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