015aca4 RS |
398 | |
399 | @item | |
400 | To record a matched substring for future reference. | |
401 | @end enumerate | |
402 | ||
403 | This last application is not a consequence of the idea of a | |
61cfa852 | 404 | parenthetical grouping; it is a separate feature that happens to be |
7015aca4 RS |
405 | assigned as a second meaning to the same @samp{\( @dots{} \)} construct |
406 | because there is no conflict in practice between the two meanings. | |
407 | Here is an explanation of this feature: | |
408 | ||
409 | @item \@var{digit} | |
61cfa852 | 410 | matches the same text that matched the @var{digit}th occurrence of a |
7015aca4 RS |
411 | @samp{\( @dots{} \)} construct. |
412 | ||
1cd71ce0 | 413 | In other words, after the end of a @samp{\( @dots{} \)} construct, the |
7015aca4 RS |
414 | matcher remembers the beginning and end of the text matched by that |
415 | construct. Then, later on in the regular expression, you can use | |
416 | @samp{\} followed by @var{digit} to match that same text, whatever it | |
417 | may have been. | |
418 | ||
419 | The strings matching the first nine @samp{\( @dots{} \)} constructs | |
420 | appearing in a regular expression are assigned numbers 1 through 9 in | |
421 | the order that the open parentheses appear in the regular expression. | |
422 | So you can use @samp{\1} through @samp{\9} to refer to the text matched | |
423 | by the corresponding @samp{\( @dots{} \)} constructs. | |
424 | ||
425 | For example, @samp{\(.*\)\1} matches any newline-free string that is | |
426 | composed of two identical halves. The @samp{\(.*\)} matches the first | |
427 | half, which may be anything, but the @samp{\1} that follows must match | |
428 | the same exact text. | |
429 | ||
430 | @item \w | |
431 | @cindex @samp{\w} in regexp | |
432 | matches any word-constituent character. The editor syntax table | |
433 | determines which characters these are. @xref{Syntax Tables}. | |
434 | ||
435 | @item \W | |
436 | @cindex @samp{\W} in regexp | |
61cfa852 | 437 | matches any character that is not a word constituent. |
7015aca4 RS |
438 | |
439 | @item \s@var{code} | |
440 | @cindex @samp{\s} in regexp | |
441 | matches any character whose syntax is @var{code}. Here @var{code} is a | |
61cfa852 | 442 | character that represents a syntax code: thus, @samp{w} for word |
7015aca4 | 443 | constituent, @samp{-} for whitespace, @samp{(} for open parenthesis, |
f9f59935 RS |
444 | etc. To represent whitespace syntax, use either @samp{-} or a space |
445 | character. @xref{Syntax Class Table}, for a list of syntax codes and | |
446 | the characters that stand for them. | |
7015aca4 RS |
447 | |
448 | @item \S@var{code} | |
449 | @cindex @samp{\S} in regexp | |
450 | matches any character whose syntax is not @var{code}. | |
451 | @end table | |
452 | ||
61cfa852 | 453 | The following regular expression constructs match the empty string---that is, |
7015aca4 RS |
454 | they don't use up any characters---but whether they match depends on the |
455 | context. | |
456 | ||
969fe9b5 | 457 | @table @samp |
7015aca4 RS |
458 | @item \` |
459 | @cindex @samp{\`} in regexp | |
460 | matches the empty string, but only at the beginning | |
461 | of the buffer or string being matched against. | |
462 | ||
463 | @item \' | |
464 | @cindex @samp{\'} in regexp | |
465 | matches the empty string, but only at the end of | |
466 | the buffer or string being matched against. | |
467 | ||
468 | @item \= | |
469 | @cindex @samp{\=} in regexp | |
470 | matches the empty string, but only at point. | |
471 | (This construct is not defined when matching against a string.) | |
472 | ||
473 | @item \b | |
474 | @cindex @samp{\b} in regexp | |
475 | matches the empty string, but only at the beginning or | |
476 | end of a word. Thus, @samp{\bfoo\b} matches any occurrence of | |
477 | @samp{foo} as a separate word. @samp{\bballs?\b} matches | |
478 | @samp{ball} or @samp{balls} as a separate word.@refill | |
479 | ||
1cd71ce0 RS |
480 | @samp{\b} matches at the beginning or end of the buffer |
481 | regardless of what text appears next to it. | |
482 | ||
7015aca4 RS |
483 | @item \B |
484 | @cindex @samp{\B} in regexp | |
485 | matches the empty string, but @emph{not} at the beginning or | |
486 | end of a word. | |
487 | ||
488 | @item \< | |
489 | @cindex @samp{\<} in regexp | |
490 | matches the empty string, but only at the beginning of a word. | |
1cd71ce0 RS |
491 | @samp{\<} matches at the beginning of the buffer only if a |
492 | word-constituent character follows. | |
7015aca4 RS |
493 | |
494 | @item \> | |
495 | @cindex @samp{\>} in regexp | |
1cd71ce0 RS |
496 | matches the empty string, but only at the end of a word. @samp{\>} |
497 | matches at the end of the buffer only if the contents end with a | |
498 | word-constituent character. | |
7015aca4 RS |
499 | @end table |
500 | ||
501 | @kindex invalid-regexp | |
502 | Not every string is a valid regular expression. For example, a string | |
503 | with unbalanced square brackets is invalid (with a few exceptions, such | |
61cfa852 | 504 | as @samp{[]]}), and so is a string that ends with a single @samp{\}. If |
7015aca4 RS |
505 | an invalid regular expression is passed to any of the search functions, |
506 | an @code{invalid-regexp} error is signaled. | |
507 | ||
508 | @defun regexp-quote string | |
509 | This function returns a regular expression string that matches exactly | |
510 | @var{string} and nothing else. This allows you to request an exact | |
511 | string match when calling a function that wants a regular expression. | |
512 | ||
513 | @example | |
514 | @group | |
515 | (regexp-quote "^The cat$") | |
516 | @result{} "\\^The cat\\$" | |
517 | @end group | |
518 | @end example | |
519 | ||
520 | One use of @code{regexp-quote} is to combine an exact string match with | |
521 | context described as a regular expression. For example, this searches | |
969fe9b5 | 522 | for the string that is the value of @var{string}, surrounded by |
7015aca4 RS |
523 | whitespace: |
524 | ||
525 | @example | |
526 | @group | |
527 | (re-search-forward | |
61cfa852 | 528 | (concat "\\s-" (regexp-quote string) "\\s-")) |
7015aca4 RS |
529 | @end group |
530 | @end example | |
531 | @end defun | |
532 | ||
f9f59935 | 533 | @defun regexp-opt strings &optional paren |
a9f0a989 | 534 | @tindex regexp-opt |
f9f59935 RS |
535 | This function returns an efficient regular expression that will match |
536 | any of the strings @var{strings}. This is useful when you need to make | |
537 | matching or searching as fast as possible---for example, for Font Lock | |
538 | mode. | |
539 | ||
540 | If the optional argument @var{paren} is non-@code{nil}, then the | |
541 | returned regular expression is always enclosed by at least one | |
542 | parentheses-grouping construct. | |
543 | ||
544 | This simplified definition of @code{regexp-opt} produces a | |
545 | regular expression which is equivalent to the actual value | |
546 | (but not as efficient): | |
547 | ||
548 | @example | |
549 | (defun regexp-opt (strings paren) | |
550 | (let ((open-paren (if paren "\\(" "")) | |
551 | (close-paren (if paren "\\)" ""))) | |
552 | (concat open-paren | |
553 | (mapconcat 'regexp-quote strings "\\|") | |
554 | close-paren))) | |
555 | @end example | |
556 | @end defun | |
557 | ||
f9f59935 | 558 | @defun regexp-opt-depth regexp |
a9f0a989 | 559 | @tindex regexp-opt-depth |
f9f59935 | 560 | This function returns the total number of grouping constructs |
969fe9b5 | 561 | (parenthesized expressions) in @var{regexp}. |
f9f59935 RS |
562 | @end defun |
563 | ||
7015aca4 RS |
564 | @node Regexp Example |
565 | @comment node-name, next, previous, up | |
566 | @subsection Complex Regexp Example | |
567 | ||
568 | Here is a complicated regexp, used by Emacs to recognize the end of a | |
569 | sentence together with any whitespace that follows. It is the value of | |
570 | the variable @code{sentence-end}. | |
571 | ||
572 | First, we show the regexp as a string in Lisp syntax to distinguish | |
573 | spaces from tab characters. The string constant begins and ends with a | |
574 | double-quote. @samp{\"} stands for a double-quote as part of the | |
575 | string, @samp{\\} for a backslash as part of the string, @samp{\t} for a | |
576 | tab and @samp{\n} for a newline. | |
577 | ||
578 | @example | |
579 | "[.?!][]\"')@}]*\\($\\| $\\|\t\\| \\)[ \t\n]*" | |
580 | @end example | |
581 | ||
969fe9b5 RS |
582 | @noindent |
583 | In contrast, if you evaluate the variable @code{sentence-end}, you | |
7015aca4 RS |
584 | will see the following: |
585 | ||
586 | @example | |
587 | @group | |
588 | sentence-end | |
969fe9b5 | 589 | @result{} "[.?!][]\"')@}]*\\($\\| $\\| \\| \\)[ |
7015aca4 RS |
590 | ]*" |
591 | @end group | |
592 | @end example | |
593 | ||
594 | @noindent | |
595 | In this output, tab and newline appear as themselves. | |
596 | ||
597 | This regular expression contains four parts in succession and can be | |
598 | deciphered as follows: | |
599 | ||
600 | @table @code | |
601 | @item [.?!] | |
969fe9b5 RS |
602 | The first part of the pattern is a character alternative that matches |
603 | any one of three characters: period, question mark, and exclamation | |
604 | mark. The match must begin with one of these three characters. | |
7015aca4 RS |
605 | |
606 | @item []\"')@}]* | |
607 | The second part of the pattern matches any closing braces and quotation | |
608 | marks, zero or more of them, that may follow the period, question mark | |
609 | or exclamation mark. The @code{\"} is Lisp syntax for a double-quote in | |
610 | a string. The @samp{*} at the end indicates that the immediately | |
969fe9b5 | 611 | preceding regular expression (a character alternative, in this case) may be |
7015aca4 RS |
612 | repeated zero or more times. |
613 | ||
7fd1911a | 614 | @item \\($\\|@ $\\|\t\\|@ @ \\) |
7015aca4 | 615 | The third part of the pattern matches the whitespace that follows the |
f9f59935 RS |
616 | end of a sentence: the end of a line (optionally with a space), or a |
617 | tab, or two spaces. The double backslashes mark the parentheses and | |
618 | vertical bars as regular expression syntax; the parentheses delimit a | |
619 | group and the vertical bars separate alternatives. The dollar sign is | |
620 | used to match the end of a line. | |
7015aca4 RS |
621 | |
622 | @item [ \t\n]* | |
623 | Finally, the last part of the pattern matches any additional whitespace | |
624 | beyond the minimum needed to end a sentence. | |
625 | @end table | |
626 | ||
627 | @node Regexp Search | |
628 | @section Regular Expression Searching | |
629 | @cindex regular expression searching | |
630 | @cindex regexp searching | |
631 | @cindex searching for regexp | |
632 | ||
969fe9b5 RS |
633 | In GNU Emacs, you can search for the next match for a regular |
634 | expression either incrementally or not. For incremental search | |
635 | commands, see @ref{Regexp Search, , Regular Expression Search, emacs, | |
636 | The GNU Emacs Manual}. Here we describe only the search functions | |
637 | useful in programs. The principal one is @code{re-search-forward}. | |
7015aca4 | 638 | |
f9f59935 RS |
639 | These search functions convert the regular expression to multibyte if |
640 | the buffer is multibyte; they convert the regular expression to unibyte | |
641 | if the buffer is unibyte. @xref{Text Representations}. | |
642 | ||
7015aca4 RS |
643 | @deffn Command re-search-forward regexp &optional limit noerror repeat |
644 | This function searches forward in the current buffer for a string of | |
645 | text that is matched by the regular expression @var{regexp}. The | |
646 | function skips over any amount of text that is not matched by | |
647 | @var{regexp}, and leaves point at the end of the first match found. | |
648 | It returns the new value of point. | |
649 | ||
650 | If @var{limit} is non-@code{nil} (it must be a position in the current | |
651 | buffer), then it is the upper bound to the search. No match extending | |
652 | after that position is accepted. | |
653 | ||
f9f59935 RS |
654 | If @var{repeat} is supplied (it must be a positive number), then the |
655 | search is repeated that many times (each time starting at the end of the | |
656 | previous time's match). If all these successive searches succeed, the | |
657 | function succeeds, moving point and returning its new value. Otherwise | |
658 | the function fails. | |
659 | ||
660 | What happens when the function fails depends on the value of | |
7015aca4 RS |
661 | @var{noerror}. If @var{noerror} is @code{nil}, a @code{search-failed} |
662 | error is signaled. If @var{noerror} is @code{t}, | |
663 | @code{re-search-forward} does nothing and returns @code{nil}. If | |
664 | @var{noerror} is neither @code{nil} nor @code{t}, then | |
665 | @code{re-search-forward} moves point to @var{limit} (or the end of the | |
666 | buffer) and returns @code{nil}. | |
667 | ||
7015aca4 RS |
668 | In the following example, point is initially before the @samp{T}. |
669 | Evaluating the search call moves point to the end of that line (between | |
670 | the @samp{t} of @samp{hat} and the newline). | |
671 | ||
672 | @example | |
673 | @group | |
674 | ---------- Buffer: foo ---------- | |
675 | I read "@point{}The cat in the hat | |
676 | comes back" twice. | |
677 | ---------- Buffer: foo ---------- | |
678 | @end group | |
679 | ||
680 | @group | |
681 | (re-search-forward "[a-z]+" nil t 5) | |
682 | @result{} 27 | |
683 | ||
684 | ---------- Buffer: foo ---------- | |
685 | I read "The cat in the hat@point{} | |
686 | comes back" twice. | |
687 | ---------- Buffer: foo ---------- | |
688 | @end group | |
689 | @end example | |
690 | @end deffn | |
691 | ||
692 | @deffn Command re-search-backward regexp &optional limit noerror repeat | |
693 | This function searches backward in the current buffer for a string of | |
694 | text that is matched by the regular expression @var{regexp}, leaving | |
695 | point at the beginning of the first text found. | |
696 | ||
7fd1911a RS |
697 | This function is analogous to @code{re-search-forward}, but they are not |
698 | simple mirror images. @code{re-search-forward} finds the match whose | |
699 | beginning is as close as possible to the starting point. If | |
700 | @code{re-search-backward} were a perfect mirror image, it would find the | |
701 | match whose end is as close as possible. However, in fact it finds the | |
3f63de1e | 702 | match whose beginning is as close as possible. The reason for this is that |
7fd1911a RS |
703 | matching a regular expression at a given spot always works from |
704 | beginning to end, and starts at a specified beginning position. | |
7015aca4 RS |
705 | |
706 | A true mirror-image of @code{re-search-forward} would require a special | |
969fe9b5 RS |
707 | feature for matching regular expressions from end to beginning. It's |
708 | not worth the trouble of implementing that. | |
7015aca4 RS |
709 | @end deffn |
710 | ||
711 | @defun string-match regexp string &optional start | |
712 | This function returns the index of the start of the first match for | |
713 | the regular expression @var{regexp} in @var{string}, or @code{nil} if | |
714 | there is no match. If @var{start} is non-@code{nil}, the search starts | |
715 | at that index in @var{string}. | |
716 | ||
717 | For example, | |
718 | ||
719 | @example | |
720 | @group | |
721 | (string-match | |
722 | "quick" "The quick brown fox jumped quickly.") | |
723 | @result{} 4 | |
724 | @end group | |
725 | @group | |
726 | (string-match | |
727 | "quick" "The quick brown fox jumped quickly." 8) | |
728 | @result{} 27 | |
729 | @end group | |
730 | @end example | |
731 | ||
732 | @noindent | |
733 | The index of the first character of the | |
734 | string is 0, the index of the second character is 1, and so on. | |
735 | ||
736 | After this function returns, the index of the first character beyond | |
737 | the match is available as @code{(match-end 0)}. @xref{Match Data}. | |
738 | ||
739 | @example | |
740 | @group | |
741 | (string-match | |
742 | "quick" "The quick brown fox jumped quickly." 8) | |
743 | @result{} 27 | |
744 | @end group | |
745 | ||
746 | @group | |
747 | (match-end 0) | |
748 | @result{} 32 | |
749 | @end group | |
750 | @end example | |
751 | @end defun | |
752 | ||
753 | @defun looking-at regexp | |
754 | This function determines whether the text in the current buffer directly | |
755 | following point matches the regular expression @var{regexp}. ``Directly | |
756 | following'' means precisely that: the search is ``anchored'' and it can | |
757 | succeed only starting with the first character following point. The | |
758 | result is @code{t} if so, @code{nil} otherwise. | |
759 | ||
760 | This function does not move point, but it updates the match data, which | |
761 | you can access using @code{match-beginning} and @code{match-end}. | |
762 | @xref{Match Data}. | |
763 | ||
764 | In this example, point is located directly before the @samp{T}. If it | |
765 | were anywhere else, the result would be @code{nil}. | |
766 | ||
767 | @example | |
768 | @group | |
769 | ---------- Buffer: foo ---------- | |
770 | I read "@point{}The cat in the hat | |
771 | comes back" twice. | |
772 | ---------- Buffer: foo ---------- | |
773 | ||
774 | (looking-at "The cat in the hat$") | |
775 | @result{} t | |
776 | @end group | |
777 | @end example | |
778 | @end defun | |
779 | ||
22697dac KH |
780 | @node POSIX Regexps |
781 | @section POSIX Regular Expression Searching | |
782 | ||
783 | The usual regular expression functions do backtracking when necessary | |
784 | to handle the @samp{\|} and repetition constructs, but they continue | |
785 | this only until they find @emph{some} match. Then they succeed and | |
786 | report the first match found. | |
787 | ||
788 | This section describes alternative search functions which perform the | |
789 | full backtracking specified by the POSIX standard for regular expression | |
790 | matching. They continue backtracking until they have tried all | |
791 | possibilities and found all matches, so they can report the longest | |
792 | match, as required by POSIX. This is much slower, so use these | |
793 | functions only when you really need the longest match. | |
794 | ||
22697dac KH |
795 | @defun posix-search-forward regexp &optional limit noerror repeat |
796 | This is like @code{re-search-forward} except that it performs the full | |
797 | backtracking specified by the POSIX standard for regular expression | |
798 | matching. | |
799 | @end defun | |
800 | ||
801 | @defun posix-search-backward regexp &optional limit noerror repeat | |
802 | This is like @code{re-search-backward} except that it performs the full | |
803 | backtracking specified by the POSIX standard for regular expression | |
804 | matching. | |
805 | @end defun | |
806 | ||
807 | @defun posix-looking-at regexp | |
808 | This is like @code{looking-at} except that it performs the full | |
809 | backtracking specified by the POSIX standard for regular expression | |
810 | matching. | |
811 | @end defun | |
812 | ||
813 | @defun posix-string-match regexp string &optional start | |
814 | This is like @code{string-match} except that it performs the full | |
815 | backtracking specified by the POSIX standard for regular expression | |
816 | matching. | |
817 | @end defun | |
818 | ||
7015aca4 RS |
819 | @ignore |
820 | @deffn Command delete-matching-lines regexp | |
821 | This function is identical to @code{delete-non-matching-lines}, save | |
822 | that it deletes what @code{delete-non-matching-lines} keeps. | |
823 | ||
824 | In the example below, point is located on the first line of text. | |
825 | ||
826 | @example | |
827 | @group | |
828 | ---------- Buffer: foo ---------- | |
829 | We hold these truths | |
830 | to be self-evident, | |
831 | that all men are created | |
832 | equal, and that they are | |
833 | ---------- Buffer: foo ---------- | |
834 | @end group | |
835 | ||
836 | @group | |
837 | (delete-matching-lines "the") | |
838 | @result{} nil | |
839 | ||
840 | ---------- Buffer: foo ---------- | |
841 | to be self-evident, | |
842 | that all men are created | |
843 | ---------- Buffer: foo ---------- | |
844 | @end group | |
845 | @end example | |
846 | @end deffn | |
847 | ||
848 | @deffn Command flush-lines regexp | |
849 | This function is the same as @code{delete-matching-lines}. | |
850 | @end deffn | |
851 | ||
852 | @defun delete-non-matching-lines regexp | |
853 | This function deletes all lines following point which don't | |
854 | contain a match for the regular expression @var{regexp}. | |
855 | @end defun | |
856 | ||
857 | @deffn Command keep-lines regexp | |
858 | This function is the same as @code{delete-non-matching-lines}. | |
859 | @end deffn | |
860 | ||
861 | @deffn Command how-many regexp | |
862 | This function counts the number of matches for @var{regexp} there are in | |
863 | the current buffer following point. It prints this number in | |
864 | the echo area, returning the string printed. | |
865 | @end deffn | |
866 | ||
867 | @deffn Command count-matches regexp | |
868 | This function is a synonym of @code{how-many}. | |
869 | @end deffn | |
870 | ||
871 | @deffn Command list-matching-lines regexp nlines | |
872 | This function is a synonym of @code{occur}. | |
873 | Show all lines following point containing a match for @var{regexp}. | |
874 | Display each line with @var{nlines} lines before and after, | |
875 | or @code{-}@var{nlines} before if @var{nlines} is negative. | |
876 | @var{nlines} defaults to @code{list-matching-lines-default-context-lines}. | |
877 | Interactively it is the prefix arg. | |
878 | ||
879 | The lines are shown in a buffer named @samp{*Occur*}. | |
880 | It serves as a menu to find any of the occurrences in this buffer. | |
86494bd5 | 881 | @kbd{C-h m} (@code{describe-mode}) in that buffer gives help. |
7015aca4 RS |
882 | @end deffn |
883 | ||
884 | @defopt list-matching-lines-default-context-lines | |
885 | Default value is 0. | |
886 | Default number of context lines to include around a @code{list-matching-lines} | |
887 | match. A negative number means to include that many lines before the match. | |
888 | A positive number means to include that many lines both before and after. | |
889 | @end defopt | |
890 | @end ignore | |
891 | ||
892 | @node Search and Replace | |
893 | @section Search and Replace | |
894 | @cindex replacement | |
895 | ||
896 | @defun perform-replace from-string replacements query-flag regexp-flag delimited-flag &optional repeat-count map | |
897 | This function is the guts of @code{query-replace} and related commands. | |
898 | It searches for occurrences of @var{from-string} and replaces some or | |
899 | all of them. If @var{query-flag} is @code{nil}, it replaces all | |
900 | occurrences; otherwise, it asks the user what to do about each one. | |
901 | ||
902 | If @var{regexp-flag} is non-@code{nil}, then @var{from-string} is | |
903 | considered a regular expression; otherwise, it must match literally. If | |
904 | @var{delimited-flag} is non-@code{nil}, then only replacements | |
905 | surrounded by word boundaries are considered. | |
906 | ||
907 | The argument @var{replacements} specifies what to replace occurrences | |
908 | with. If it is a string, that string is used. It can also be a list of | |
909 | strings, to be used in cyclic order. | |
910 | ||
bda144f4 MW |
911 | If @var{repeat-count} is non-@code{nil}, it should be an integer. Then |
912 | it specifies how many times to use each of the strings in the | |
913 | @var{replacements} list before advancing cyclicly to the next one. | |
7015aca4 RS |
914 | |
915 | Normally, the keymap @code{query-replace-map} defines the possible user | |
7fd1911a RS |
916 | responses for queries. The argument @var{map}, if non-@code{nil}, is a |
917 | keymap to use instead of @code{query-replace-map}. | |
7015aca4 RS |
918 | @end defun |
919 | ||
920 | @defvar query-replace-map | |
921 | This variable holds a special keymap that defines the valid user | |
922 | responses for @code{query-replace} and related functions, as well as | |
923 | @code{y-or-n-p} and @code{map-y-or-n-p}. It is unusual in two ways: | |
924 | ||
925 | @itemize @bullet | |
926 | @item | |
927 | The ``key bindings'' are not commands, just symbols that are meaningful | |
928 | to the functions that use this map. | |
929 | ||
930 | @item | |
f9f59935 RS |
931 | Prefix keys are not supported; each key binding must be for a |
932 | single-event key sequence. This is because the functions don't use | |
933 | @code{read-key-sequence} to get the input; instead, they read a single | |
934 | event and look it up ``by hand.'' | |
7015aca4 RS |
935 | @end itemize |
936 | @end defvar | |
937 | ||
938 | Here are the meaningful ``bindings'' for @code{query-replace-map}. | |
939 | Several of them are meaningful only for @code{query-replace} and | |
940 | friends. | |
941 | ||
942 | @table @code | |
943 | @item act | |
944 | Do take the action being considered---in other words, ``yes.'' | |
945 | ||
946 | @item skip | |
947 | Do not take action for this question---in other words, ``no.'' | |
948 | ||
949 | @item exit | |
7fd1911a RS |
950 | Answer this question ``no,'' and give up on the entire series of |
951 | questions, assuming that the answers will be ``no.'' | |
7015aca4 RS |
952 | |
953 | @item act-and-exit | |
7fd1911a RS |
954 | Answer this question ``yes,'' and give up on the entire series of |
955 | questions, assuming that subsequent answers will be ``no.'' | |
7015aca4 RS |
956 | |
957 | @item act-and-show | |
958 | Answer this question ``yes,'' but show the results---don't advance yet | |
959 | to the next question. | |
960 | ||
961 | @item automatic | |
962 | Answer this question and all subsequent questions in the series with | |
963 | ``yes,'' without further user interaction. | |
964 | ||
965 | @item backup | |
966 | Move back to the previous place that a question was asked about. | |
967 | ||
968 | @item edit | |
969 | Enter a recursive edit to deal with this question---instead of any | |
970 | other action that would normally be taken. | |
971 | ||
972 | @item delete-and-edit | |
973 | Delete the text being considered, then enter a recursive edit to replace | |
974 | it. | |
975 | ||
976 | @item recenter | |
977 | Redisplay and center the window, then ask the same question again. | |
978 | ||
979 | @item quit | |
980 | Perform a quit right away. Only @code{y-or-n-p} and related functions | |
981 | use this answer. | |
982 | ||
983 | @item help | |
984 | Display some help, then ask again. | |
985 | @end table | |
986 | ||
987 | @node Match Data | |
988 | @section The Match Data | |
989 | @cindex match data | |
990 | ||
3f63de1e | 991 | Emacs keeps track of the start and end positions of the segments of |
7015aca4 RS |
992 | text found during a regular expression search. This means, for example, |
993 | that you can search for a complex pattern, such as a date in an Rmail | |
994 | message, and then extract parts of the match under control of the | |
995 | pattern. | |
996 | ||
997 | Because the match data normally describe the most recent search only, | |
998 | you must be careful not to do another search inadvertently between the | |
999 | search you wish to refer back to and the use of the match data. If you | |
1000 | can't avoid another intervening search, you must save and restore the | |
1001 | match data around it, to prevent it from being overwritten. | |
1002 | ||
1003 | @menu | |
969fe9b5 | 1004 | * Replacing Match:: Replacing a substring that was matched. |
7015aca4 RS |
1005 | * Simple Match Data:: Accessing single items of match data, |
1006 | such as where a particular subexpression started. | |
7015aca4 RS |
1007 | * Entire Match Data:: Accessing the entire match data at once, as a list. |
1008 | * Saving Match Data:: Saving and restoring the match data. | |
1009 | @end menu | |
1010 | ||
969fe9b5 RS |
1011 | @node Replacing Match |
1012 | @subsection Replacing the Text That Matched | |
1013 | ||
1014 | This function replaces the text matched by the last search with | |
1015 | @var{replacement}. | |
1016 | ||
1017 | @cindex case in replacements | |
1018 | @defun replace-match replacement &optional fixedcase literal string subexp | |
1019 | This function replaces the text in the buffer (or in @var{string}) that | |
1020 | was matched by the last search. It replaces that text with | |
1021 | @var{replacement}. | |
1022 | ||
1023 | If you did the last search in a buffer, you should specify @code{nil} | |
1024 | for @var{string}. Then @code{replace-match} does the replacement by | |
1025 | editing the buffer; it leaves point at the end of the replacement text, | |
1026 | and returns @code{t}. | |
1027 | ||
1028 | If you did the search in a string, pass the same string as @var{string}. | |
1029 | Then @code{replace-match} does the replacement by constructing and | |
1030 | returning a new string. | |
1031 | ||
1032 | If @var{fixedcase} is non-@code{nil}, then the case of the replacement | |
1033 | text is not changed; otherwise, the replacement text is converted to a | |
1034 | different case depending upon the capitalization of the text to be | |
1035 | replaced. If the original text is all upper case, the replacement text | |
1036 | is converted to upper case. If the first word of the original text is | |
1037 | capitalized, then the first word of the replacement text is capitalized. | |
1038 | If the original text contains just one word, and that word is a capital | |
1039 | letter, @code{replace-match} considers this a capitalized first word | |
1040 | rather than all upper case. | |
1041 | ||
1042 | If @code{case-replace} is @code{nil}, then case conversion is not done, | |
1043 | regardless of the value of @var{fixed-case}. @xref{Searching and Case}. | |
1044 | ||
1045 | If @var{literal} is non-@code{nil}, then @var{replacement} is inserted | |
1046 | exactly as it is, the only alterations being case changes as needed. | |
1047 | If it is @code{nil} (the default), then the character @samp{\} is treated | |
1048 | specially. If a @samp{\} appears in @var{replacement}, then it must be | |
1049 | part of one of the following sequences: | |
1050 | ||
1051 | @table @asis | |
1052 | @item @samp{\&} | |
1053 | @cindex @samp{&} in replacement | |
1054 | @samp{\&} stands for the entire text being replaced. | |
1055 | ||
1056 | @item @samp{\@var{n}} | |
1057 | @cindex @samp{\@var{n}} in replacement | |
1058 | @samp{\@var{n}}, where @var{n} is a digit, stands for the text that | |
1059 | matched the @var{n}th subexpression in the original regexp. | |
1060 | Subexpressions are those expressions grouped inside @samp{\(@dots{}\)}. | |
1061 | ||
1062 | @item @samp{\\} | |
1063 | @cindex @samp{\} in replacement | |
1064 | @samp{\\} stands for a single @samp{\} in the replacement text. | |
1065 | @end table | |
1066 | ||
1067 | If @var{subexp} is non-@code{nil}, that says to replace just | |
1068 | subexpression number @var{subexp} of the regexp that was matched, not | |
1069 | the entire match. For example, after matching @samp{foo \(ba*r\)}, | |
1070 | calling @code{replace-match} with 1 as @var{subexp} means to replace | |
1071 | just the text that matched @samp{\(ba*r\)}. | |
1072 | @end defun | |
1073 | ||
7015aca4 RS |
1074 | @node Simple Match Data |
1075 | @subsection Simple Match Data Access | |
1076 | ||
22697dac KH |
1077 | This section explains how to use the match data to find out what was |
1078 | matched by the last search or match operation. | |
1079 | ||
1080 | You can ask about the entire matching text, or about a particular | |
1081 | parenthetical subexpression of a regular expression. The @var{count} | |
1082 | argument in the functions below specifies which. If @var{count} is | |
1083 | zero, you are asking about the entire match. If @var{count} is | |
1084 | positive, it specifies which subexpression you want. | |
1085 | ||
1086 | Recall that the subexpressions of a regular expression are those | |
1087 | expressions grouped with escaped parentheses, @samp{\(@dots{}\)}. The | |
1088 | @var{count}th subexpression is found by counting occurrences of | |
1089 | @samp{\(} from the beginning of the whole regular expression. The first | |
1090 | subexpression is numbered 1, the second 2, and so on. Only regular | |
1091 | expressions can have subexpressions---after a simple string search, the | |
1092 | only information available is about the entire match. | |
1093 | ||
a9f0a989 RS |
1094 | A search which fails may or may not alter the match data. In the |
1095 | past, a failing search did not do this, but we may change it in the | |
1096 | future. | |
1097 | ||
22697dac KH |
1098 | @defun match-string count &optional in-string |
1099 | This function returns, as a string, the text matched in the last search | |
1100 | or match operation. It returns the entire text if @var{count} is zero, | |
1101 | or just the portion corresponding to the @var{count}th parenthetical | |
1102 | subexpression, if @var{count} is positive. If @var{count} is out of | |
bfe721d1 KH |
1103 | range, or if that subexpression didn't match anything, the value is |
1104 | @code{nil}. | |
22697dac KH |
1105 | |
1106 | If the last such operation was done against a string with | |
1107 | @code{string-match}, then you should pass the same string as the | |
969fe9b5 | 1108 | argument @var{in-string}. After a buffer search or match, |
22697dac KH |
1109 | you should omit @var{in-string} or pass @code{nil} for it; but you |
1110 | should make sure that the current buffer when you call | |
1111 | @code{match-string} is the one in which you did the searching or | |
1112 | matching. | |
1113 | @end defun | |
7015aca4 | 1114 | |
f9f59935 RS |
1115 | @defun match-string-no-properties count |
1116 | This function is like @code{match-string} except that the result | |
1117 | has no text properties. | |
1118 | @end defun | |
1119 | ||
7015aca4 RS |
1120 | @defun match-beginning count |
1121 | This function returns the position of the start of text matched by the | |
1122 | last regular expression searched for, or a subexpression of it. | |
1123 | ||
7fd1911a | 1124 | If @var{count} is zero, then the value is the position of the start of |
eaac2be1 | 1125 | the entire match. Otherwise, @var{count} specifies a subexpression in |
969fe9b5 | 1126 | the regular expression, and the value of the function is the starting |
22697dac KH |
1127 | position of the match for that subexpression. |
1128 | ||
1129 | The value is @code{nil} for a subexpression inside a @samp{\|} | |
1130 | alternative that wasn't used in the match. | |
7015aca4 RS |
1131 | @end defun |
1132 | ||
1133 | @defun match-end count | |
22697dac KH |
1134 | This function is like @code{match-beginning} except that it returns the |
1135 | position of the end of the match, rather than the position of the | |
1136 | beginning. | |
7015aca4 RS |
1137 | @end defun |
1138 | ||
1139 | Here is an example of using the match data, with a comment showing the | |
1140 | positions within the text: | |
1141 | ||
1142 | @example | |
1143 | @group | |
1144 | (string-match "\\(qu\\)\\(ick\\)" | |
1145 | "The quick fox jumped quickly.") | |
1146 | ;0123456789 | |
1147 | @result{} 4 | |
1148 | @end group | |
1149 | ||
22697dac KH |
1150 | @group |
1151 | (match-string 0 "The quick fox jumped quickly.") | |
1152 | @result{} "quick" | |
1153 | (match-string 1 "The quick fox jumped quickly.") | |
1154 | @result{} "qu" | |
1155 | (match-string 2 "The quick fox jumped quickly.") | |
1156 | @result{} "ick" | |
1157 | @end group | |
1158 | ||
7015aca4 RS |
1159 | @group |
1160 | (match-beginning 1) ; @r{The beginning of the match} | |
1161 | @result{} 4 ; @r{with @samp{qu} is at index 4.} | |
1162 | @end group | |
1163 | ||
1164 | @group | |
1165 | (match-beginning 2) ; @r{The beginning of the match} | |
1166 | @result{} 6 ; @r{with @samp{ick} is at index 6.} | |
1167 | @end group | |
1168 | ||
1169 | @group | |
1170 | (match-end 1) ; @r{The end of the match} | |
1171 | @result{} 6 ; @r{with @samp{qu} is at index 6.} | |
1172 | ||
1173 | (match-end 2) ; @r{The end of the match} | |
1174 | @result{} 9 ; @r{with @samp{ick} is at index 9.} | |
1175 | @end group | |
1176 | @end example | |
1177 | ||
1178 | Here is another example. Point is initially located at the beginning | |
1179 | of the line. Searching moves point to between the space and the word | |
1180 | @samp{in}. The beginning of the entire match is at the 9th character of | |
1181 | the buffer (@samp{T}), and the beginning of the match for the first | |
1182 | subexpression is at the 13th character (@samp{c}). | |
1183 | ||
1184 | @example | |
1185 | @group | |
1186 | (list | |
1187 | (re-search-forward "The \\(cat \\)") | |
1188 | (match-beginning 0) | |
1189 | (match-beginning 1)) | |
7fd1911a | 1190 | @result{} (9 9 13) |
7015aca4 RS |
1191 | @end group |
1192 | ||
1193 | @group | |
1194 | ---------- Buffer: foo ---------- | |
1195 | I read "The cat @point{}in the hat comes back" twice. | |
1196 | ^ ^ | |
1197 | 9 13 | |
1198 | ---------- Buffer: foo ---------- | |
1199 | @end group | |
1200 | @end example | |
1201 | ||
1202 | @noindent | |
1203 | (In this case, the index returned is a buffer position; the first | |
1204 | character of the buffer counts as 1.) | |
1205 | ||
7015aca4 RS |
1206 | @node Entire Match Data |
1207 | @subsection Accessing the Entire Match Data | |
1208 | ||
1209 | The functions @code{match-data} and @code{set-match-data} read or | |
1210 | write the entire match data, all at once. | |
1211 | ||
1212 | @defun match-data | |
1213 | This function returns a newly constructed list containing all the | |
1214 | information on what text the last search matched. Element zero is the | |
1215 | position of the beginning of the match for the whole expression; element | |
1216 | one is the position of the end of the match for the expression. The | |
1217 | next two elements are the positions of the beginning and end of the | |
1218 | match for the first subexpression, and so on. In general, element | |
1219 | @ifinfo | |
1220 | number 2@var{n} | |
1221 | @end ifinfo | |
1222 | @tex | |
1223 | number {\mathsurround=0pt $2n$} | |
1224 | @end tex | |
1225 | corresponds to @code{(match-beginning @var{n})}; and | |
1226 | element | |
1227 | @ifinfo | |
1228 | number 2@var{n} + 1 | |
1229 | @end ifinfo | |
1230 | @tex | |
1231 | number {\mathsurround=0pt $2n+1$} | |
1232 | @end tex | |
1233 | corresponds to @code{(match-end @var{n})}. | |
1234 | ||
1235 | All the elements are markers or @code{nil} if matching was done on a | |
1236 | buffer, and all are integers or @code{nil} if matching was done on a | |
969fe9b5 | 1237 | string with @code{string-match}. |
7015aca4 RS |
1238 | |
1239 | As always, there must be no possibility of intervening searches between | |
1240 | the call to a search function and the call to @code{match-data} that is | |
1241 | intended to access the match data for that search. | |
1242 | ||
1243 | @example | |
1244 | @group | |
1245 | (match-data) | |
1246 | @result{} (#<marker at 9 in foo> | |
1247 | #<marker at 17 in foo> | |
1248 | #<marker at 13 in foo> | |
1249 | #<marker at 17 in foo>) | |
1250 | @end group | |
1251 | @end example | |
1252 | @end defun | |
1253 | ||
1254 | @defun set-match-data match-list | |
1255 | This function sets the match data from the elements of @var{match-list}, | |
1256 | which should be a list that was the value of a previous call to | |
1257 | @code{match-data}. | |
1258 | ||
1259 | If @var{match-list} refers to a buffer that doesn't exist, you don't get | |
1260 | an error; that sets the match data in a meaningless but harmless way. | |
1261 | ||
1262 | @findex store-match-data | |
969fe9b5 | 1263 | @code{store-match-data} is a semi-obsolete alias for @code{set-match-data}. |
7015aca4 RS |
1264 | @end defun |
1265 | ||
1266 | @node Saving Match Data | |
1267 | @subsection Saving and Restoring the Match Data | |
1268 | ||
d1280259 RS |
1269 | When you call a function that may do a search, you may need to save |
1270 | and restore the match data around that call, if you want to preserve the | |
1271 | match data from an earlier search for later use. Here is an example | |
1272 | that shows the problem that arises if you fail to save the match data: | |
7015aca4 RS |
1273 | |
1274 | @example | |
1275 | @group | |
1276 | (re-search-forward "The \\(cat \\)") | |
1277 | @result{} 48 | |
1278 | (foo) ; @r{Perhaps @code{foo} does} | |
1279 | ; @r{more searching.} | |
1280 | (match-end 0) | |
1281 | @result{} 61 ; @r{Unexpected result---not 48!} | |
1282 | @end group | |
1283 | @end example | |
1284 | ||
d1280259 | 1285 | You can save and restore the match data with @code{save-match-data}: |
7015aca4 | 1286 | |
bfe721d1 | 1287 | @defmac save-match-data body@dots{} |
1911e6e5 | 1288 | This macro executes @var{body}, saving and restoring the match |
d1280259 | 1289 | data around it. |
bfe721d1 | 1290 | @end defmac |
7015aca4 | 1291 | |
969fe9b5 RS |
1292 | You could use @code{set-match-data} together with @code{match-data} to |
1293 | imitate the effect of the special form @code{save-match-data}. Here is | |
1294 | how: | |
7015aca4 RS |
1295 | |
1296 | @example | |
1297 | @group | |
1298 | (let ((data (match-data))) | |
1299 | (unwind-protect | |
f9f59935 | 1300 | @dots{} ; @r{Ok to change the original match data.} |
7015aca4 RS |
1301 | (set-match-data data))) |
1302 | @end group | |
1303 | @end example | |
1304 | ||
d1280259 RS |
1305 | Emacs automatically saves and restores the match data when it runs |
1306 | process filter functions (@pxref{Filter Functions}) and process | |
1307 | sentinels (@pxref{Sentinels}). | |
1308 | ||
7015aca4 RS |
1309 | @ignore |
1310 | Here is a function which restores the match data provided the buffer | |
1311 | associated with it still exists. | |
1312 | ||
1313 | @smallexample | |
1314 | @group | |
1315 | (defun restore-match-data (data) | |
1316 | @c It is incorrect to split the first line of a doc string. | |
1317 | @c If there's a problem here, it should be solved in some other way. | |
1318 | "Restore the match data DATA unless the buffer is missing." | |
1319 | (catch 'foo | |
1320 | (let ((d data)) | |
1321 | @end group | |
1322 | (while d | |
1323 | (and (car d) | |
1324 | (null (marker-buffer (car d))) | |
1325 | @group | |
1326 | ;; @file{match-data} @r{buffer is deleted.} | |
1327 | (throw 'foo nil)) | |
1328 | (setq d (cdr d))) | |
1329 | (set-match-data data)))) | |
1330 | @end group | |
1331 | @end smallexample | |
1332 | @end ignore | |
1333 | ||
1334 | @node Searching and Case | |
1335 | @section Searching and Case | |
1336 | @cindex searching and case | |
1337 | ||
1338 | By default, searches in Emacs ignore the case of the text they are | |
1339 | searching through; if you specify searching for @samp{FOO}, then | |
f9f59935 RS |
1340 | @samp{Foo} or @samp{foo} is also considered a match. This applies to |
1341 | regular expressions, too; thus, @samp{[aB]} would match @samp{a} or | |
1342 | @samp{A} or @samp{b} or @samp{B}. | |
7015aca4 RS |
1343 | |
1344 | If you do not want this feature, set the variable | |
1345 | @code{case-fold-search} to @code{nil}. Then all letters must match | |
7fd1911a RS |
1346 | exactly, including case. This is a buffer-local variable; altering the |
1347 | variable affects only the current buffer. (@xref{Intro to | |
7015aca4 RS |
1348 | Buffer-Local}.) Alternatively, you may change the value of |
1349 | @code{default-case-fold-search}, which is the default value of | |
1350 | @code{case-fold-search} for buffers that do not override it. | |
1351 | ||
1352 | Note that the user-level incremental search feature handles case | |
1353 | distinctions differently. When given a lower case letter, it looks for | |
1354 | a match of either case, but when given an upper case letter, it looks | |
1355 | for an upper case letter only. But this has nothing to do with the | |
f9f59935 | 1356 | searching functions used in Lisp code. |
7015aca4 RS |
1357 | |
1358 | @defopt case-replace | |
7fd1911a RS |
1359 | This variable determines whether the replacement functions should |
1360 | preserve case. If the variable is @code{nil}, that means to use the | |
1361 | replacement text verbatim. A non-@code{nil} value means to convert the | |
1362 | case of the replacement text according to the text being replaced. | |
1363 | ||
1364 | The function @code{replace-match} is where this variable actually has | |
1365 | its effect. @xref{Replacing Match}. | |
7015aca4 RS |
1366 | @end defopt |
1367 | ||
1368 | @defopt case-fold-search | |
1369 | This buffer-local variable determines whether searches should ignore | |
1370 | case. If the variable is @code{nil} they do not ignore case; otherwise | |
1371 | they do ignore case. | |
1372 | @end defopt | |
1373 | ||
1374 | @defvar default-case-fold-search | |
1375 | The value of this variable is the default value for | |
1376 | @code{case-fold-search} in buffers that do not override it. This is the | |
1377 | same as @code{(default-value 'case-fold-search)}. | |
1378 | @end defvar | |
1379 | ||
1380 | @node Standard Regexps | |
1381 | @section Standard Regular Expressions Used in Editing | |
1382 | @cindex regexps used standardly in editing | |
1383 | @cindex standard regexps used in editing | |
1384 | ||
1385 | This section describes some variables that hold regular expressions | |
1386 | used for certain purposes in editing: | |
1387 | ||
1388 | @defvar page-delimiter | |
969fe9b5 RS |
1389 | This is the regular expression describing line-beginnings that separate |
1390 | pages. The default value is @code{"^\014"} (i.e., @code{"^^L"} or | |
1391 | @code{"^\C-l"}); this matches a line that starts with a formfeed | |
1392 | character. | |
7015aca4 RS |
1393 | @end defvar |
1394 | ||
22697dac KH |
1395 | The following two regular expressions should @emph{not} assume the |
1396 | match always starts at the beginning of a line; they should not use | |
1397 | @samp{^} to anchor the match. Most often, the paragraph commands do | |
1398 | check for a match only at the beginning of a line, which means that | |
bfe721d1 KH |
1399 | @samp{^} would be superfluous. When there is a nonzero left margin, |
1400 | they accept matches that start after the left margin. In that case, a | |
1401 | @samp{^} would be incorrect. However, a @samp{^} is harmless in modes | |
1402 | where a left margin is never used. | |
22697dac | 1403 | |
7015aca4 RS |
1404 | @defvar paragraph-separate |
1405 | This is the regular expression for recognizing the beginning of a line | |
1406 | that separates paragraphs. (If you change this, you may have to | |
7fd1911a | 1407 | change @code{paragraph-start} also.) The default value is |
22697dac KH |
1408 | @w{@code{"[@ \t\f]*$"}}, which matches a line that consists entirely of |
1409 | spaces, tabs, and form feeds (after its left margin). | |
7015aca4 RS |
1410 | @end defvar |
1411 | ||
1412 | @defvar paragraph-start | |
1413 | This is the regular expression for recognizing the beginning of a line | |
1414 | that starts @emph{or} separates paragraphs. The default value is | |
22697dac KH |
1415 | @w{@code{"[@ \t\n\f]"}}, which matches a line starting with a space, tab, |
1416 | newline, or form feed (after its left margin). | |
7015aca4 RS |
1417 | @end defvar |
1418 | ||
1419 | @defvar sentence-end | |
1420 | This is the regular expression describing the end of a sentence. (All | |
1421 | paragraph boundaries also end sentences, regardless.) The default value | |
1422 | is: | |
1423 | ||
1424 | @example | |
7fd1911a | 1425 | "[.?!][]\"')@}]*\\($\\| $\\|\t\\| \\)[ \t\n]*" |
7015aca4 RS |
1426 | @end example |
1427 | ||
7fd1911a RS |
1428 | This means a period, question mark or exclamation mark, followed |
1429 | optionally by a closing parenthetical character, followed by tabs, | |
1430 | spaces or new lines. | |
7015aca4 RS |
1431 | |
1432 | For a detailed explanation of this regular expression, see @ref{Regexp | |
1433 | Example}. | |
1434 | @end defvar |