Commit | Line | Data |
---|---|---|
7015aca4 RS |
1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
651f374c | 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2002, 2003, |
ceb4c4d3 | 4 | @c 2004, 2005, 2006 Free Software Foundation, Inc. |
7015aca4 RS |
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. | |
99543e8b | 19 | * Searching and Case:: Case-independent or case-significant searching. |
7015aca4 RS |
20 | * Regular Expressions:: Describing classes of strings. |
21 | * Regexp Search:: Searching for a match for a regexp. | |
22697dac | 22 | * POSIX Regexps:: Searching POSIX-style for the longest match. |
2a233172 RS |
23 | * Match Data:: Finding out which part of the text matched, |
24 | after a string or regexp search. | |
99543e8b | 25 | * Search and Replace:: Commands that loop, searching and replacing. |
7015aca4 RS |
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 |
7015aca4 RS |
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 |
7015aca4 RS |
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 |
7015aca4 RS |
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 | |
f9f59935 RS |
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 | |
61cfa852 RS |
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. | |
7015aca4 RS |
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 | ||
5bb8ca2a RS |
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. | |
7015aca4 RS |
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}. |
7015aca4 RS |
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 | ||
99543e8b RS |
160 | @node Searching and Case |
161 | @section Searching and Case | |
162 | @cindex searching and case | |
163 | ||
164 | By default, searches in Emacs ignore the case of the text they are | |
165 | searching through; if you specify searching for @samp{FOO}, then | |
166 | @samp{Foo} or @samp{foo} is also considered a match. This applies to | |
167 | regular expressions, too; thus, @samp{[aB]} would match @samp{a} or | |
168 | @samp{A} or @samp{b} or @samp{B}. | |
169 | ||
170 | If you do not want this feature, set the variable | |
171 | @code{case-fold-search} to @code{nil}. Then all letters must match | |
172 | exactly, including case. This is a buffer-local variable; altering the | |
173 | variable affects only the current buffer. (@xref{Intro to | |
174 | Buffer-Local}.) Alternatively, you may change the value of | |
175 | @code{default-case-fold-search}, which is the default value of | |
176 | @code{case-fold-search} for buffers that do not override it. | |
177 | ||
178 | Note that the user-level incremental search feature handles case | |
179 | distinctions differently. When given a lower case letter, it looks for | |
180 | a match of either case, but when given an upper case letter, it looks | |
181 | for an upper case letter only. But this has nothing to do with the | |
182 | searching functions used in Lisp code. | |
183 | ||
184 | @defopt case-replace | |
185 | This variable determines whether the higher level replacement | |
186 | functions should preserve case. If the variable is @code{nil}, that | |
187 | means to use the replacement text verbatim. A non-@code{nil} value | |
188 | means to convert the case of the replacement text according to the | |
189 | text being replaced. | |
190 | ||
191 | This variable is used by passing it as an argument to the function | |
192 | @code{replace-match}. @xref{Replacing Match}. | |
193 | @end defopt | |
194 | ||
195 | @defopt case-fold-search | |
196 | This buffer-local variable determines whether searches should ignore | |
197 | case. If the variable is @code{nil} they do not ignore case; otherwise | |
198 | they do ignore case. | |
199 | @end defopt | |
200 | ||
201 | @defvar default-case-fold-search | |
202 | The value of this variable is the default value for | |
203 | @code{case-fold-search} in buffers that do not override it. This is the | |
204 | same as @code{(default-value 'case-fold-search)}. | |
205 | @end defvar | |
206 | ||
7015aca4 RS |
207 | @node Regular Expressions |
208 | @section Regular Expressions | |
209 | @cindex regular expression | |
210 | @cindex regexp | |
211 | ||
212 | A @dfn{regular expression} (@dfn{regexp}, for short) is a pattern that | |
213 | denotes a (possibly infinite) set of strings. Searching for matches for | |
214 | a regexp is a very powerful operation. This section explains how to write | |
215 | regexps; the following section says how to search for them. | |
216 | ||
85b6b13c RS |
217 | @findex re-builder |
218 | @cindex authoring regular expressions | |
219 | For convenient interactive development of regular expressions, you | |
220 | can use the @kbd{M-x re-builder} command. It provides a convenient | |
221 | interface for creating regular expressions, by giving immediate visual | |
222 | feedback in a separate buffer. As you edit the regexp, all its | |
223 | matches in the target buffer are highlighted. Each parenthesized | |
224 | sub-expression of the regexp is shown in a distinct face, which makes | |
225 | it easier to verify even very complex regexps. | |
226 | ||
7015aca4 RS |
227 | @menu |
228 | * Syntax of Regexps:: Rules for writing regular expressions. | |
229 | * Regexp Example:: Illustrates regular expression syntax. | |
bcb6b6b8 | 230 | * Regexp Functions:: Functions for operating on regular expressions. |
7015aca4 RS |
231 | @end menu |
232 | ||
233 | @node Syntax of Regexps | |
234 | @subsection Syntax of Regular Expressions | |
235 | ||
61cfa852 RS |
236 | Regular expressions have a syntax in which a few characters are |
237 | special constructs and the rest are @dfn{ordinary}. An ordinary | |
238 | character is a simple regular expression that matches that character and | |
239 | nothing else. The special characters are @samp{.}, @samp{*}, @samp{+}, | |
240 | @samp{?}, @samp{[}, @samp{]}, @samp{^}, @samp{$}, and @samp{\}; no new | |
241 | special characters will be defined in the future. Any other character | |
242 | appearing in a regular expression is ordinary, unless a @samp{\} | |
243 | precedes it. | |
7015aca4 | 244 | |
8241495d | 245 | For example, @samp{f} is not a special character, so it is ordinary, and |
7015aca4 RS |
246 | therefore @samp{f} is a regular expression that matches the string |
247 | @samp{f} and no other string. (It does @emph{not} match the string | |
8241495d RS |
248 | @samp{fg}, but it does match a @emph{part} of that string.) Likewise, |
249 | @samp{o} is a regular expression that matches only @samp{o}.@refill | |
7015aca4 | 250 | |
8241495d | 251 | Any two regular expressions @var{a} and @var{b} can be concatenated. The |
61cfa852 | 252 | result is a regular expression that matches a string if @var{a} matches |
7015aca4 RS |
253 | some amount of the beginning of that string and @var{b} matches the rest of |
254 | the string.@refill | |
255 | ||
8241495d | 256 | As a simple example, we can concatenate the regular expressions @samp{f} |
7015aca4 RS |
257 | and @samp{o} to get the regular expression @samp{fo}, which matches only |
258 | the string @samp{fo}. Still trivial. To do something more powerful, you | |
8241495d RS |
259 | need to use one of the special regular expression constructs. |
260 | ||
261 | @menu | |
262 | * Regexp Special:: Special characters in regular expressions. | |
263 | * Char Classes:: Character classes used in regular expressions. | |
264 | * Regexp Backslash:: Backslash-sequences in regular expressions. | |
265 | @end menu | |
266 | ||
267 | @node Regexp Special | |
268 | @subsubsection Special Characters in Regular Expressions | |
269 | ||
270 | Here is a list of the characters that are special in a regular | |
271 | expression. | |
7015aca4 | 272 | |
7dd3d99f | 273 | @need 800 |
969fe9b5 RS |
274 | @table @asis |
275 | @item @samp{.}@: @r{(Period)} | |
7015aca4 RS |
276 | @cindex @samp{.} in regexp |
277 | is a special character that matches any single character except a newline. | |
278 | Using concatenation, we can make regular expressions like @samp{a.b}, which | |
279 | matches any three-character string that begins with @samp{a} and ends with | |
280 | @samp{b}.@refill | |
281 | ||
969fe9b5 | 282 | @item @samp{*} |
7015aca4 | 283 | @cindex @samp{*} in regexp |
1cd71ce0 RS |
284 | is not a construct by itself; it is a postfix operator that means to |
285 | match the preceding regular expression repetitively as many times as | |
286 | possible. Thus, @samp{o*} matches any number of @samp{o}s (including no | |
287 | @samp{o}s). | |
7015aca4 RS |
288 | |
289 | @samp{*} always applies to the @emph{smallest} possible preceding | |
1cd71ce0 RS |
290 | expression. Thus, @samp{fo*} has a repeating @samp{o}, not a repeating |
291 | @samp{fo}. It matches @samp{f}, @samp{fo}, @samp{foo}, and so on. | |
7015aca4 | 292 | |
f9f59935 RS |
293 | The matcher processes a @samp{*} construct by matching, immediately, as |
294 | many repetitions as can be found. Then it continues with the rest of | |
295 | the pattern. If that fails, backtracking occurs, discarding some of the | |
296 | matches of the @samp{*}-modified construct in the hope that that will | |
297 | make it possible to match the rest of the pattern. For example, in | |
298 | matching @samp{ca*ar} against the string @samp{caaar}, the @samp{a*} | |
299 | first tries to match all three @samp{a}s; but the rest of the pattern is | |
7015aca4 | 300 | @samp{ar} and there is only @samp{r} left to match, so this try fails. |
f9f59935 RS |
301 | The next alternative is for @samp{a*} to match only two @samp{a}s. With |
302 | this choice, the rest of the regexp matches successfully.@refill | |
7015aca4 | 303 | |
342fd6cd RS |
304 | Nested repetition operators take a long time, or even forever, if they |
305 | lead to ambiguous matching. For example, trying to match the regular | |
306 | expression @samp{\(x+y*\)*a} against the string | |
307 | @samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz} could take hours before it | |
308 | ultimately fails. Emacs must try each way of grouping the 35 | |
309 | @samp{x}s before concluding that none of them can work. Even worse, | |
310 | @samp{\(x*\)*} can match the null string in infinitely many ways, so | |
311 | it causes an infinite loop. To avoid these problems, check nested | |
312 | repetitions carefully. | |
73031603 | 313 | |
969fe9b5 | 314 | @item @samp{+} |
7015aca4 | 315 | @cindex @samp{+} in regexp |
1cd71ce0 RS |
316 | is a postfix operator, similar to @samp{*} except that it must match |
317 | the preceding expression at least once. So, for example, @samp{ca+r} | |
7015aca4 RS |
318 | matches the strings @samp{car} and @samp{caaaar} but not the string |
319 | @samp{cr}, whereas @samp{ca*r} matches all three strings. | |
320 | ||
969fe9b5 | 321 | @item @samp{?} |
7015aca4 | 322 | @cindex @samp{?} in regexp |
f9f59935 | 323 | is a postfix operator, similar to @samp{*} except that it must match the |
1cd71ce0 RS |
324 | preceding expression either once or not at all. For example, |
325 | @samp{ca?r} matches @samp{car} or @samp{cr}; nothing else. | |
7015aca4 | 326 | |
c082a348 RS |
327 | @item @samp{*?}, @samp{+?}, @samp{??} |
328 | These are ``non-greedy'' variants of the operators @samp{*}, @samp{+} | |
329 | and @samp{?}. Where those operators match the largest possible | |
330 | substring (consistent with matching the entire containing expression), | |
331 | the non-greedy variants match the smallest possible substring | |
332 | (consistent with matching the entire containing expression). | |
333 | ||
334 | For example, the regular expression @samp{c[ad]*a} when applied to the | |
335 | string @samp{cdaaada} matches the whole string; but the regular | |
336 | expression @samp{c[ad]*?a}, applied to that same string, matches just | |
337 | @samp{cda}. (The smallest possible match here for @samp{[ad]*?} that | |
338 | permits the whole expression to match is @samp{d}.) | |
339 | ||
969fe9b5 RS |
340 | @item @samp{[ @dots{} ]} |
341 | @cindex character alternative (in regexp) | |
7015aca4 RS |
342 | @cindex @samp{[} in regexp |
343 | @cindex @samp{]} in regexp | |
969fe9b5 RS |
344 | is a @dfn{character alternative}, which begins with @samp{[} and is |
345 | terminated by @samp{]}. In the simplest case, the characters between | |
346 | the two brackets are what this character alternative can match. | |
1cd71ce0 RS |
347 | |
348 | Thus, @samp{[ad]} matches either one @samp{a} or one @samp{d}, and | |
349 | @samp{[ad]*} matches any string composed of just @samp{a}s and @samp{d}s | |
350 | (including the empty string), from which it follows that @samp{c[ad]*r} | |
351 | matches @samp{cr}, @samp{car}, @samp{cdr}, @samp{caddaar}, etc. | |
352 | ||
969fe9b5 RS |
353 | You can also include character ranges in a character alternative, by |
354 | writing the starting and ending characters with a @samp{-} between them. | |
bcb6b6b8 LT |
355 | Thus, @samp{[a-z]} matches any lower-case @acronym{ASCII} letter. |
356 | Ranges may be intermixed freely with individual characters, as in | |
357 | @samp{[a-z$%.]}, which matches any lower case @acronym{ASCII} letter | |
358 | or @samp{$}, @samp{%} or period. | |
1cd71ce0 RS |
359 | |
360 | Note that the usual regexp special characters are not special inside a | |
86494bd5 | 361 | character alternative. A completely different set of characters is |
969fe9b5 | 362 | special inside character alternatives: @samp{]}, @samp{-} and @samp{^}. |
1cd71ce0 | 363 | |
969fe9b5 RS |
364 | To include a @samp{]} in a character alternative, you must make it the |
365 | first character. For example, @samp{[]a]} matches @samp{]} or @samp{a}. | |
366 | To include a @samp{-}, write @samp{-} as the first or last character of | |
367 | the character alternative, or put it after a range. Thus, @samp{[]-]} | |
368 | matches both @samp{]} and @samp{-}. | |
7015aca4 | 369 | |
969fe9b5 RS |
370 | To include @samp{^} in a character alternative, put it anywhere but at |
371 | the beginning. | |
7015aca4 | 372 | |
8f17d892 RS |
373 | The beginning and end of a range of multibyte characters must be in |
374 | the same character set (@pxref{Character Sets}). Thus, | |
375 | @code{"[\x8e0-\x97c]"} is invalid because character 0x8e0 (@samp{a} | |
376 | with grave accent) is in the Emacs character set for Latin-1 but the | |
377 | character 0x97c (@samp{u} with diaeresis) is in the Emacs character | |
378 | set for Latin-2. (We use Lisp string syntax to write that example, | |
379 | and a few others in the next few paragraphs, in order to include hex | |
380 | escape sequences in them.) | |
6cc089d2 DL |
381 | |
382 | If a range starts with a unibyte character @var{c} and ends with a | |
383 | multibyte character @var{c2}, the range is divided into two parts: one | |
384 | is @samp{@var{c}..?\377}, the other is @samp{@var{c1}..@var{c2}}, where | |
385 | @var{c1} is the first character of the charset to which @var{c2} | |
386 | belongs. | |
177c0ea7 | 387 | |
ad800164 | 388 | You cannot always match all non-@acronym{ASCII} characters with the regular |
8f17d892 | 389 | expression @code{"[\200-\377]"}. This works when searching a unibyte |
8241495d | 390 | buffer or string (@pxref{Text Representations}), but not in a multibyte |
ad800164 | 391 | buffer or string, because many non-@acronym{ASCII} characters have codes |
8f17d892 | 392 | above octal 0377. However, the regular expression @code{"[^\000-\177]"} |
ad800164 | 393 | does match all non-@acronym{ASCII} characters (see below regarding @samp{^}), |
8241495d | 394 | in both multibyte and unibyte representations, because only the |
ad800164 | 395 | @acronym{ASCII} characters are excluded. |
8241495d | 396 | |
63f508b4 | 397 | A character alternative can also specify named |
8241495d RS |
398 | character classes (@pxref{Char Classes}). This is a POSIX feature whose |
399 | syntax is @samp{[:@var{class}:]}. Using a character class is equivalent | |
400 | to mentioning each of the characters in that class; but the latter is | |
401 | not feasible in practice, since some classes include thousands of | |
402 | different characters. | |
403 | ||
969fe9b5 | 404 | @item @samp{[^ @dots{} ]} |
7015aca4 | 405 | @cindex @samp{^} in regexp |
342fd6cd RS |
406 | @samp{[^} begins a @dfn{complemented character alternative}. This |
407 | matches any character except the ones specified. Thus, | |
408 | @samp{[^a-z0-9A-Z]} matches all characters @emph{except} letters and | |
409 | digits. | |
7015aca4 | 410 | |
969fe9b5 | 411 | @samp{^} is not special in a character alternative unless it is the first |
7015aca4 | 412 | character. The character following the @samp{^} is treated as if it |
1cd71ce0 | 413 | were first (in other words, @samp{-} and @samp{]} are not special there). |
7015aca4 | 414 | |
969fe9b5 | 415 | A complemented character alternative can match a newline, unless newline is |
1cd71ce0 RS |
416 | mentioned as one of the characters not to match. This is in contrast to |
417 | the handling of regexps in programs such as @code{grep}. | |
7015aca4 | 418 | |
969fe9b5 | 419 | @item @samp{^} |
7015aca4 | 420 | @cindex beginning of line in regexp |
bcb6b6b8 LT |
421 | When matching a buffer, @samp{^} matches the empty string, but only at the |
422 | beginning of a line in the text being matched (or the beginning of the | |
423 | accessible portion of the buffer). Otherwise it fails to match | |
424 | anything. Thus, @samp{^foo} matches a @samp{foo} that occurs at the | |
425 | beginning of a line. | |
7015aca4 | 426 | |
61cfa852 | 427 | When matching a string instead of a buffer, @samp{^} matches at the |
8f17d892 | 428 | beginning of the string or after a newline character. |
7015aca4 | 429 | |
8241495d RS |
430 | For historical compatibility reasons, @samp{^} can be used only at the |
431 | beginning of the regular expression, or after @samp{\(} or @samp{\|}. | |
432 | ||
969fe9b5 | 433 | @item @samp{$} |
7015aca4 | 434 | @cindex @samp{$} in regexp |
8241495d | 435 | @cindex end of line in regexp |
bcb6b6b8 LT |
436 | is similar to @samp{^} but matches only at the end of a line (or the |
437 | end of the accessible portion of the buffer). Thus, @samp{x+$} | |
438 | matches a string of one @samp{x} or more at the end of a line. | |
7015aca4 | 439 | |
61cfa852 | 440 | When matching a string instead of a buffer, @samp{$} matches at the end |
8f17d892 | 441 | of the string or before a newline character. |
7015aca4 | 442 | |
8241495d RS |
443 | For historical compatibility reasons, @samp{$} can be used only at the |
444 | end of the regular expression, or before @samp{\)} or @samp{\|}. | |
445 | ||
969fe9b5 | 446 | @item @samp{\} |
7015aca4 RS |
447 | @cindex @samp{\} in regexp |
448 | has two functions: it quotes the special characters (including | |
449 | @samp{\}), and it introduces additional special constructs. | |
450 | ||
451 | Because @samp{\} quotes special characters, @samp{\$} is a regular | |
61cfa852 RS |
452 | expression that matches only @samp{$}, and @samp{\[} is a regular |
453 | expression that matches only @samp{[}, and so on. | |
7015aca4 RS |
454 | |
455 | Note that @samp{\} also has special meaning in the read syntax of Lisp | |
456 | strings (@pxref{String Type}), and must be quoted with @samp{\}. For | |
457 | example, the regular expression that matches the @samp{\} character is | |
458 | @samp{\\}. To write a Lisp string that contains the characters | |
459 | @samp{\\}, Lisp syntax requires you to quote each @samp{\} with another | |
460 | @samp{\}. Therefore, the read syntax for a regular expression matching | |
461 | @samp{\} is @code{"\\\\"}.@refill | |
462 | @end table | |
463 | ||
b22f3a19 | 464 | @strong{Please note:} For historical compatibility, special characters |
7015aca4 RS |
465 | are treated as ordinary ones if they are in contexts where their special |
466 | meanings make no sense. For example, @samp{*foo} treats @samp{*} as | |
467 | ordinary since there is no preceding expression on which the @samp{*} | |
61cfa852 RS |
468 | can act. It is poor practice to depend on this behavior; quote the |
469 | special character anyway, regardless of where it appears.@refill | |
7015aca4 | 470 | |
8241495d RS |
471 | @node Char Classes |
472 | @subsubsection Character Classes | |
473 | @cindex character classes in regexp | |
474 | ||
475 | Here is a table of the classes you can use in a character alternative, | |
63f508b4 | 476 | and what they mean: |
8241495d RS |
477 | |
478 | @table @samp | |
479 | @item [:ascii:] | |
ad800164 | 480 | This matches any @acronym{ASCII} (unibyte) character. |
8241495d RS |
481 | @item [:alnum:] |
482 | This matches any letter or digit. (At present, for multibyte | |
483 | characters, it matches anything that has word syntax.) | |
484 | @item [:alpha:] | |
485 | This matches any letter. (At present, for multibyte characters, it | |
486 | matches anything that has word syntax.) | |
487 | @item [:blank:] | |
488 | This matches space and tab only. | |
489 | @item [:cntrl:] | |
ad800164 | 490 | This matches any @acronym{ASCII} control character. |
8241495d RS |
491 | @item [:digit:] |
492 | This matches @samp{0} through @samp{9}. Thus, @samp{[-+[:digit:]]} | |
493 | matches any digit, as well as @samp{+} and @samp{-}. | |
494 | @item [:graph:] | |
ad800164 | 495 | This matches graphic characters---everything except @acronym{ASCII} control |
75708135 | 496 | characters, space, and the delete character. |
8241495d RS |
497 | @item [:lower:] |
498 | This matches any lower-case letter, as determined by | |
499 | the current case table (@pxref{Case Tables}). | |
500 | @item [:nonascii:] | |
ad800164 | 501 | This matches any non-@acronym{ASCII} (multibyte) character. |
8241495d | 502 | @item [:print:] |
ad800164 | 503 | This matches printing characters---everything except @acronym{ASCII} control |
caccdcbb | 504 | characters and the delete character. |
8241495d RS |
505 | @item [:punct:] |
506 | This matches any punctuation character. (At present, for multibyte | |
507 | characters, it matches anything that has non-word syntax.) | |
508 | @item [:space:] | |
509 | This matches any character that has whitespace syntax | |
510 | (@pxref{Syntax Class Table}). | |
511 | @item [:upper:] | |
512 | This matches any upper-case letter, as determined by | |
513 | the current case table (@pxref{Case Tables}). | |
514 | @item [:word:] | |
515 | This matches any character that has word syntax (@pxref{Syntax Class | |
516 | Table}). | |
517 | @item [:xdigit:] | |
518 | This matches the hexadecimal digits: @samp{0} through @samp{9}, @samp{a} | |
519 | through @samp{f} and @samp{A} through @samp{F}. | |
520 | @end table | |
521 | ||
522 | @node Regexp Backslash | |
523 | @subsubsection Backslash Constructs in Regular Expressions | |
524 | ||
525 | For the most part, @samp{\} followed by any character matches only | |
526 | that character. However, there are several exceptions: certain | |
527 | two-character sequences starting with @samp{\} that have special | |
528 | meanings. (The character after the @samp{\} in such a sequence is | |
529 | always ordinary when used on its own.) Here is a table of the special | |
530 | @samp{\} constructs. | |
7015aca4 | 531 | |
969fe9b5 | 532 | @table @samp |
7015aca4 RS |
533 | @item \| |
534 | @cindex @samp{|} in regexp | |
535 | @cindex regexp alternative | |
536 | specifies an alternative. | |
537 | Two regular expressions @var{a} and @var{b} with @samp{\|} in | |
538 | between form an expression that matches anything that either @var{a} or | |
539 | @var{b} matches.@refill | |
540 | ||
541 | Thus, @samp{foo\|bar} matches either @samp{foo} or @samp{bar} | |
542 | but no other string.@refill | |
543 | ||
544 | @samp{\|} applies to the largest possible surrounding expressions. Only a | |
545 | surrounding @samp{\( @dots{} \)} grouping can limit the grouping power of | |
546 | @samp{\|}.@refill | |
547 | ||
01913af2 RS |
548 | If you need full backtracking capability to handle multiple uses of |
549 | @samp{\|}, use the POSIX regular expression functions (@pxref{POSIX | |
550 | Regexps}). | |
7015aca4 | 551 | |
2d06696f RS |
552 | @item \@{@var{m}\@} |
553 | is a postfix operator that repeats the previous pattern exactly @var{m} | |
554 | times. Thus, @samp{x\@{5\@}} matches the string @samp{xxxxx} | |
555 | and nothing else. @samp{c[ad]\@{3\@}r} matches string such as | |
556 | @samp{caaar}, @samp{cdddr}, @samp{cadar}, and so on. | |
557 | ||
558 | @item \@{@var{m},@var{n}\@} | |
2a233172 | 559 | is a more general postfix operator that specifies repetition with a |
2d06696f RS |
560 | minimum of @var{m} repeats and a maximum of @var{n} repeats. If @var{m} |
561 | is omitted, the minimum is 0; if @var{n} is omitted, there is no | |
562 | maximum. | |
563 | ||
564 | For example, @samp{c[ad]\@{1,2\@}r} matches the strings @samp{car}, | |
565 | @samp{cdr}, @samp{caar}, @samp{cadr}, @samp{cdar}, and @samp{cddr}, and | |
566 | nothing else.@* | |
567 | @samp{\@{0,1\@}} or @samp{\@{,1\@}} is equivalent to @samp{?}. @* | |
568 | @samp{\@{0,\@}} or @samp{\@{,\@}} is equivalent to @samp{*}. @* | |
569 | @samp{\@{1,\@}} is equivalent to @samp{+}. | |
570 | ||
7015aca4 RS |
571 | @item \( @dots{} \) |
572 | @cindex @samp{(} in regexp | |
573 | @cindex @samp{)} in regexp | |
574 | @cindex regexp grouping | |
575 | is a grouping construct that serves three purposes: | |
576 | ||
577 | @enumerate | |
578 | @item | |
9e2b495b RS |
579 | To enclose a set of @samp{\|} alternatives for other operations. Thus, |
580 | the regular expression @samp{\(foo\|bar\)x} matches either @samp{foox} | |
581 | or @samp{barx}. | |
7015aca4 RS |
582 | |
583 | @item | |
1cd71ce0 RS |
584 | To enclose a complicated expression for the postfix operators @samp{*}, |
585 | @samp{+} and @samp{?} to operate on. Thus, @samp{ba\(na\)*} matches | |
a9f0a989 RS |
586 | @samp{ba}, @samp{bana}, @samp{banana}, @samp{bananana}, etc., with any |
587 | number (zero or more) of @samp{na} strings. | |
7015aca4 RS |
588 | |
589 | @item | |
2d06696f RS |
590 | To record a matched substring for future reference with |
591 | @samp{\@var{digit}} (see below). | |
7015aca4 RS |
592 | @end enumerate |
593 | ||
594 | This last application is not a consequence of the idea of a | |
2d06696f RS |
595 | parenthetical grouping; it is a separate feature that was assigned as a |
596 | second meaning to the same @samp{\( @dots{} \)} construct because, in | |
a39c2e0d | 597 | practice, there was usually no conflict between the two meanings. But |
2d06696f RS |
598 | occasionally there is a conflict, and that led to the introduction of |
599 | shy groups. | |
600 | ||
601 | @item \(?: @dots{} \) | |
602 | is the @dfn{shy group} construct. A shy group serves the first two | |
603 | purposes of an ordinary group (controlling the nesting of other | |
604 | operators), but it does not get a number, so you cannot refer back to | |
605 | its value with @samp{\@var{digit}}. | |
606 | ||
bcb6b6b8 | 607 | Shy groups are particularly useful for mechanically-constructed regular |
2d06696f RS |
608 | expressions because they can be added automatically without altering the |
609 | numbering of any ordinary, non-shy groups. | |
7015aca4 RS |
610 | |
611 | @item \@var{digit} | |
61cfa852 | 612 | matches the same text that matched the @var{digit}th occurrence of a |
a5d0a32e | 613 | grouping (@samp{\( @dots{} \)}) construct. |
7015aca4 | 614 | |
a5d0a32e RS |
615 | In other words, after the end of a group, the matcher remembers the |
616 | beginning and end of the text matched by that group. Later on in the | |
617 | regular expression you can use @samp{\} followed by @var{digit} to | |
618 | match that same text, whatever it may have been. | |
7015aca4 | 619 | |
a5d0a32e RS |
620 | The strings matching the first nine grouping constructs appearing in |
621 | the entire regular expression passed to a search or matching function | |
622 | are assigned numbers 1 through 9 in the order that the open | |
623 | parentheses appear in the regular expression. So you can use | |
624 | @samp{\1} through @samp{\9} to refer to the text matched by the | |
625 | corresponding grouping constructs. | |
7015aca4 RS |
626 | |
627 | For example, @samp{\(.*\)\1} matches any newline-free string that is | |
628 | composed of two identical halves. The @samp{\(.*\)} matches the first | |
629 | half, which may be anything, but the @samp{\1} that follows must match | |
630 | the same exact text. | |
631 | ||
bcb6b6b8 LT |
632 | If a @samp{\( @dots{} \)} construct matches more than once (which can |
633 | happen, for instance, if it is followed by @samp{*}), only the last | |
634 | match is recorded. | |
635 | ||
a5d0a32e RS |
636 | If a particular grouping construct in the regular expression was never |
637 | matched---for instance, if it appears inside of an alternative that | |
638 | wasn't used, or inside of a repetition that repeated zero times---then | |
639 | the corresponding @samp{\@var{digit}} construct never matches | |
640 | anything. To use an artificial example,, @samp{\(foo\(b*\)\|lose\)\2} | |
641 | cannot match @samp{lose}: the second alternative inside the larger | |
642 | group matches it, but then @samp{\2} is undefined and can't match | |
643 | anything. But it can match @samp{foobb}, because the first | |
644 | alternative matches @samp{foob} and @samp{\2} matches @samp{b}. | |
645 | ||
7015aca4 RS |
646 | @item \w |
647 | @cindex @samp{\w} in regexp | |
648 | matches any word-constituent character. The editor syntax table | |
649 | determines which characters these are. @xref{Syntax Tables}. | |
650 | ||
651 | @item \W | |
652 | @cindex @samp{\W} in regexp | |
61cfa852 | 653 | matches any character that is not a word constituent. |
7015aca4 RS |
654 | |
655 | @item \s@var{code} | |
656 | @cindex @samp{\s} in regexp | |
657 | matches any character whose syntax is @var{code}. Here @var{code} is a | |
61cfa852 | 658 | character that represents a syntax code: thus, @samp{w} for word |
7015aca4 | 659 | constituent, @samp{-} for whitespace, @samp{(} for open parenthesis, |
f9f59935 RS |
660 | etc. To represent whitespace syntax, use either @samp{-} or a space |
661 | character. @xref{Syntax Class Table}, for a list of syntax codes and | |
662 | the characters that stand for them. | |
7015aca4 RS |
663 | |
664 | @item \S@var{code} | |
665 | @cindex @samp{\S} in regexp | |
666 | matches any character whose syntax is not @var{code}. | |
a8b5bbef DL |
667 | |
668 | @item \c@var{c} | |
669 | matches any character whose category is @var{c}. Here @var{c} is a | |
670 | character that represents a category: thus, @samp{c} for Chinese | |
671 | characters or @samp{g} for Greek characters in the standard category | |
672 | table. | |
673 | ||
674 | @item \C@var{c} | |
675 | matches any character whose category is not @var{c}. | |
7015aca4 RS |
676 | @end table |
677 | ||
61cfa852 | 678 | The following regular expression constructs match the empty string---that is, |
7015aca4 | 679 | they don't use up any characters---but whether they match depends on the |
bcb6b6b8 LT |
680 | context. For all, the beginning and end of the accessible portion of |
681 | the buffer are treated as if they were the actual beginning and end of | |
682 | the buffer. | |
7015aca4 | 683 | |
969fe9b5 | 684 | @table @samp |
7015aca4 RS |
685 | @item \` |
686 | @cindex @samp{\`} in regexp | |
687 | matches the empty string, but only at the beginning | |
688 | of the buffer or string being matched against. | |
689 | ||
690 | @item \' | |
691 | @cindex @samp{\'} in regexp | |
692 | matches the empty string, but only at the end of | |
693 | the buffer or string being matched against. | |
694 | ||
695 | @item \= | |
696 | @cindex @samp{\=} in regexp | |
697 | matches the empty string, but only at point. | |
698 | (This construct is not defined when matching against a string.) | |
699 | ||
700 | @item \b | |
701 | @cindex @samp{\b} in regexp | |
702 | matches the empty string, but only at the beginning or | |
703 | end of a word. Thus, @samp{\bfoo\b} matches any occurrence of | |
704 | @samp{foo} as a separate word. @samp{\bballs?\b} matches | |
705 | @samp{ball} or @samp{balls} as a separate word.@refill | |
706 | ||
bcb6b6b8 | 707 | @samp{\b} matches at the beginning or end of the buffer (or string) |
1cd71ce0 RS |
708 | regardless of what text appears next to it. |
709 | ||
7015aca4 RS |
710 | @item \B |
711 | @cindex @samp{\B} in regexp | |
712 | matches the empty string, but @emph{not} at the beginning or | |
bcb6b6b8 | 713 | end of a word, nor at the beginning or end of the buffer (or string). |
7015aca4 RS |
714 | |
715 | @item \< | |
716 | @cindex @samp{\<} in regexp | |
717 | matches the empty string, but only at the beginning of a word. | |
bcb6b6b8 | 718 | @samp{\<} matches at the beginning of the buffer (or string) only if a |
1cd71ce0 | 719 | word-constituent character follows. |
7015aca4 RS |
720 | |
721 | @item \> | |
722 | @cindex @samp{\>} in regexp | |
1cd71ce0 | 723 | matches the empty string, but only at the end of a word. @samp{\>} |
bcb6b6b8 LT |
724 | matches at the end of the buffer (or string) only if the contents end |
725 | with a word-constituent character. | |
9a7e97c6 LT |
726 | |
727 | @item \_< | |
728 | @cindex @samp{\_<} in regexp | |
729 | matches the empty string, but only at the beginning of a symbol. A | |
730 | symbol is a sequence of one or more word or symbol constituent | |
731 | characters. @samp{\_<} matches at the beginning of the buffer (or | |
732 | string) only if a symbol-constituent character follows. | |
733 | ||
734 | @item \_> | |
735 | @cindex @samp{\_>} in regexp | |
736 | matches the empty string, but only at the end of a symbol. @samp{\_>} | |
737 | matches at the end of the buffer (or string) only if the contents end | |
738 | with a symbol-constituent character. | |
7015aca4 RS |
739 | @end table |
740 | ||
741 | @kindex invalid-regexp | |
742 | Not every string is a valid regular expression. For example, a string | |
743 | with unbalanced square brackets is invalid (with a few exceptions, such | |
61cfa852 | 744 | as @samp{[]]}), and so is a string that ends with a single @samp{\}. If |
7015aca4 RS |
745 | an invalid regular expression is passed to any of the search functions, |
746 | an @code{invalid-regexp} error is signaled. | |
747 | ||
7015aca4 RS |
748 | @node Regexp Example |
749 | @comment node-name, next, previous, up | |
750 | @subsection Complex Regexp Example | |
751 | ||
bcb6b6b8 LT |
752 | Here is a complicated regexp which was formerly used by Emacs to |
753 | recognize the end of a sentence together with any whitespace that | |
45fa30b2 LT |
754 | follows. (Nowadays Emacs uses a similar but more complex default |
755 | regexp constructed by the function @code{sentence-end}. | |
756 | @xref{Standard Regexps}.) | |
7015aca4 RS |
757 | |
758 | First, we show the regexp as a string in Lisp syntax to distinguish | |
759 | spaces from tab characters. The string constant begins and ends with a | |
760 | double-quote. @samp{\"} stands for a double-quote as part of the | |
761 | string, @samp{\\} for a backslash as part of the string, @samp{\t} for a | |
762 | tab and @samp{\n} for a newline. | |
763 | ||
764 | @example | |
bcb6b6b8 | 765 | "[.?!][]\"')@}]*\\($\\| $\\|\t\\|@ @ \\)[ \t\n]*" |
7015aca4 RS |
766 | @end example |
767 | ||
969fe9b5 | 768 | @noindent |
bcb6b6b8 | 769 | In contrast, if you evaluate this string, you will see the following: |
7015aca4 RS |
770 | |
771 | @example | |
772 | @group | |
bcb6b6b8 LT |
773 | "[.?!][]\"')@}]*\\($\\| $\\|\t\\|@ @ \\)[ \t\n]*" |
774 | @result{} "[.?!][]\"')@}]*\\($\\| $\\| \\|@ @ \\)[ | |
7015aca4 RS |
775 | ]*" |
776 | @end group | |
777 | @end example | |
778 | ||
779 | @noindent | |
780 | In this output, tab and newline appear as themselves. | |
781 | ||
782 | This regular expression contains four parts in succession and can be | |
783 | deciphered as follows: | |
784 | ||
785 | @table @code | |
786 | @item [.?!] | |
969fe9b5 RS |
787 | The first part of the pattern is a character alternative that matches |
788 | any one of three characters: period, question mark, and exclamation | |
bcb6b6b8 | 789 | mark. The match must begin with one of these three characters. (This |
45fa30b2 LT |
790 | is one point where the new default regexp used by Emacs differs from |
791 | the old. The new value also allows some non-@acronym{ASCII} | |
792 | characters that end a sentence without any following whitespace.) | |
7015aca4 RS |
793 | |
794 | @item []\"')@}]* | |
795 | The second part of the pattern matches any closing braces and quotation | |
796 | marks, zero or more of them, that may follow the period, question mark | |
797 | or exclamation mark. The @code{\"} is Lisp syntax for a double-quote in | |
798 | a string. The @samp{*} at the end indicates that the immediately | |
969fe9b5 | 799 | preceding regular expression (a character alternative, in this case) may be |
7015aca4 RS |
800 | repeated zero or more times. |
801 | ||
7fd1911a | 802 | @item \\($\\|@ $\\|\t\\|@ @ \\) |
7015aca4 | 803 | The third part of the pattern matches the whitespace that follows the |
f9f59935 RS |
804 | end of a sentence: the end of a line (optionally with a space), or a |
805 | tab, or two spaces. The double backslashes mark the parentheses and | |
806 | vertical bars as regular expression syntax; the parentheses delimit a | |
807 | group and the vertical bars separate alternatives. The dollar sign is | |
808 | used to match the end of a line. | |
7015aca4 RS |
809 | |
810 | @item [ \t\n]* | |
811 | Finally, the last part of the pattern matches any additional whitespace | |
812 | beyond the minimum needed to end a sentence. | |
813 | @end table | |
814 | ||
8241495d RS |
815 | @node Regexp Functions |
816 | @subsection Regular Expression Functions | |
817 | ||
818 | These functions operate on regular expressions. | |
819 | ||
820 | @defun regexp-quote string | |
821 | This function returns a regular expression whose only exact match is | |
822 | @var{string}. Using this regular expression in @code{looking-at} will | |
823 | succeed only if the next characters in the buffer are @var{string}; | |
824 | using it in a search function will succeed if the text being searched | |
825 | contains @var{string}. | |
826 | ||
827 | This allows you to request an exact string match or search when calling | |
828 | a function that wants a regular expression. | |
829 | ||
830 | @example | |
831 | @group | |
832 | (regexp-quote "^The cat$") | |
833 | @result{} "\\^The cat\\$" | |
834 | @end group | |
835 | @end example | |
836 | ||
837 | One use of @code{regexp-quote} is to combine an exact string match with | |
838 | context described as a regular expression. For example, this searches | |
839 | for the string that is the value of @var{string}, surrounded by | |
840 | whitespace: | |
841 | ||
842 | @example | |
843 | @group | |
844 | (re-search-forward | |
845 | (concat "\\s-" (regexp-quote string) "\\s-")) | |
846 | @end group | |
847 | @end example | |
848 | @end defun | |
849 | ||
850 | @defun regexp-opt strings &optional paren | |
8241495d | 851 | This function returns an efficient regular expression that will match |
bcb6b6b8 LT |
852 | any of the strings in the list @var{strings}. This is useful when you |
853 | need to make matching or searching as fast as possible---for example, | |
854 | for Font Lock mode. | |
8241495d RS |
855 | |
856 | If the optional argument @var{paren} is non-@code{nil}, then the | |
857 | returned regular expression is always enclosed by at least one | |
bcb6b6b8 LT |
858 | parentheses-grouping construct. If @var{paren} is @code{words}, then |
859 | that construct is additionally surrounded by @samp{\<} and @samp{\>}. | |
8241495d RS |
860 | |
861 | This simplified definition of @code{regexp-opt} produces a | |
862 | regular expression which is equivalent to the actual value | |
863 | (but not as efficient): | |
864 | ||
865 | @example | |
866 | (defun regexp-opt (strings paren) | |
867 | (let ((open-paren (if paren "\\(" "")) | |
868 | (close-paren (if paren "\\)" ""))) | |
869 | (concat open-paren | |
870 | (mapconcat 'regexp-quote strings "\\|") | |
871 | close-paren))) | |
872 | @end example | |
873 | @end defun | |
874 | ||
875 | @defun regexp-opt-depth regexp | |
8241495d | 876 | This function returns the total number of grouping constructs |
bcb6b6b8 LT |
877 | (parenthesized expressions) in @var{regexp}. (This does not include |
878 | shy groups.) | |
8241495d RS |
879 | @end defun |
880 | ||
7015aca4 RS |
881 | @node Regexp Search |
882 | @section Regular Expression Searching | |
883 | @cindex regular expression searching | |
884 | @cindex regexp searching | |
885 | @cindex searching for regexp | |
886 | ||
969fe9b5 RS |
887 | In GNU Emacs, you can search for the next match for a regular |
888 | expression either incrementally or not. For incremental search | |
889 | commands, see @ref{Regexp Search, , Regular Expression Search, emacs, | |
890 | The GNU Emacs Manual}. Here we describe only the search functions | |
891 | useful in programs. The principal one is @code{re-search-forward}. | |
7015aca4 | 892 | |
f9f59935 RS |
893 | These search functions convert the regular expression to multibyte if |
894 | the buffer is multibyte; they convert the regular expression to unibyte | |
895 | if the buffer is unibyte. @xref{Text Representations}. | |
896 | ||
7015aca4 RS |
897 | @deffn Command re-search-forward regexp &optional limit noerror repeat |
898 | This function searches forward in the current buffer for a string of | |
899 | text that is matched by the regular expression @var{regexp}. The | |
900 | function skips over any amount of text that is not matched by | |
901 | @var{regexp}, and leaves point at the end of the first match found. | |
902 | It returns the new value of point. | |
903 | ||
5bb8ca2a RS |
904 | If @var{limit} is non-@code{nil}, it must be a position in the current |
905 | buffer. It specifies the upper bound to the search. No match | |
906 | extending after that position is accepted. | |
7015aca4 | 907 | |
5bb8ca2a RS |
908 | If @var{repeat} is supplied, it must be a positive number; the search |
909 | is repeated that many times; each repetition starts at the end of the | |
4362c714 RS |
910 | previous match. If all these successive searches succeed, the search |
911 | succeeds, moving point and returning its new value. Otherwise the | |
912 | search fails. What @code{re-search-forward} does when the search | |
913 | fails depends on the value of @var{noerror}: | |
f9f59935 | 914 | |
4362c714 RS |
915 | @table @asis |
916 | @item @code{nil} | |
917 | Signal a @code{search-failed} error. | |
918 | @item @code{t} | |
919 | Do nothing and return @code{nil}. | |
920 | @item anything else | |
921 | Move point to @var{limit} (or the end of the accessible portion of the | |
922 | buffer) and return @code{nil}. | |
923 | @end table | |
7015aca4 | 924 | |
7015aca4 RS |
925 | In the following example, point is initially before the @samp{T}. |
926 | Evaluating the search call moves point to the end of that line (between | |
927 | the @samp{t} of @samp{hat} and the newline). | |
928 | ||
929 | @example | |
930 | @group | |
931 | ---------- Buffer: foo ---------- | |
932 | I read "@point{}The cat in the hat | |
933 | comes back" twice. | |
934 | ---------- Buffer: foo ---------- | |
935 | @end group | |
936 | ||
937 | @group | |
938 | (re-search-forward "[a-z]+" nil t 5) | |
939 | @result{} 27 | |
940 | ||
941 | ---------- Buffer: foo ---------- | |
942 | I read "The cat in the hat@point{} | |
943 | comes back" twice. | |
944 | ---------- Buffer: foo ---------- | |
945 | @end group | |
946 | @end example | |
947 | @end deffn | |
948 | ||
949 | @deffn Command re-search-backward regexp &optional limit noerror repeat | |
950 | This function searches backward in the current buffer for a string of | |
951 | text that is matched by the regular expression @var{regexp}, leaving | |
952 | point at the beginning of the first text found. | |
953 | ||
7fd1911a RS |
954 | This function is analogous to @code{re-search-forward}, but they are not |
955 | simple mirror images. @code{re-search-forward} finds the match whose | |
956 | beginning is as close as possible to the starting point. If | |
957 | @code{re-search-backward} were a perfect mirror image, it would find the | |
958 | match whose end is as close as possible. However, in fact it finds the | |
bcb6b6b8 LT |
959 | match whose beginning is as close as possible (and yet ends before the |
960 | starting point). The reason for this is that matching a regular | |
961 | expression at a given spot always works from beginning to end, and | |
962 | starts at a specified beginning position. | |
7015aca4 RS |
963 | |
964 | A true mirror-image of @code{re-search-forward} would require a special | |
969fe9b5 RS |
965 | feature for matching regular expressions from end to beginning. It's |
966 | not worth the trouble of implementing that. | |
7015aca4 RS |
967 | @end deffn |
968 | ||
969 | @defun string-match regexp string &optional start | |
970 | This function returns the index of the start of the first match for | |
971 | the regular expression @var{regexp} in @var{string}, or @code{nil} if | |
972 | there is no match. If @var{start} is non-@code{nil}, the search starts | |
973 | at that index in @var{string}. | |
974 | ||
975 | For example, | |
976 | ||
977 | @example | |
978 | @group | |
979 | (string-match | |
980 | "quick" "The quick brown fox jumped quickly.") | |
981 | @result{} 4 | |
982 | @end group | |
983 | @group | |
984 | (string-match | |
985 | "quick" "The quick brown fox jumped quickly." 8) | |
986 | @result{} 27 | |
987 | @end group | |
988 | @end example | |
989 | ||
990 | @noindent | |
991 | The index of the first character of the | |
992 | string is 0, the index of the second character is 1, and so on. | |
993 | ||
994 | After this function returns, the index of the first character beyond | |
995 | the match is available as @code{(match-end 0)}. @xref{Match Data}. | |
996 | ||
997 | @example | |
998 | @group | |
999 | (string-match | |
1000 | "quick" "The quick brown fox jumped quickly." 8) | |
1001 | @result{} 27 | |
1002 | @end group | |
1003 | ||
1004 | @group | |
1005 | (match-end 0) | |
1006 | @result{} 32 | |
1007 | @end group | |
1008 | @end example | |
1009 | @end defun | |
1010 | ||
1011 | @defun looking-at regexp | |
1012 | This function determines whether the text in the current buffer directly | |
1013 | following point matches the regular expression @var{regexp}. ``Directly | |
1014 | following'' means precisely that: the search is ``anchored'' and it can | |
1015 | succeed only starting with the first character following point. The | |
1016 | result is @code{t} if so, @code{nil} otherwise. | |
1017 | ||
1018 | This function does not move point, but it updates the match data, which | |
1019 | you can access using @code{match-beginning} and @code{match-end}. | |
1020 | @xref{Match Data}. | |
1021 | ||
1022 | In this example, point is located directly before the @samp{T}. If it | |
1023 | were anywhere else, the result would be @code{nil}. | |
1024 | ||
1025 | @example | |
1026 | @group | |
1027 | ---------- Buffer: foo ---------- | |
1028 | I read "@point{}The cat in the hat | |
1029 | comes back" twice. | |
1030 | ---------- Buffer: foo ---------- | |
1031 | ||
1032 | (looking-at "The cat in the hat$") | |
1033 | @result{} t | |
1034 | @end group | |
1035 | @end example | |
1036 | @end defun | |
1037 | ||
4d4d2d07 RS |
1038 | @defun looking-back regexp &optional limit |
1039 | This function returns @code{t} if @var{regexp} matches text before | |
1040 | point, ending at point, and @code{nil} otherwise. | |
1041 | ||
1042 | Because regular expression matching works only going forward, this is | |
1043 | implemented by searching backwards from point for a match that ends at | |
1044 | point. That can be quite slow if it has to search a long distance. | |
1045 | You can bound the time required by specifying @var{limit}, which says | |
1046 | not to search before @var{limit}. In this case, the match that is | |
1047 | found must begin at or after @var{limit}. | |
1048 | ||
1049 | @example | |
1050 | @group | |
1051 | ---------- Buffer: foo ---------- | |
1052 | I read "@point{}The cat in the hat | |
1053 | comes back" twice. | |
1054 | ---------- Buffer: foo ---------- | |
1055 | ||
1056 | (looking-back "read \"" 3) | |
1057 | @result{} t | |
1058 | (looking-back "read \"" 4) | |
1059 | @result{} nil | |
1060 | @end group | |
1061 | @end example | |
1062 | @end defun | |
1063 | ||
fe83e8de | 1064 | @defvar search-spaces-regexp |
65b65d26 RS |
1065 | If this variable is non-@code{nil}, it should be a regular expression |
1066 | that says how to search for whitespace. In that case, any group of | |
5bb8ca2a RS |
1067 | spaces in a regular expression being searched for stands for use of |
1068 | this regular expression. However, spaces inside of constructs such as | |
1069 | @samp{[@dots{}]} and @samp{*}, @samp{+}, @samp{?} are not affected by | |
1070 | @code{search-spaces-regexp}. | |
1071 | ||
1072 | Since this variable affects all regular expression search and match | |
1073 | constructs, you should bind it temporarily for as small as possible | |
1074 | a part of the code. | |
65b65d26 RS |
1075 | @end defvar |
1076 | ||
22697dac KH |
1077 | @node POSIX Regexps |
1078 | @section POSIX Regular Expression Searching | |
1079 | ||
1080 | The usual regular expression functions do backtracking when necessary | |
1081 | to handle the @samp{\|} and repetition constructs, but they continue | |
1082 | this only until they find @emph{some} match. Then they succeed and | |
1083 | report the first match found. | |
1084 | ||
1085 | This section describes alternative search functions which perform the | |
1086 | full backtracking specified by the POSIX standard for regular expression | |
1087 | matching. They continue backtracking until they have tried all | |
1088 | possibilities and found all matches, so they can report the longest | |
1089 | match, as required by POSIX. This is much slower, so use these | |
1090 | functions only when you really need the longest match. | |
1091 | ||
01913af2 RS |
1092 | The POSIX search and match functions do not properly support the |
1093 | non-greedy repetition operators. This is because POSIX backtracking | |
1094 | conflicts with the semantics of non-greedy repetition. | |
1095 | ||
22697dac KH |
1096 | @defun posix-search-forward regexp &optional limit noerror repeat |
1097 | This is like @code{re-search-forward} except that it performs the full | |
1098 | backtracking specified by the POSIX standard for regular expression | |
1099 | matching. | |
1100 | @end defun | |
1101 | ||
1102 | @defun posix-search-backward regexp &optional limit noerror repeat | |
1103 | This is like @code{re-search-backward} except that it performs the full | |
1104 | backtracking specified by the POSIX standard for regular expression | |
1105 | matching. | |
1106 | @end defun | |
1107 | ||
1108 | @defun posix-looking-at regexp | |
1109 | This is like @code{looking-at} except that it performs the full | |
1110 | backtracking specified by the POSIX standard for regular expression | |
1111 | matching. | |
1112 | @end defun | |
1113 | ||
1114 | @defun posix-string-match regexp string &optional start | |
1115 | This is like @code{string-match} except that it performs the full | |
1116 | backtracking specified by the POSIX standard for regular expression | |
1117 | matching. | |
1118 | @end defun | |
1119 | ||
7015aca4 RS |
1120 | @node Match Data |
1121 | @section The Match Data | |
1122 | @cindex match data | |
1123 | ||
3f63de1e | 1124 | Emacs keeps track of the start and end positions of the segments of |
99543e8b RS |
1125 | text found during a search; this is called the @dfn{match data}. |
1126 | Thanks to the match data, you can search for a complex pattern, such | |
1127 | as a date in a mail message, and then extract parts of the match under | |
1128 | control of the pattern. | |
7015aca4 RS |
1129 | |
1130 | Because the match data normally describe the most recent search only, | |
1131 | you must be careful not to do another search inadvertently between the | |
1132 | search you wish to refer back to and the use of the match data. If you | |
1133 | can't avoid another intervening search, you must save and restore the | |
1134 | match data around it, to prevent it from being overwritten. | |
1135 | ||
1136 | @menu | |
969fe9b5 | 1137 | * Replacing Match:: Replacing a substring that was matched. |
7015aca4 RS |
1138 | * Simple Match Data:: Accessing single items of match data, |
1139 | such as where a particular subexpression started. | |
7015aca4 RS |
1140 | * Entire Match Data:: Accessing the entire match data at once, as a list. |
1141 | * Saving Match Data:: Saving and restoring the match data. | |
1142 | @end menu | |
1143 | ||
969fe9b5 | 1144 | @node Replacing Match |
8241495d | 1145 | @subsection Replacing the Text that Matched |
969fe9b5 | 1146 | |
99543e8b RS |
1147 | This function replaces all or part of the text matched by the last |
1148 | search. It works by means of the match data. | |
969fe9b5 RS |
1149 | |
1150 | @cindex case in replacements | |
1151 | @defun replace-match replacement &optional fixedcase literal string subexp | |
1152 | This function replaces the text in the buffer (or in @var{string}) that | |
1153 | was matched by the last search. It replaces that text with | |
1154 | @var{replacement}. | |
1155 | ||
1156 | If you did the last search in a buffer, you should specify @code{nil} | |
bcb6b6b8 LT |
1157 | for @var{string} and make sure that the current buffer when you call |
1158 | @code{replace-match} is the one in which you did the searching or | |
1159 | matching. Then @code{replace-match} does the replacement by editing | |
1160 | the buffer; it leaves point at the end of the replacement text, and | |
1161 | returns @code{t}. | |
969fe9b5 RS |
1162 | |
1163 | If you did the search in a string, pass the same string as @var{string}. | |
1164 | Then @code{replace-match} does the replacement by constructing and | |
1165 | returning a new string. | |
1166 | ||
2037b263 RS |
1167 | If @var{fixedcase} is non-@code{nil}, then @code{replace-match} uses |
1168 | the replacement text without case conversion; otherwise, it converts | |
1169 | the replacement text depending upon the capitalization of the text to | |
1170 | be replaced. If the original text is all upper case, this converts | |
1171 | the replacement text to upper case. If all words of the original text | |
1172 | are capitalized, this capitalizes all the words of the replacement | |
1173 | text. If all the words are one-letter and they are all upper case, | |
1174 | they are treated as capitalized words rather than all-upper-case | |
1175 | words. | |
969fe9b5 | 1176 | |
969fe9b5 RS |
1177 | If @var{literal} is non-@code{nil}, then @var{replacement} is inserted |
1178 | exactly as it is, the only alterations being case changes as needed. | |
1179 | If it is @code{nil} (the default), then the character @samp{\} is treated | |
1180 | specially. If a @samp{\} appears in @var{replacement}, then it must be | |
1181 | part of one of the following sequences: | |
1182 | ||
1183 | @table @asis | |
1184 | @item @samp{\&} | |
1185 | @cindex @samp{&} in replacement | |
1186 | @samp{\&} stands for the entire text being replaced. | |
1187 | ||
1188 | @item @samp{\@var{n}} | |
1189 | @cindex @samp{\@var{n}} in replacement | |
1190 | @samp{\@var{n}}, where @var{n} is a digit, stands for the text that | |
1191 | matched the @var{n}th subexpression in the original regexp. | |
1192 | Subexpressions are those expressions grouped inside @samp{\(@dots{}\)}. | |
bcb6b6b8 | 1193 | If the @var{n}th subexpression never matched, an empty string is substituted. |
969fe9b5 RS |
1194 | |
1195 | @item @samp{\\} | |
1196 | @cindex @samp{\} in replacement | |
1197 | @samp{\\} stands for a single @samp{\} in the replacement text. | |
1198 | @end table | |
1199 | ||
2037b263 RS |
1200 | These substitutions occur after case conversion, if any, |
1201 | so the strings they substitute are never case-converted. | |
1202 | ||
969fe9b5 RS |
1203 | If @var{subexp} is non-@code{nil}, that says to replace just |
1204 | subexpression number @var{subexp} of the regexp that was matched, not | |
1205 | the entire match. For example, after matching @samp{foo \(ba*r\)}, | |
1206 | calling @code{replace-match} with 1 as @var{subexp} means to replace | |
1207 | just the text that matched @samp{\(ba*r\)}. | |
1208 | @end defun | |
1209 | ||
7015aca4 RS |
1210 | @node Simple Match Data |
1211 | @subsection Simple Match Data Access | |
1212 | ||
22697dac | 1213 | This section explains how to use the match data to find out what was |
87bf725e | 1214 | matched by the last search or match operation, if it succeeded. |
22697dac KH |
1215 | |
1216 | You can ask about the entire matching text, or about a particular | |
1217 | parenthetical subexpression of a regular expression. The @var{count} | |
1218 | argument in the functions below specifies which. If @var{count} is | |
1219 | zero, you are asking about the entire match. If @var{count} is | |
1220 | positive, it specifies which subexpression you want. | |
1221 | ||
1222 | Recall that the subexpressions of a regular expression are those | |
1223 | expressions grouped with escaped parentheses, @samp{\(@dots{}\)}. The | |
1224 | @var{count}th subexpression is found by counting occurrences of | |
1225 | @samp{\(} from the beginning of the whole regular expression. The first | |
1226 | subexpression is numbered 1, the second 2, and so on. Only regular | |
1227 | expressions can have subexpressions---after a simple string search, the | |
1228 | only information available is about the entire match. | |
1229 | ||
a9f0a989 RS |
1230 | A search which fails may or may not alter the match data. In the |
1231 | past, a failing search did not do this, but we may change it in the | |
87bf725e RS |
1232 | future. So don't try to rely on the value of the match data after |
1233 | a failing search. | |
a9f0a989 | 1234 | |
22697dac KH |
1235 | @defun match-string count &optional in-string |
1236 | This function returns, as a string, the text matched in the last search | |
1237 | or match operation. It returns the entire text if @var{count} is zero, | |
1238 | or just the portion corresponding to the @var{count}th parenthetical | |
a5d0a32e | 1239 | subexpression, if @var{count} is positive. |
22697dac KH |
1240 | |
1241 | If the last such operation was done against a string with | |
1242 | @code{string-match}, then you should pass the same string as the | |
969fe9b5 | 1243 | argument @var{in-string}. After a buffer search or match, |
22697dac KH |
1244 | you should omit @var{in-string} or pass @code{nil} for it; but you |
1245 | should make sure that the current buffer when you call | |
1246 | @code{match-string} is the one in which you did the searching or | |
1247 | matching. | |
a5d0a32e RS |
1248 | |
1249 | The value is @code{nil} if @var{count} is out of range, or for a | |
1250 | subexpression inside a @samp{\|} alternative that wasn't used or a | |
1251 | repetition that repeated zero times. | |
22697dac | 1252 | @end defun |
7015aca4 | 1253 | |
79ddc9c9 | 1254 | @defun match-string-no-properties count &optional in-string |
f9f59935 RS |
1255 | This function is like @code{match-string} except that the result |
1256 | has no text properties. | |
1257 | @end defun | |
1258 | ||
7015aca4 RS |
1259 | @defun match-beginning count |
1260 | This function returns the position of the start of text matched by the | |
1261 | last regular expression searched for, or a subexpression of it. | |
1262 | ||
7fd1911a | 1263 | If @var{count} is zero, then the value is the position of the start of |
eaac2be1 | 1264 | the entire match. Otherwise, @var{count} specifies a subexpression in |
969fe9b5 | 1265 | the regular expression, and the value of the function is the starting |
22697dac KH |
1266 | position of the match for that subexpression. |
1267 | ||
1268 | The value is @code{nil} for a subexpression inside a @samp{\|} | |
a5d0a32e | 1269 | alternative that wasn't used or a repetition that repeated zero times. |
7015aca4 RS |
1270 | @end defun |
1271 | ||
1272 | @defun match-end count | |
22697dac KH |
1273 | This function is like @code{match-beginning} except that it returns the |
1274 | position of the end of the match, rather than the position of the | |
1275 | beginning. | |
7015aca4 RS |
1276 | @end defun |
1277 | ||
1278 | Here is an example of using the match data, with a comment showing the | |
1279 | positions within the text: | |
1280 | ||
1281 | @example | |
1282 | @group | |
1283 | (string-match "\\(qu\\)\\(ick\\)" | |
1284 | "The quick fox jumped quickly.") | |
177c0ea7 | 1285 | ;0123456789 |
7015aca4 RS |
1286 | @result{} 4 |
1287 | @end group | |
1288 | ||
22697dac KH |
1289 | @group |
1290 | (match-string 0 "The quick fox jumped quickly.") | |
1291 | @result{} "quick" | |
1292 | (match-string 1 "The quick fox jumped quickly.") | |
1293 | @result{} "qu" | |
1294 | (match-string 2 "The quick fox jumped quickly.") | |
1295 | @result{} "ick" | |
1296 | @end group | |
1297 | ||
7015aca4 RS |
1298 | @group |
1299 | (match-beginning 1) ; @r{The beginning of the match} | |
1300 | @result{} 4 ; @r{with @samp{qu} is at index 4.} | |
1301 | @end group | |
1302 | ||
1303 | @group | |
1304 | (match-beginning 2) ; @r{The beginning of the match} | |
1305 | @result{} 6 ; @r{with @samp{ick} is at index 6.} | |
1306 | @end group | |
1307 | ||
1308 | @group | |
1309 | (match-end 1) ; @r{The end of the match} | |
1310 | @result{} 6 ; @r{with @samp{qu} is at index 6.} | |
1311 | ||
1312 | (match-end 2) ; @r{The end of the match} | |
1313 | @result{} 9 ; @r{with @samp{ick} is at index 9.} | |
1314 | @end group | |
1315 | @end example | |
1316 | ||
1317 | Here is another example. Point is initially located at the beginning | |
1318 | of the line. Searching moves point to between the space and the word | |
1319 | @samp{in}. The beginning of the entire match is at the 9th character of | |
1320 | the buffer (@samp{T}), and the beginning of the match for the first | |
1321 | subexpression is at the 13th character (@samp{c}). | |
1322 | ||
1323 | @example | |
1324 | @group | |
1325 | (list | |
1326 | (re-search-forward "The \\(cat \\)") | |
1327 | (match-beginning 0) | |
1328 | (match-beginning 1)) | |
7fd1911a | 1329 | @result{} (9 9 13) |
7015aca4 RS |
1330 | @end group |
1331 | ||
1332 | @group | |
1333 | ---------- Buffer: foo ---------- | |
1334 | I read "The cat @point{}in the hat comes back" twice. | |
1335 | ^ ^ | |
1336 | 9 13 | |
1337 | ---------- Buffer: foo ---------- | |
1338 | @end group | |
1339 | @end example | |
1340 | ||
1341 | @noindent | |
1342 | (In this case, the index returned is a buffer position; the first | |
1343 | character of the buffer counts as 1.) | |
1344 | ||
7015aca4 RS |
1345 | @node Entire Match Data |
1346 | @subsection Accessing the Entire Match Data | |
1347 | ||
1348 | The functions @code{match-data} and @code{set-match-data} read or | |
1349 | write the entire match data, all at once. | |
1350 | ||
4e370af2 | 1351 | @defun match-data &optional integers reuse reseat |
8135a25a RS |
1352 | This function returns a list of positions (markers or integers) that |
1353 | record all the information on what text the last search matched. | |
1354 | Element zero is the position of the beginning of the match for the | |
1355 | whole expression; element one is the position of the end of the match | |
1356 | for the expression. The next two elements are the positions of the | |
1357 | beginning and end of the match for the first subexpression, and so on. | |
1358 | In general, element | |
37680279 | 1359 | @ifnottex |
7015aca4 | 1360 | number 2@var{n} |
37680279 | 1361 | @end ifnottex |
7015aca4 RS |
1362 | @tex |
1363 | number {\mathsurround=0pt $2n$} | |
1364 | @end tex | |
1365 | corresponds to @code{(match-beginning @var{n})}; and | |
1366 | element | |
37680279 | 1367 | @ifnottex |
7015aca4 | 1368 | number 2@var{n} + 1 |
37680279 | 1369 | @end ifnottex |
7015aca4 RS |
1370 | @tex |
1371 | number {\mathsurround=0pt $2n+1$} | |
1372 | @end tex | |
1373 | corresponds to @code{(match-end @var{n})}. | |
1374 | ||
8135a25a RS |
1375 | Normally all the elements are markers or @code{nil}, but if |
1376 | @var{integers} is non-@code{nil}, that means to use integers instead | |
1377 | of markers. (In that case, the buffer itself is appended as an | |
1378 | additional element at the end of the list, to facilitate complete | |
1379 | restoration of the match data.) If the last match was done on a | |
1380 | string with @code{string-match}, then integers are always used, | |
1381 | since markers can't point into a string. | |
bcb6b6b8 LT |
1382 | |
1383 | If @var{reuse} is non-@code{nil}, it should be a list. In that case, | |
1384 | @code{match-data} stores the match data in @var{reuse}. That is, | |
1385 | @var{reuse} is destructively modified. @var{reuse} does not need to | |
1386 | have the right length. If it is not long enough to contain the match | |
1387 | data, it is extended. If it is too long, the length of @var{reuse} | |
1388 | stays the same, but the elements that were not used are set to | |
8135a25a RS |
1389 | @code{nil}. The purpose of this feature is to reduce the need for |
1390 | garbage collection. | |
7015aca4 | 1391 | |
4e370af2 | 1392 | If @var{reseat} is non-@code{nil}, all markers on the @var{reuse} list |
68be435e | 1393 | are reseated to point to nowhere. |
4e370af2 | 1394 | |
7015aca4 RS |
1395 | As always, there must be no possibility of intervening searches between |
1396 | the call to a search function and the call to @code{match-data} that is | |
1397 | intended to access the match data for that search. | |
1398 | ||
1399 | @example | |
1400 | @group | |
1401 | (match-data) | |
1402 | @result{} (#<marker at 9 in foo> | |
1403 | #<marker at 17 in foo> | |
1404 | #<marker at 13 in foo> | |
1405 | #<marker at 17 in foo>) | |
1406 | @end group | |
1407 | @end example | |
1408 | @end defun | |
1409 | ||
4e370af2 | 1410 | @defun set-match-data match-list &optional reseat |
7015aca4 RS |
1411 | This function sets the match data from the elements of @var{match-list}, |
1412 | which should be a list that was the value of a previous call to | |
3ab8acb9 RS |
1413 | @code{match-data}. (More precisely, anything that has the same format |
1414 | will work.) | |
7015aca4 RS |
1415 | |
1416 | If @var{match-list} refers to a buffer that doesn't exist, you don't get | |
1417 | an error; that sets the match data in a meaningless but harmless way. | |
1418 | ||
4e370af2 | 1419 | If @var{reseat} is non-@code{nil}, all markers on the @var{match-list} list |
68be435e | 1420 | are reseated to point to nowhere. |
4e370af2 | 1421 | |
7015aca4 | 1422 | @findex store-match-data |
969fe9b5 | 1423 | @code{store-match-data} is a semi-obsolete alias for @code{set-match-data}. |
7015aca4 RS |
1424 | @end defun |
1425 | ||
1426 | @node Saving Match Data | |
1427 | @subsection Saving and Restoring the Match Data | |
1428 | ||
d1280259 RS |
1429 | When you call a function that may do a search, you may need to save |
1430 | and restore the match data around that call, if you want to preserve the | |
1431 | match data from an earlier search for later use. Here is an example | |
1432 | that shows the problem that arises if you fail to save the match data: | |
7015aca4 RS |
1433 | |
1434 | @example | |
1435 | @group | |
1436 | (re-search-forward "The \\(cat \\)") | |
1437 | @result{} 48 | |
1438 | (foo) ; @r{Perhaps @code{foo} does} | |
1439 | ; @r{more searching.} | |
1440 | (match-end 0) | |
1441 | @result{} 61 ; @r{Unexpected result---not 48!} | |
1442 | @end group | |
1443 | @end example | |
1444 | ||
d1280259 | 1445 | You can save and restore the match data with @code{save-match-data}: |
7015aca4 | 1446 | |
bfe721d1 | 1447 | @defmac save-match-data body@dots{} |
1911e6e5 | 1448 | This macro executes @var{body}, saving and restoring the match |
bcb6b6b8 LT |
1449 | data around it. The return value is the value of the last form in |
1450 | @var{body}. | |
bfe721d1 | 1451 | @end defmac |
7015aca4 | 1452 | |
969fe9b5 RS |
1453 | You could use @code{set-match-data} together with @code{match-data} to |
1454 | imitate the effect of the special form @code{save-match-data}. Here is | |
1455 | how: | |
7015aca4 RS |
1456 | |
1457 | @example | |
1458 | @group | |
1459 | (let ((data (match-data))) | |
1460 | (unwind-protect | |
f9f59935 | 1461 | @dots{} ; @r{Ok to change the original match data.} |
7015aca4 RS |
1462 | (set-match-data data))) |
1463 | @end group | |
1464 | @end example | |
1465 | ||
d1280259 RS |
1466 | Emacs automatically saves and restores the match data when it runs |
1467 | process filter functions (@pxref{Filter Functions}) and process | |
1468 | sentinels (@pxref{Sentinels}). | |
1469 | ||
7015aca4 RS |
1470 | @ignore |
1471 | Here is a function which restores the match data provided the buffer | |
1472 | associated with it still exists. | |
1473 | ||
1474 | @smallexample | |
1475 | @group | |
1476 | (defun restore-match-data (data) | |
1477 | @c It is incorrect to split the first line of a doc string. | |
1478 | @c If there's a problem here, it should be solved in some other way. | |
1479 | "Restore the match data DATA unless the buffer is missing." | |
1480 | (catch 'foo | |
1481 | (let ((d data)) | |
1482 | @end group | |
1483 | (while d | |
1484 | (and (car d) | |
1485 | (null (marker-buffer (car d))) | |
1486 | @group | |
1487 | ;; @file{match-data} @r{buffer is deleted.} | |
1488 | (throw 'foo nil)) | |
1489 | (setq d (cdr d))) | |
1490 | (set-match-data data)))) | |
1491 | @end group | |
1492 | @end smallexample | |
1493 | @end ignore | |
1494 | ||
99543e8b RS |
1495 | @node Search and Replace |
1496 | @section Search and Replace | |
1497 | @cindex replacement | |
7015aca4 | 1498 | |
99543e8b RS |
1499 | If you want to find all matches for a regexp in part of the buffer, |
1500 | and replace them, the best way is to write an explicit loop using | |
1501 | @code{re-search-forward} and @code{replace-match}, like this: | |
7015aca4 | 1502 | |
99543e8b RS |
1503 | @example |
1504 | (while (re-search-forward "foo[ \t]+bar" nil t) | |
1505 | (replace-match "foobar")) | |
1506 | @end example | |
7015aca4 | 1507 | |
99543e8b RS |
1508 | @noindent |
1509 | @xref{Replacing Match,, Replacing the Text that Matched}, for a | |
1510 | description of @code{replace-match}. | |
7015aca4 | 1511 | |
99543e8b RS |
1512 | However, replacing matches in a string is more complex, especially |
1513 | if you want to do it efficiently. So Emacs provides a function to do | |
1514 | this. | |
7fd1911a | 1515 | |
99543e8b RS |
1516 | @defun replace-regexp-in-string regexp rep string &optional fixedcase literal subexp start |
1517 | This function copies @var{string} and searches it for matches for | |
1518 | @var{regexp}, and replaces them with @var{rep}. It returns the | |
1519 | modified copy. If @var{start} is non-@code{nil}, the search for | |
1520 | matches starts at that index in @var{string}, so matches starting | |
1521 | before that index are not changed. | |
7015aca4 | 1522 | |
99543e8b RS |
1523 | This function uses @code{replace-match} to do the replacement, and it |
1524 | passes the optional arguments @var{fixedcase}, @var{literal} and | |
1525 | @var{subexp} along to @code{replace-match}. | |
7015aca4 | 1526 | |
99543e8b RS |
1527 | Instead of a string, @var{rep} can be a function. In that case, |
1528 | @code{replace-regexp-in-string} calls @var{rep} for each match, | |
1529 | passing the text of the match as its sole argument. It collects the | |
1530 | value @var{rep} returns and passes that to @code{replace-match} as the | |
1531 | replacement string. The match-data at this point are the result | |
1532 | of matching @var{regexp} against a substring of @var{string}. | |
1533 | @end defun | |
1534 | ||
1535 | If you want to write a command along the lines of @code{query-replace}, | |
1536 | you can use @code{perform-replace} to do the work. | |
1537 | ||
1538 | @defun perform-replace from-string replacements query-flag regexp-flag delimited-flag &optional repeat-count map start end | |
1539 | This function is the guts of @code{query-replace} and related | |
1540 | commands. It searches for occurrences of @var{from-string} in the | |
1541 | text between positions @var{start} and @var{end} and replaces some or | |
1542 | all of them. If @var{start} is @code{nil} (or omitted), point is used | |
1543 | instead, and the end of the buffer's accessible portion is used for | |
1544 | @var{end}. | |
1545 | ||
1546 | If @var{query-flag} is @code{nil}, it replaces all | |
1547 | occurrences; otherwise, it asks the user what to do about each one. | |
1548 | ||
1549 | If @var{regexp-flag} is non-@code{nil}, then @var{from-string} is | |
1550 | considered a regular expression; otherwise, it must match literally. If | |
1551 | @var{delimited-flag} is non-@code{nil}, then only replacements | |
1552 | surrounded by word boundaries are considered. | |
1553 | ||
1554 | The argument @var{replacements} specifies what to replace occurrences | |
1555 | with. If it is a string, that string is used. It can also be a list of | |
1556 | strings, to be used in cyclic order. | |
1557 | ||
1558 | If @var{replacements} is a cons cell, @code{(@var{function} | |
1559 | . @var{data})}, this means to call @var{function} after each match to | |
1560 | get the replacement text. This function is called with two arguments: | |
1561 | @var{data}, and the number of replacements already made. | |
1562 | ||
1563 | If @var{repeat-count} is non-@code{nil}, it should be an integer. Then | |
1564 | it specifies how many times to use each of the strings in the | |
1565 | @var{replacements} list before advancing cyclically to the next one. | |
1566 | ||
1567 | If @var{from-string} contains upper-case letters, then | |
1568 | @code{perform-replace} binds @code{case-fold-search} to @code{nil}, and | |
1569 | it uses the @code{replacements} without altering the case of them. | |
1570 | ||
1571 | Normally, the keymap @code{query-replace-map} defines the possible | |
1572 | user responses for queries. The argument @var{map}, if | |
1573 | non-@code{nil}, specifies a keymap to use instead of | |
1574 | @code{query-replace-map}. | |
1575 | @end defun | |
1576 | ||
1577 | @defvar query-replace-map | |
1578 | This variable holds a special keymap that defines the valid user | |
1579 | responses for @code{perform-replace} and the commands that use it, as | |
1580 | well as @code{y-or-n-p} and @code{map-y-or-n-p}. This map is unusual | |
1581 | in two ways: | |
1582 | ||
1583 | @itemize @bullet | |
1584 | @item | |
1585 | The ``key bindings'' are not commands, just symbols that are meaningful | |
1586 | to the functions that use this map. | |
1587 | ||
1588 | @item | |
1589 | Prefix keys are not supported; each key binding must be for a | |
1590 | single-event key sequence. This is because the functions don't use | |
1591 | @code{read-key-sequence} to get the input; instead, they read a single | |
1592 | event and look it up ``by hand.'' | |
1593 | @end itemize | |
7015aca4 RS |
1594 | @end defvar |
1595 | ||
99543e8b RS |
1596 | Here are the meaningful ``bindings'' for @code{query-replace-map}. |
1597 | Several of them are meaningful only for @code{query-replace} and | |
1598 | friends. | |
1599 | ||
1600 | @table @code | |
1601 | @item act | |
1602 | Do take the action being considered---in other words, ``yes.'' | |
1603 | ||
1604 | @item skip | |
1605 | Do not take action for this question---in other words, ``no.'' | |
1606 | ||
1607 | @item exit | |
1608 | Answer this question ``no,'' and give up on the entire series of | |
1609 | questions, assuming that the answers will be ``no.'' | |
1610 | ||
1611 | @item act-and-exit | |
1612 | Answer this question ``yes,'' and give up on the entire series of | |
1613 | questions, assuming that subsequent answers will be ``no.'' | |
1614 | ||
1615 | @item act-and-show | |
1616 | Answer this question ``yes,'' but show the results---don't advance yet | |
1617 | to the next question. | |
1618 | ||
1619 | @item automatic | |
1620 | Answer this question and all subsequent questions in the series with | |
1621 | ``yes,'' without further user interaction. | |
1622 | ||
1623 | @item backup | |
1624 | Move back to the previous place that a question was asked about. | |
1625 | ||
1626 | @item edit | |
1627 | Enter a recursive edit to deal with this question---instead of any | |
1628 | other action that would normally be taken. | |
1629 | ||
1630 | @item delete-and-edit | |
1631 | Delete the text being considered, then enter a recursive edit to replace | |
1632 | it. | |
1633 | ||
1634 | @item recenter | |
1635 | Redisplay and center the window, then ask the same question again. | |
1636 | ||
1637 | @item quit | |
1638 | Perform a quit right away. Only @code{y-or-n-p} and related functions | |
1639 | use this answer. | |
1640 | ||
1641 | @item help | |
1642 | Display some help, then ask again. | |
1643 | @end table | |
1644 | ||
7015aca4 RS |
1645 | @node Standard Regexps |
1646 | @section Standard Regular Expressions Used in Editing | |
1647 | @cindex regexps used standardly in editing | |
1648 | @cindex standard regexps used in editing | |
1649 | ||
1650 | This section describes some variables that hold regular expressions | |
1651 | used for certain purposes in editing: | |
1652 | ||
1653 | @defvar page-delimiter | |
969fe9b5 RS |
1654 | This is the regular expression describing line-beginnings that separate |
1655 | pages. The default value is @code{"^\014"} (i.e., @code{"^^L"} or | |
1656 | @code{"^\C-l"}); this matches a line that starts with a formfeed | |
1657 | character. | |
7015aca4 RS |
1658 | @end defvar |
1659 | ||
22697dac KH |
1660 | The following two regular expressions should @emph{not} assume the |
1661 | match always starts at the beginning of a line; they should not use | |
1662 | @samp{^} to anchor the match. Most often, the paragraph commands do | |
1663 | check for a match only at the beginning of a line, which means that | |
bfe721d1 KH |
1664 | @samp{^} would be superfluous. When there is a nonzero left margin, |
1665 | they accept matches that start after the left margin. In that case, a | |
1666 | @samp{^} would be incorrect. However, a @samp{^} is harmless in modes | |
1667 | where a left margin is never used. | |
22697dac | 1668 | |
7015aca4 RS |
1669 | @defvar paragraph-separate |
1670 | This is the regular expression for recognizing the beginning of a line | |
1671 | that separates paragraphs. (If you change this, you may have to | |
7fd1911a | 1672 | change @code{paragraph-start} also.) The default value is |
22697dac KH |
1673 | @w{@code{"[@ \t\f]*$"}}, which matches a line that consists entirely of |
1674 | spaces, tabs, and form feeds (after its left margin). | |
7015aca4 RS |
1675 | @end defvar |
1676 | ||
1677 | @defvar paragraph-start | |
1678 | This is the regular expression for recognizing the beginning of a line | |
1679 | that starts @emph{or} separates paragraphs. The default value is | |
bcb6b6b8 LT |
1680 | @w{@code{"\f\\|[ \t]*$"}}, which matches a line containing only |
1681 | whitespace or starting with a form feed (after its left margin). | |
7015aca4 RS |
1682 | @end defvar |
1683 | ||
1684 | @defvar sentence-end | |
45fa30b2 LT |
1685 | If non-@code{nil}, the value should be a regular expression describing |
1686 | the end of a sentence, including the whitespace following the | |
1687 | sentence. (All paragraph boundaries also end sentences, regardless.) | |
1688 | ||
1689 | If the value is @code{nil}, the default, then the function | |
1690 | @code{sentence-end} has to construct the regexp. That is why you | |
1691 | should always call the function @code{sentence-end} to obtain the | |
1692 | regexp to be used to recognize the end of a sentence. | |
7015aca4 | 1693 | @end defvar |
ab5796a9 | 1694 | |
45fa30b2 LT |
1695 | @defun sentence-end |
1696 | This function returns the value of the variable @code{sentence-end}, | |
1697 | if non-@code{nil}. Otherwise it returns a default value based on the | |
1698 | values of the variables @code{sentence-end-double-space} | |
1699 | (@pxref{Definition of sentence-end-double-space}), | |
1700 | @code{sentence-end-without-period} and | |
1701 | @code{sentence-end-without-space}. | |
1702 | @end defun | |
1703 | ||
ab5796a9 MB |
1704 | @ignore |
1705 | arch-tag: c2573ca2-18aa-4839-93b8-924043ef831f | |
1706 | @end ignore |