| 1 | @c -*-texinfo-*- |
| 2 | @c This is part of the GNU Emacs Lisp Reference Manual. |
| 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2002, 2003, |
| 4 | @c 2004, 2005, 2006 Free Software Foundation, Inc. |
| 5 | @c See the file elisp.texi for copying conditions. |
| 6 | @setfilename ../info/searching |
| 7 | @node Searching and Matching, Syntax Tables, Non-ASCII Characters, Top |
| 8 | @chapter Searching and Matching |
| 9 | @cindex searching |
| 10 | |
| 11 | GNU Emacs provides two ways to search through a buffer for specified |
| 12 | text: exact string searches and regular expression searches. After a |
| 13 | regular expression search, you can examine the @dfn{match data} to |
| 14 | determine which text matched the whole regular expression or various |
| 15 | portions of it. |
| 16 | |
| 17 | @menu |
| 18 | * String Search:: Search for an exact match. |
| 19 | * Searching and Case:: Case-independent or case-significant searching. |
| 20 | * Regular Expressions:: Describing classes of strings. |
| 21 | * Regexp Search:: Searching for a match for a regexp. |
| 22 | * POSIX Regexps:: Searching POSIX-style for the longest match. |
| 23 | * Match Data:: Finding out which part of the text matched, |
| 24 | after a string or regexp search. |
| 25 | * Search and Replace:: Commands that loop, searching and replacing. |
| 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 |
| 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. |
| 41 | |
| 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 | |
| 46 | @deffn Command search-forward string &optional limit noerror repeat |
| 47 | This function searches forward from point for an exact match for |
| 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 | |
| 53 | In the following example, point is initially at the beginning of the |
| 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 | |
| 74 | The argument @var{limit} specifies the upper bound to the search. (It |
| 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 |
| 80 | What happens when the search fails depends on the value of |
| 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 |
| 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}.) |
| 88 | |
| 89 | The argument @var{noerror} only affects valid searches which fail to |
| 90 | find a match. Invalid arguments cause errors regardless of |
| 91 | @var{noerror}. |
| 92 | |
| 93 | If @var{repeat} is supplied (it must be a positive number), then the |
| 94 | search is repeated that many times (each time starting at the end of the |
| 95 | previous time's match). If these successive searches succeed, the |
| 96 | function succeeds, moving point and returning its new value. Otherwise |
| 97 | the search fails, with results depending on the value of |
| 98 | @var{noerror}, as described above. |
| 99 | @end deffn |
| 100 | |
| 101 | @deffn Command search-backward string &optional limit noerror repeat |
| 102 | This function searches backward from point for @var{string}. It is |
| 103 | just like @code{search-forward} except that it searches backwards and |
| 104 | leaves point at the beginning of the match. |
| 105 | @end deffn |
| 106 | |
| 107 | @deffn Command word-search-forward string &optional limit noerror repeat |
| 108 | @cindex word search |
| 109 | This function searches forward from point for a ``word'' match for |
| 110 | @var{string}. If it finds a match, it sets point to the end of the |
| 111 | match found, and returns the new value of point. |
| 112 | @c Emacs 19 feature |
| 113 | |
| 114 | Word matching regards @var{string} as a sequence of words, disregarding |
| 115 | punctuation that separates them. It searches the buffer for the same |
| 116 | sequence of words. Each word must be distinct in the buffer (searching |
| 117 | for the word @samp{ball} does not match the word @samp{balls}), but the |
| 118 | details of punctuation and spacing are ignored (searching for @samp{ball |
| 119 | boy} does match @samp{ball. Boy!}). |
| 120 | |
| 121 | In this example, point is initially at the beginning of the buffer; the |
| 122 | search leaves it between the @samp{y} and the @samp{!}. |
| 123 | |
| 124 | @example |
| 125 | @group |
| 126 | ---------- Buffer: foo ---------- |
| 127 | @point{}He said "Please! Find |
| 128 | the ball boy!" |
| 129 | ---------- Buffer: foo ---------- |
| 130 | @end group |
| 131 | |
| 132 | @group |
| 133 | (word-search-forward "Please find the ball, boy.") |
| 134 | @result{} 35 |
| 135 | |
| 136 | ---------- Buffer: foo ---------- |
| 137 | He said "Please! Find |
| 138 | the ball boy@point{}!" |
| 139 | ---------- Buffer: foo ---------- |
| 140 | @end group |
| 141 | @end example |
| 142 | |
| 143 | If @var{limit} is non-@code{nil}, it must be a position in the current |
| 144 | buffer; it specifies the upper bound to the search. The match found |
| 145 | must not extend after that position. |
| 146 | |
| 147 | If @var{noerror} is @code{nil}, then @code{word-search-forward} signals |
| 148 | an error if the search fails. If @var{noerror} is @code{t}, then it |
| 149 | returns @code{nil} instead of signaling an error. If @var{noerror} is |
| 150 | neither @code{nil} nor @code{t}, it moves point to @var{limit} (or the |
| 151 | end of the accessible portion of the buffer) and returns @code{nil}. |
| 152 | |
| 153 | If @var{repeat} is non-@code{nil}, then the search is repeated that many |
| 154 | times. Point is positioned at the end of the last match. |
| 155 | @end deffn |
| 156 | |
| 157 | @deffn Command word-search-backward string &optional limit noerror repeat |
| 158 | This function searches backward from point for a word match to |
| 159 | @var{string}. This function is just like @code{word-search-forward} |
| 160 | except that it searches backward and normally leaves point at the |
| 161 | beginning of the match. |
| 162 | @end deffn |
| 163 | |
| 164 | @node Searching and Case |
| 165 | @section Searching and Case |
| 166 | @cindex searching and case |
| 167 | |
| 168 | By default, searches in Emacs ignore the case of the text they are |
| 169 | searching through; if you specify searching for @samp{FOO}, then |
| 170 | @samp{Foo} or @samp{foo} is also considered a match. This applies to |
| 171 | regular expressions, too; thus, @samp{[aB]} would match @samp{a} or |
| 172 | @samp{A} or @samp{b} or @samp{B}. |
| 173 | |
| 174 | If you do not want this feature, set the variable |
| 175 | @code{case-fold-search} to @code{nil}. Then all letters must match |
| 176 | exactly, including case. This is a buffer-local variable; altering the |
| 177 | variable affects only the current buffer. (@xref{Intro to |
| 178 | Buffer-Local}.) Alternatively, you may change the value of |
| 179 | @code{default-case-fold-search}, which is the default value of |
| 180 | @code{case-fold-search} for buffers that do not override it. |
| 181 | |
| 182 | Note that the user-level incremental search feature handles case |
| 183 | distinctions differently. When given a lower case letter, it looks for |
| 184 | a match of either case, but when given an upper case letter, it looks |
| 185 | for an upper case letter only. But this has nothing to do with the |
| 186 | searching functions used in Lisp code. |
| 187 | |
| 188 | @defopt case-replace |
| 189 | This variable determines whether the higher level replacement |
| 190 | functions should preserve case. If the variable is @code{nil}, that |
| 191 | means to use the replacement text verbatim. A non-@code{nil} value |
| 192 | means to convert the case of the replacement text according to the |
| 193 | text being replaced. |
| 194 | |
| 195 | This variable is used by passing it as an argument to the function |
| 196 | @code{replace-match}. @xref{Replacing Match}. |
| 197 | @end defopt |
| 198 | |
| 199 | @defopt case-fold-search |
| 200 | This buffer-local variable determines whether searches should ignore |
| 201 | case. If the variable is @code{nil} they do not ignore case; otherwise |
| 202 | they do ignore case. |
| 203 | @end defopt |
| 204 | |
| 205 | @defvar default-case-fold-search |
| 206 | The value of this variable is the default value for |
| 207 | @code{case-fold-search} in buffers that do not override it. This is the |
| 208 | same as @code{(default-value 'case-fold-search)}. |
| 209 | @end defvar |
| 210 | |
| 211 | @node Regular Expressions |
| 212 | @section Regular Expressions |
| 213 | @cindex regular expression |
| 214 | @cindex regexp |
| 215 | |
| 216 | A @dfn{regular expression} (@dfn{regexp}, for short) is a pattern that |
| 217 | denotes a (possibly infinite) set of strings. Searching for matches for |
| 218 | a regexp is a very powerful operation. This section explains how to write |
| 219 | regexps; the following section says how to search for them. |
| 220 | |
| 221 | @findex re-builder |
| 222 | @cindex authoring regular expressions |
| 223 | For convenient interactive development of regular expressions, you |
| 224 | can use the @kbd{M-x re-builder} command. It provides a convenient |
| 225 | interface for creating regular expressions, by giving immediate visual |
| 226 | feedback in a separate buffer. As you edit the regexp, all its |
| 227 | matches in the target buffer are highlighted. Each parenthesized |
| 228 | sub-expression of the regexp is shown in a distinct face, which makes |
| 229 | it easier to verify even very complex regexps. |
| 230 | |
| 231 | @menu |
| 232 | * Syntax of Regexps:: Rules for writing regular expressions. |
| 233 | * Regexp Example:: Illustrates regular expression syntax. |
| 234 | * Regexp Functions:: Functions for operating on regular expressions. |
| 235 | @end menu |
| 236 | |
| 237 | @node Syntax of Regexps |
| 238 | @subsection Syntax of Regular Expressions |
| 239 | |
| 240 | Regular expressions have a syntax in which a few characters are |
| 241 | special constructs and the rest are @dfn{ordinary}. An ordinary |
| 242 | character is a simple regular expression that matches that character |
| 243 | and nothing else. The special characters are @samp{.}, @samp{*}, |
| 244 | @samp{+}, @samp{?}, @samp{[}, @samp{^}, @samp{$}, and @samp{\}; no new |
| 245 | special characters will be defined in the future. The character |
| 246 | @samp{]} is special if it ends a character alternative (see later). |
| 247 | The character @samp{-} is special inside a character alternative. A |
| 248 | @samp{[:} and balancing @samp{:]} enclose a character class inside a |
| 249 | character alternative. Any other character appearing in a regular |
| 250 | expression is ordinary, unless a @samp{\} precedes it. |
| 251 | |
| 252 | For example, @samp{f} is not a special character, so it is ordinary, and |
| 253 | therefore @samp{f} is a regular expression that matches the string |
| 254 | @samp{f} and no other string. (It does @emph{not} match the string |
| 255 | @samp{fg}, but it does match a @emph{part} of that string.) Likewise, |
| 256 | @samp{o} is a regular expression that matches only @samp{o}.@refill |
| 257 | |
| 258 | Any two regular expressions @var{a} and @var{b} can be concatenated. The |
| 259 | result is a regular expression that matches a string if @var{a} matches |
| 260 | some amount of the beginning of that string and @var{b} matches the rest of |
| 261 | the string.@refill |
| 262 | |
| 263 | As a simple example, we can concatenate the regular expressions @samp{f} |
| 264 | and @samp{o} to get the regular expression @samp{fo}, which matches only |
| 265 | the string @samp{fo}. Still trivial. To do something more powerful, you |
| 266 | need to use one of the special regular expression constructs. |
| 267 | |
| 268 | @menu |
| 269 | * Regexp Special:: Special characters in regular expressions. |
| 270 | * Char Classes:: Character classes used in regular expressions. |
| 271 | * Regexp Backslash:: Backslash-sequences in regular expressions. |
| 272 | @end menu |
| 273 | |
| 274 | @node Regexp Special |
| 275 | @subsubsection Special Characters in Regular Expressions |
| 276 | |
| 277 | Here is a list of the characters that are special in a regular |
| 278 | expression. |
| 279 | |
| 280 | @need 800 |
| 281 | @table @asis |
| 282 | @item @samp{.}@: @r{(Period)} |
| 283 | @cindex @samp{.} in regexp |
| 284 | is a special character that matches any single character except a newline. |
| 285 | Using concatenation, we can make regular expressions like @samp{a.b}, which |
| 286 | matches any three-character string that begins with @samp{a} and ends with |
| 287 | @samp{b}.@refill |
| 288 | |
| 289 | @item @samp{*} |
| 290 | @cindex @samp{*} in regexp |
| 291 | is not a construct by itself; it is a postfix operator that means to |
| 292 | match the preceding regular expression repetitively as many times as |
| 293 | possible. Thus, @samp{o*} matches any number of @samp{o}s (including no |
| 294 | @samp{o}s). |
| 295 | |
| 296 | @samp{*} always applies to the @emph{smallest} possible preceding |
| 297 | expression. Thus, @samp{fo*} has a repeating @samp{o}, not a repeating |
| 298 | @samp{fo}. It matches @samp{f}, @samp{fo}, @samp{foo}, and so on. |
| 299 | |
| 300 | The matcher processes a @samp{*} construct by matching, immediately, as |
| 301 | many repetitions as can be found. Then it continues with the rest of |
| 302 | the pattern. If that fails, backtracking occurs, discarding some of the |
| 303 | matches of the @samp{*}-modified construct in the hope that that will |
| 304 | make it possible to match the rest of the pattern. For example, in |
| 305 | matching @samp{ca*ar} against the string @samp{caaar}, the @samp{a*} |
| 306 | first tries to match all three @samp{a}s; but the rest of the pattern is |
| 307 | @samp{ar} and there is only @samp{r} left to match, so this try fails. |
| 308 | The next alternative is for @samp{a*} to match only two @samp{a}s. With |
| 309 | this choice, the rest of the regexp matches successfully. |
| 310 | |
| 311 | @strong{Warning:} Nested repetition operators take a long time, |
| 312 | or even forever, if they |
| 313 | lead to ambiguous matching. For example, trying to match the regular |
| 314 | expression @samp{\(x+y*\)*a} against the string |
| 315 | @samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz} could take hours before it |
| 316 | ultimately fails. Emacs must try each way of grouping the 35 |
| 317 | @samp{x}s before concluding that none of them can work. Even worse, |
| 318 | @samp{\(x*\)*} can match the null string in infinitely many ways, so |
| 319 | it causes an infinite loop. To avoid these problems, check nested |
| 320 | repetitions carefully, to make sure that they do not cause combinatorial |
| 321 | explosions in backtracking. |
| 322 | |
| 323 | @item @samp{+} |
| 324 | @cindex @samp{+} in regexp |
| 325 | is a postfix operator, similar to @samp{*} except that it must match |
| 326 | the preceding expression at least once. So, for example, @samp{ca+r} |
| 327 | matches the strings @samp{car} and @samp{caaaar} but not the string |
| 328 | @samp{cr}, whereas @samp{ca*r} matches all three strings. |
| 329 | |
| 330 | @item @samp{?} |
| 331 | @cindex @samp{?} in regexp |
| 332 | is a postfix operator, similar to @samp{*} except that it must match the |
| 333 | preceding expression either once or not at all. For example, |
| 334 | @samp{ca?r} matches @samp{car} or @samp{cr}; nothing else. |
| 335 | |
| 336 | @item @samp{*?}, @samp{+?}, @samp{??} |
| 337 | These are ``non-greedy'' variants of the operators @samp{*}, @samp{+} |
| 338 | and @samp{?}. Where those operators match the largest possible |
| 339 | substring (consistent with matching the entire containing expression), |
| 340 | the non-greedy variants match the smallest possible substring |
| 341 | (consistent with matching the entire containing expression). |
| 342 | |
| 343 | For example, the regular expression @samp{c[ad]*a} when applied to the |
| 344 | string @samp{cdaaada} matches the whole string; but the regular |
| 345 | expression @samp{c[ad]*?a}, applied to that same string, matches just |
| 346 | @samp{cda}. (The smallest possible match here for @samp{[ad]*?} that |
| 347 | permits the whole expression to match is @samp{d}.) |
| 348 | |
| 349 | @item @samp{[ @dots{} ]} |
| 350 | @cindex character alternative (in regexp) |
| 351 | @cindex @samp{[} in regexp |
| 352 | @cindex @samp{]} in regexp |
| 353 | is a @dfn{character alternative}, which begins with @samp{[} and is |
| 354 | terminated by @samp{]}. In the simplest case, the characters between |
| 355 | the two brackets are what this character alternative can match. |
| 356 | |
| 357 | Thus, @samp{[ad]} matches either one @samp{a} or one @samp{d}, and |
| 358 | @samp{[ad]*} matches any string composed of just @samp{a}s and @samp{d}s |
| 359 | (including the empty string), from which it follows that @samp{c[ad]*r} |
| 360 | matches @samp{cr}, @samp{car}, @samp{cdr}, @samp{caddaar}, etc. |
| 361 | |
| 362 | You can also include character ranges in a character alternative, by |
| 363 | writing the starting and ending characters with a @samp{-} between them. |
| 364 | Thus, @samp{[a-z]} matches any lower-case @acronym{ASCII} letter. |
| 365 | Ranges may be intermixed freely with individual characters, as in |
| 366 | @samp{[a-z$%.]}, which matches any lower case @acronym{ASCII} letter |
| 367 | or @samp{$}, @samp{%} or period. |
| 368 | |
| 369 | Note that the usual regexp special characters are not special inside a |
| 370 | character alternative. A completely different set of characters is |
| 371 | special inside character alternatives: @samp{]}, @samp{-} and @samp{^}. |
| 372 | |
| 373 | To include a @samp{]} in a character alternative, you must make it the |
| 374 | first character. For example, @samp{[]a]} matches @samp{]} or @samp{a}. |
| 375 | To include a @samp{-}, write @samp{-} as the first or last character of |
| 376 | the character alternative, or put it after a range. Thus, @samp{[]-]} |
| 377 | matches both @samp{]} and @samp{-}. |
| 378 | |
| 379 | To include @samp{^} in a character alternative, put it anywhere but at |
| 380 | the beginning. |
| 381 | |
| 382 | The beginning and end of a range of multibyte characters must be in |
| 383 | the same character set (@pxref{Character Sets}). Thus, |
| 384 | @code{"[\x8e0-\x97c]"} is invalid because character 0x8e0 (@samp{a} |
| 385 | with grave accent) is in the Emacs character set for Latin-1 but the |
| 386 | character 0x97c (@samp{u} with diaeresis) is in the Emacs character |
| 387 | set for Latin-2. (We use Lisp string syntax to write that example, |
| 388 | and a few others in the next few paragraphs, in order to include hex |
| 389 | escape sequences in them.) |
| 390 | |
| 391 | If a range starts with a unibyte character @var{c} and ends with a |
| 392 | multibyte character @var{c2}, the range is divided into two parts: one |
| 393 | is @samp{@var{c}..?\377}, the other is @samp{@var{c1}..@var{c2}}, where |
| 394 | @var{c1} is the first character of the charset to which @var{c2} |
| 395 | belongs. |
| 396 | |
| 397 | You cannot always match all non-@acronym{ASCII} characters with the regular |
| 398 | expression @code{"[\200-\377]"}. This works when searching a unibyte |
| 399 | buffer or string (@pxref{Text Representations}), but not in a multibyte |
| 400 | buffer or string, because many non-@acronym{ASCII} characters have codes |
| 401 | above octal 0377. However, the regular expression @code{"[^\000-\177]"} |
| 402 | does match all non-@acronym{ASCII} characters (see below regarding @samp{^}), |
| 403 | in both multibyte and unibyte representations, because only the |
| 404 | @acronym{ASCII} characters are excluded. |
| 405 | |
| 406 | A character alternative can also specify named |
| 407 | character classes (@pxref{Char Classes}). This is a POSIX feature whose |
| 408 | syntax is @samp{[:@var{class}:]}. Using a character class is equivalent |
| 409 | to mentioning each of the characters in that class; but the latter is |
| 410 | not feasible in practice, since some classes include thousands of |
| 411 | different characters. |
| 412 | |
| 413 | @item @samp{[^ @dots{} ]} |
| 414 | @cindex @samp{^} in regexp |
| 415 | @samp{[^} begins a @dfn{complemented character alternative}. This |
| 416 | matches any character except the ones specified. Thus, |
| 417 | @samp{[^a-z0-9A-Z]} matches all characters @emph{except} letters and |
| 418 | digits. |
| 419 | |
| 420 | @samp{^} is not special in a character alternative unless it is the first |
| 421 | character. The character following the @samp{^} is treated as if it |
| 422 | were first (in other words, @samp{-} and @samp{]} are not special there). |
| 423 | |
| 424 | A complemented character alternative can match a newline, unless newline is |
| 425 | mentioned as one of the characters not to match. This is in contrast to |
| 426 | the handling of regexps in programs such as @code{grep}. |
| 427 | |
| 428 | @item @samp{^} |
| 429 | @cindex beginning of line in regexp |
| 430 | When matching a buffer, @samp{^} matches the empty string, but only at the |
| 431 | beginning of a line in the text being matched (or the beginning of the |
| 432 | accessible portion of the buffer). Otherwise it fails to match |
| 433 | anything. Thus, @samp{^foo} matches a @samp{foo} that occurs at the |
| 434 | beginning of a line. |
| 435 | |
| 436 | When matching a string instead of a buffer, @samp{^} matches at the |
| 437 | beginning of the string or after a newline character. |
| 438 | |
| 439 | For historical compatibility reasons, @samp{^} can be used only at the |
| 440 | beginning of the regular expression, or after @samp{\(} or @samp{\|}. |
| 441 | |
| 442 | @item @samp{$} |
| 443 | @cindex @samp{$} in regexp |
| 444 | @cindex end of line in regexp |
| 445 | is similar to @samp{^} but matches only at the end of a line (or the |
| 446 | end of the accessible portion of the buffer). Thus, @samp{x+$} |
| 447 | matches a string of one @samp{x} or more at the end of a line. |
| 448 | |
| 449 | When matching a string instead of a buffer, @samp{$} matches at the end |
| 450 | of the string or before a newline character. |
| 451 | |
| 452 | For historical compatibility reasons, @samp{$} can be used only at the |
| 453 | end of the regular expression, or before @samp{\)} or @samp{\|}. |
| 454 | |
| 455 | @item @samp{\} |
| 456 | @cindex @samp{\} in regexp |
| 457 | has two functions: it quotes the special characters (including |
| 458 | @samp{\}), and it introduces additional special constructs. |
| 459 | |
| 460 | Because @samp{\} quotes special characters, @samp{\$} is a regular |
| 461 | expression that matches only @samp{$}, and @samp{\[} is a regular |
| 462 | expression that matches only @samp{[}, and so on. |
| 463 | |
| 464 | Note that @samp{\} also has special meaning in the read syntax of Lisp |
| 465 | strings (@pxref{String Type}), and must be quoted with @samp{\}. For |
| 466 | example, the regular expression that matches the @samp{\} character is |
| 467 | @samp{\\}. To write a Lisp string that contains the characters |
| 468 | @samp{\\}, Lisp syntax requires you to quote each @samp{\} with another |
| 469 | @samp{\}. Therefore, the read syntax for a regular expression matching |
| 470 | @samp{\} is @code{"\\\\"}.@refill |
| 471 | @end table |
| 472 | |
| 473 | @strong{Please note:} For historical compatibility, special characters |
| 474 | are treated as ordinary ones if they are in contexts where their special |
| 475 | meanings make no sense. For example, @samp{*foo} treats @samp{*} as |
| 476 | ordinary since there is no preceding expression on which the @samp{*} |
| 477 | can act. It is poor practice to depend on this behavior; quote the |
| 478 | special character anyway, regardless of where it appears.@refill |
| 479 | |
| 480 | As a @samp{\} is not special inside a character alternative, it can |
| 481 | never remove the special meaning of @samp{-} or @samp{]}. So you |
| 482 | should not quote these characters when they have no special meaning |
| 483 | either. This would not clarify anything, since backslashes can |
| 484 | legitimately precede these characters where they @emph{have} special |
| 485 | meaning, as in @samp{[^\]} (@code{"[^\\]"} for Lisp string syntax), |
| 486 | which matches any single character except a backslash. |
| 487 | |
| 488 | In practice, most @samp{]} that occur in regular expressions close a |
| 489 | character alternative and hence are special. However, occasionally a |
| 490 | regular expression may try to match a complex pattern of literal |
| 491 | @samp{[} and @samp{]}. In such situations, it sometimes may be |
| 492 | necessary to carefully parse the regexp from the start to determine |
| 493 | which square brackets enclose a character alternative. For example, |
| 494 | @samp{[^][]]} consists of the complemented character alternative |
| 495 | @samp{[^][]} (which matches any single character that is not a square |
| 496 | bracket), followed by a literal @samp{]}. |
| 497 | |
| 498 | The exact rules are that at the beginning of a regexp, @samp{[} is |
| 499 | special and @samp{]} not. This lasts until the first unquoted |
| 500 | @samp{[}, after which we are in a character alternative; @samp{[} is |
| 501 | no longer special (except when it starts a character class) but @samp{]} |
| 502 | is special, unless it immediately follows the special @samp{[} or that |
| 503 | @samp{[} followed by a @samp{^}. This lasts until the next special |
| 504 | @samp{]} that does not end a character class. This ends the character |
| 505 | alternative and restores the ordinary syntax of regular expressions; |
| 506 | an unquoted @samp{[} is special again and a @samp{]} not. |
| 507 | |
| 508 | @node Char Classes |
| 509 | @subsubsection Character Classes |
| 510 | @cindex character classes in regexp |
| 511 | |
| 512 | Here is a table of the classes you can use in a character alternative, |
| 513 | and what they mean: |
| 514 | |
| 515 | @table @samp |
| 516 | @item [:ascii:] |
| 517 | This matches any @acronym{ASCII} (unibyte) character. |
| 518 | @item [:alnum:] |
| 519 | This matches any letter or digit. (At present, for multibyte |
| 520 | characters, it matches anything that has word syntax.) |
| 521 | @item [:alpha:] |
| 522 | This matches any letter. (At present, for multibyte characters, it |
| 523 | matches anything that has word syntax.) |
| 524 | @item [:blank:] |
| 525 | This matches space and tab only. |
| 526 | @item [:cntrl:] |
| 527 | This matches any @acronym{ASCII} control character. |
| 528 | @item [:digit:] |
| 529 | This matches @samp{0} through @samp{9}. Thus, @samp{[-+[:digit:]]} |
| 530 | matches any digit, as well as @samp{+} and @samp{-}. |
| 531 | @item [:graph:] |
| 532 | This matches graphic characters---everything except @acronym{ASCII} control |
| 533 | characters, space, and the delete character. |
| 534 | @item [:lower:] |
| 535 | This matches any lower-case letter, as determined by |
| 536 | the current case table (@pxref{Case Tables}). |
| 537 | @item [:nonascii:] |
| 538 | This matches any non-@acronym{ASCII} (multibyte) character. |
| 539 | @item [:print:] |
| 540 | This matches printing characters---everything except @acronym{ASCII} control |
| 541 | characters and the delete character. |
| 542 | @item [:punct:] |
| 543 | This matches any punctuation character. (At present, for multibyte |
| 544 | characters, it matches anything that has non-word syntax.) |
| 545 | @item [:space:] |
| 546 | This matches any character that has whitespace syntax |
| 547 | (@pxref{Syntax Class Table}). |
| 548 | @item [:upper:] |
| 549 | This matches any upper-case letter, as determined by |
| 550 | the current case table (@pxref{Case Tables}). |
| 551 | @item [:word:] |
| 552 | This matches any character that has word syntax (@pxref{Syntax Class |
| 553 | Table}). |
| 554 | @item [:xdigit:] |
| 555 | This matches the hexadecimal digits: @samp{0} through @samp{9}, @samp{a} |
| 556 | through @samp{f} and @samp{A} through @samp{F}. |
| 557 | @end table |
| 558 | |
| 559 | @node Regexp Backslash |
| 560 | @subsubsection Backslash Constructs in Regular Expressions |
| 561 | |
| 562 | For the most part, @samp{\} followed by any character matches only |
| 563 | that character. However, there are several exceptions: certain |
| 564 | two-character sequences starting with @samp{\} that have special |
| 565 | meanings. (The character after the @samp{\} in such a sequence is |
| 566 | always ordinary when used on its own.) Here is a table of the special |
| 567 | @samp{\} constructs. |
| 568 | |
| 569 | @table @samp |
| 570 | @item \| |
| 571 | @cindex @samp{|} in regexp |
| 572 | @cindex regexp alternative |
| 573 | specifies an alternative. |
| 574 | Two regular expressions @var{a} and @var{b} with @samp{\|} in |
| 575 | between form an expression that matches anything that either @var{a} or |
| 576 | @var{b} matches.@refill |
| 577 | |
| 578 | Thus, @samp{foo\|bar} matches either @samp{foo} or @samp{bar} |
| 579 | but no other string.@refill |
| 580 | |
| 581 | @samp{\|} applies to the largest possible surrounding expressions. Only a |
| 582 | surrounding @samp{\( @dots{} \)} grouping can limit the grouping power of |
| 583 | @samp{\|}.@refill |
| 584 | |
| 585 | If you need full backtracking capability to handle multiple uses of |
| 586 | @samp{\|}, use the POSIX regular expression functions (@pxref{POSIX |
| 587 | Regexps}). |
| 588 | |
| 589 | @item \@{@var{m}\@} |
| 590 | is a postfix operator that repeats the previous pattern exactly @var{m} |
| 591 | times. Thus, @samp{x\@{5\@}} matches the string @samp{xxxxx} |
| 592 | and nothing else. @samp{c[ad]\@{3\@}r} matches string such as |
| 593 | @samp{caaar}, @samp{cdddr}, @samp{cadar}, and so on. |
| 594 | |
| 595 | @item \@{@var{m},@var{n}\@} |
| 596 | is a more general postfix operator that specifies repetition with a |
| 597 | minimum of @var{m} repeats and a maximum of @var{n} repeats. If @var{m} |
| 598 | is omitted, the minimum is 0; if @var{n} is omitted, there is no |
| 599 | maximum. |
| 600 | |
| 601 | For example, @samp{c[ad]\@{1,2\@}r} matches the strings @samp{car}, |
| 602 | @samp{cdr}, @samp{caar}, @samp{cadr}, @samp{cdar}, and @samp{cddr}, and |
| 603 | nothing else.@* |
| 604 | @samp{\@{0,1\@}} or @samp{\@{,1\@}} is equivalent to @samp{?}. @* |
| 605 | @samp{\@{0,\@}} or @samp{\@{,\@}} is equivalent to @samp{*}. @* |
| 606 | @samp{\@{1,\@}} is equivalent to @samp{+}. |
| 607 | |
| 608 | @item \( @dots{} \) |
| 609 | @cindex @samp{(} in regexp |
| 610 | @cindex @samp{)} in regexp |
| 611 | @cindex regexp grouping |
| 612 | is a grouping construct that serves three purposes: |
| 613 | |
| 614 | @enumerate |
| 615 | @item |
| 616 | To enclose a set of @samp{\|} alternatives for other operations. Thus, |
| 617 | the regular expression @samp{\(foo\|bar\)x} matches either @samp{foox} |
| 618 | or @samp{barx}. |
| 619 | |
| 620 | @item |
| 621 | To enclose a complicated expression for the postfix operators @samp{*}, |
| 622 | @samp{+} and @samp{?} to operate on. Thus, @samp{ba\(na\)*} matches |
| 623 | @samp{ba}, @samp{bana}, @samp{banana}, @samp{bananana}, etc., with any |
| 624 | number (zero or more) of @samp{na} strings. |
| 625 | |
| 626 | @item |
| 627 | To record a matched substring for future reference with |
| 628 | @samp{\@var{digit}} (see below). |
| 629 | @end enumerate |
| 630 | |
| 631 | This last application is not a consequence of the idea of a |
| 632 | parenthetical grouping; it is a separate feature that was assigned as a |
| 633 | second meaning to the same @samp{\( @dots{} \)} construct because, in |
| 634 | practice, there was usually no conflict between the two meanings. But |
| 635 | occasionally there is a conflict, and that led to the introduction of |
| 636 | shy groups. |
| 637 | |
| 638 | @item \(?: @dots{} \) |
| 639 | is the @dfn{shy group} construct. A shy group serves the first two |
| 640 | purposes of an ordinary group (controlling the nesting of other |
| 641 | operators), but it does not get a number, so you cannot refer back to |
| 642 | its value with @samp{\@var{digit}}. |
| 643 | |
| 644 | Shy groups are particularly useful for mechanically-constructed regular |
| 645 | expressions because they can be added automatically without altering the |
| 646 | numbering of any ordinary, non-shy groups. |
| 647 | |
| 648 | @item \@var{digit} |
| 649 | matches the same text that matched the @var{digit}th occurrence of a |
| 650 | grouping (@samp{\( @dots{} \)}) construct. |
| 651 | |
| 652 | In other words, after the end of a group, the matcher remembers the |
| 653 | beginning and end of the text matched by that group. Later on in the |
| 654 | regular expression you can use @samp{\} followed by @var{digit} to |
| 655 | match that same text, whatever it may have been. |
| 656 | |
| 657 | The strings matching the first nine grouping constructs appearing in |
| 658 | the entire regular expression passed to a search or matching function |
| 659 | are assigned numbers 1 through 9 in the order that the open |
| 660 | parentheses appear in the regular expression. So you can use |
| 661 | @samp{\1} through @samp{\9} to refer to the text matched by the |
| 662 | corresponding grouping constructs. |
| 663 | |
| 664 | For example, @samp{\(.*\)\1} matches any newline-free string that is |
| 665 | composed of two identical halves. The @samp{\(.*\)} matches the first |
| 666 | half, which may be anything, but the @samp{\1} that follows must match |
| 667 | the same exact text. |
| 668 | |
| 669 | If a @samp{\( @dots{} \)} construct matches more than once (which can |
| 670 | happen, for instance, if it is followed by @samp{*}), only the last |
| 671 | match is recorded. |
| 672 | |
| 673 | If a particular grouping construct in the regular expression was never |
| 674 | matched---for instance, if it appears inside of an alternative that |
| 675 | wasn't used, or inside of a repetition that repeated zero times---then |
| 676 | the corresponding @samp{\@var{digit}} construct never matches |
| 677 | anything. To use an artificial example,, @samp{\(foo\(b*\)\|lose\)\2} |
| 678 | cannot match @samp{lose}: the second alternative inside the larger |
| 679 | group matches it, but then @samp{\2} is undefined and can't match |
| 680 | anything. But it can match @samp{foobb}, because the first |
| 681 | alternative matches @samp{foob} and @samp{\2} matches @samp{b}. |
| 682 | |
| 683 | @item \w |
| 684 | @cindex @samp{\w} in regexp |
| 685 | matches any word-constituent character. The editor syntax table |
| 686 | determines which characters these are. @xref{Syntax Tables}. |
| 687 | |
| 688 | @item \W |
| 689 | @cindex @samp{\W} in regexp |
| 690 | matches any character that is not a word constituent. |
| 691 | |
| 692 | @item \s@var{code} |
| 693 | @cindex @samp{\s} in regexp |
| 694 | matches any character whose syntax is @var{code}. Here @var{code} is a |
| 695 | character that represents a syntax code: thus, @samp{w} for word |
| 696 | constituent, @samp{-} for whitespace, @samp{(} for open parenthesis, |
| 697 | etc. To represent whitespace syntax, use either @samp{-} or a space |
| 698 | character. @xref{Syntax Class Table}, for a list of syntax codes and |
| 699 | the characters that stand for them. |
| 700 | |
| 701 | @item \S@var{code} |
| 702 | @cindex @samp{\S} in regexp |
| 703 | matches any character whose syntax is not @var{code}. |
| 704 | |
| 705 | @item \c@var{c} |
| 706 | matches any character whose category is @var{c}. Here @var{c} is a |
| 707 | character that represents a category: thus, @samp{c} for Chinese |
| 708 | characters or @samp{g} for Greek characters in the standard category |
| 709 | table. |
| 710 | |
| 711 | @item \C@var{c} |
| 712 | matches any character whose category is not @var{c}. |
| 713 | @end table |
| 714 | |
| 715 | The following regular expression constructs match the empty string---that is, |
| 716 | they don't use up any characters---but whether they match depends on the |
| 717 | context. For all, the beginning and end of the accessible portion of |
| 718 | the buffer are treated as if they were the actual beginning and end of |
| 719 | the buffer. |
| 720 | |
| 721 | @table @samp |
| 722 | @item \` |
| 723 | @cindex @samp{\`} in regexp |
| 724 | matches the empty string, but only at the beginning |
| 725 | of the buffer or string being matched against. |
| 726 | |
| 727 | @item \' |
| 728 | @cindex @samp{\'} in regexp |
| 729 | matches the empty string, but only at the end of |
| 730 | the buffer or string being matched against. |
| 731 | |
| 732 | @item \= |
| 733 | @cindex @samp{\=} in regexp |
| 734 | matches the empty string, but only at point. |
| 735 | (This construct is not defined when matching against a string.) |
| 736 | |
| 737 | @item \b |
| 738 | @cindex @samp{\b} in regexp |
| 739 | matches the empty string, but only at the beginning or |
| 740 | end of a word. Thus, @samp{\bfoo\b} matches any occurrence of |
| 741 | @samp{foo} as a separate word. @samp{\bballs?\b} matches |
| 742 | @samp{ball} or @samp{balls} as a separate word.@refill |
| 743 | |
| 744 | @samp{\b} matches at the beginning or end of the buffer (or string) |
| 745 | regardless of what text appears next to it. |
| 746 | |
| 747 | @item \B |
| 748 | @cindex @samp{\B} in regexp |
| 749 | matches the empty string, but @emph{not} at the beginning or |
| 750 | end of a word, nor at the beginning or end of the buffer (or string). |
| 751 | |
| 752 | @item \< |
| 753 | @cindex @samp{\<} in regexp |
| 754 | matches the empty string, but only at the beginning of a word. |
| 755 | @samp{\<} matches at the beginning of the buffer (or string) only if a |
| 756 | word-constituent character follows. |
| 757 | |
| 758 | @item \> |
| 759 | @cindex @samp{\>} in regexp |
| 760 | matches the empty string, but only at the end of a word. @samp{\>} |
| 761 | matches at the end of the buffer (or string) only if the contents end |
| 762 | with a word-constituent character. |
| 763 | |
| 764 | @item \_< |
| 765 | @cindex @samp{\_<} in regexp |
| 766 | matches the empty string, but only at the beginning of a symbol. A |
| 767 | symbol is a sequence of one or more word or symbol constituent |
| 768 | characters. @samp{\_<} matches at the beginning of the buffer (or |
| 769 | string) only if a symbol-constituent character follows. |
| 770 | |
| 771 | @item \_> |
| 772 | @cindex @samp{\_>} in regexp |
| 773 | matches the empty string, but only at the end of a symbol. @samp{\_>} |
| 774 | matches at the end of the buffer (or string) only if the contents end |
| 775 | with a symbol-constituent character. |
| 776 | @end table |
| 777 | |
| 778 | @kindex invalid-regexp |
| 779 | Not every string is a valid regular expression. For example, a string |
| 780 | that ends inside a character alternative without terminating @samp{]} |
| 781 | is invalid, and so is a string that ends with a single @samp{\}. If |
| 782 | an invalid regular expression is passed to any of the search functions, |
| 783 | an @code{invalid-regexp} error is signaled. |
| 784 | |
| 785 | @node Regexp Example |
| 786 | @comment node-name, next, previous, up |
| 787 | @subsection Complex Regexp Example |
| 788 | |
| 789 | Here is a complicated regexp which was formerly used by Emacs to |
| 790 | recognize the end of a sentence together with any whitespace that |
| 791 | follows. (Nowadays Emacs uses a similar but more complex default |
| 792 | regexp constructed by the function @code{sentence-end}. |
| 793 | @xref{Standard Regexps}.) |
| 794 | |
| 795 | First, we show the regexp as a string in Lisp syntax to distinguish |
| 796 | spaces from tab characters. The string constant begins and ends with a |
| 797 | double-quote. @samp{\"} stands for a double-quote as part of the |
| 798 | string, @samp{\\} for a backslash as part of the string, @samp{\t} for a |
| 799 | tab and @samp{\n} for a newline. |
| 800 | |
| 801 | @example |
| 802 | "[.?!][]\"')@}]*\\($\\| $\\|\t\\|@ @ \\)[ \t\n]*" |
| 803 | @end example |
| 804 | |
| 805 | @noindent |
| 806 | In contrast, if you evaluate this string, you will see the following: |
| 807 | |
| 808 | @example |
| 809 | @group |
| 810 | "[.?!][]\"')@}]*\\($\\| $\\|\t\\|@ @ \\)[ \t\n]*" |
| 811 | @result{} "[.?!][]\"')@}]*\\($\\| $\\| \\|@ @ \\)[ |
| 812 | ]*" |
| 813 | @end group |
| 814 | @end example |
| 815 | |
| 816 | @noindent |
| 817 | In this output, tab and newline appear as themselves. |
| 818 | |
| 819 | This regular expression contains four parts in succession and can be |
| 820 | deciphered as follows: |
| 821 | |
| 822 | @table @code |
| 823 | @item [.?!] |
| 824 | The first part of the pattern is a character alternative that matches |
| 825 | any one of three characters: period, question mark, and exclamation |
| 826 | mark. The match must begin with one of these three characters. (This |
| 827 | is one point where the new default regexp used by Emacs differs from |
| 828 | the old. The new value also allows some non-@acronym{ASCII} |
| 829 | characters that end a sentence without any following whitespace.) |
| 830 | |
| 831 | @item []\"')@}]* |
| 832 | The second part of the pattern matches any closing braces and quotation |
| 833 | marks, zero or more of them, that may follow the period, question mark |
| 834 | or exclamation mark. The @code{\"} is Lisp syntax for a double-quote in |
| 835 | a string. The @samp{*} at the end indicates that the immediately |
| 836 | preceding regular expression (a character alternative, in this case) may be |
| 837 | repeated zero or more times. |
| 838 | |
| 839 | @item \\($\\|@ $\\|\t\\|@ @ \\) |
| 840 | The third part of the pattern matches the whitespace that follows the |
| 841 | end of a sentence: the end of a line (optionally with a space), or a |
| 842 | tab, or two spaces. The double backslashes mark the parentheses and |
| 843 | vertical bars as regular expression syntax; the parentheses delimit a |
| 844 | group and the vertical bars separate alternatives. The dollar sign is |
| 845 | used to match the end of a line. |
| 846 | |
| 847 | @item [ \t\n]* |
| 848 | Finally, the last part of the pattern matches any additional whitespace |
| 849 | beyond the minimum needed to end a sentence. |
| 850 | @end table |
| 851 | |
| 852 | @node Regexp Functions |
| 853 | @subsection Regular Expression Functions |
| 854 | |
| 855 | These functions operate on regular expressions. |
| 856 | |
| 857 | @defun regexp-quote string |
| 858 | This function returns a regular expression whose only exact match is |
| 859 | @var{string}. Using this regular expression in @code{looking-at} will |
| 860 | succeed only if the next characters in the buffer are @var{string}; |
| 861 | using it in a search function will succeed if the text being searched |
| 862 | contains @var{string}. |
| 863 | |
| 864 | This allows you to request an exact string match or search when calling |
| 865 | a function that wants a regular expression. |
| 866 | |
| 867 | @example |
| 868 | @group |
| 869 | (regexp-quote "^The cat$") |
| 870 | @result{} "\\^The cat\\$" |
| 871 | @end group |
| 872 | @end example |
| 873 | |
| 874 | One use of @code{regexp-quote} is to combine an exact string match with |
| 875 | context described as a regular expression. For example, this searches |
| 876 | for the string that is the value of @var{string}, surrounded by |
| 877 | whitespace: |
| 878 | |
| 879 | @example |
| 880 | @group |
| 881 | (re-search-forward |
| 882 | (concat "\\s-" (regexp-quote string) "\\s-")) |
| 883 | @end group |
| 884 | @end example |
| 885 | @end defun |
| 886 | |
| 887 | @defun regexp-opt strings &optional paren |
| 888 | This function returns an efficient regular expression that will match |
| 889 | any of the strings in the list @var{strings}. This is useful when you |
| 890 | need to make matching or searching as fast as possible---for example, |
| 891 | for Font Lock mode. |
| 892 | |
| 893 | If the optional argument @var{paren} is non-@code{nil}, then the |
| 894 | returned regular expression is always enclosed by at least one |
| 895 | parentheses-grouping construct. If @var{paren} is @code{words}, then |
| 896 | that construct is additionally surrounded by @samp{\<} and @samp{\>}. |
| 897 | |
| 898 | This simplified definition of @code{regexp-opt} produces a |
| 899 | regular expression which is equivalent to the actual value |
| 900 | (but not as efficient): |
| 901 | |
| 902 | @example |
| 903 | (defun regexp-opt (strings paren) |
| 904 | (let ((open-paren (if paren "\\(" "")) |
| 905 | (close-paren (if paren "\\)" ""))) |
| 906 | (concat open-paren |
| 907 | (mapconcat 'regexp-quote strings "\\|") |
| 908 | close-paren))) |
| 909 | @end example |
| 910 | @end defun |
| 911 | |
| 912 | @defun regexp-opt-depth regexp |
| 913 | This function returns the total number of grouping constructs |
| 914 | (parenthesized expressions) in @var{regexp}. (This does not include |
| 915 | shy groups.) |
| 916 | @end defun |
| 917 | |
| 918 | @node Regexp Search |
| 919 | @section Regular Expression Searching |
| 920 | @cindex regular expression searching |
| 921 | @cindex regexp searching |
| 922 | @cindex searching for regexp |
| 923 | |
| 924 | In GNU Emacs, you can search for the next match for a regular |
| 925 | expression either incrementally or not. For incremental search |
| 926 | commands, see @ref{Regexp Search, , Regular Expression Search, emacs, |
| 927 | The GNU Emacs Manual}. Here we describe only the search functions |
| 928 | useful in programs. The principal one is @code{re-search-forward}. |
| 929 | |
| 930 | These search functions convert the regular expression to multibyte if |
| 931 | the buffer is multibyte; they convert the regular expression to unibyte |
| 932 | if the buffer is unibyte. @xref{Text Representations}. |
| 933 | |
| 934 | @deffn Command re-search-forward regexp &optional limit noerror repeat |
| 935 | This function searches forward in the current buffer for a string of |
| 936 | text that is matched by the regular expression @var{regexp}. The |
| 937 | function skips over any amount of text that is not matched by |
| 938 | @var{regexp}, and leaves point at the end of the first match found. |
| 939 | It returns the new value of point. |
| 940 | |
| 941 | If @var{limit} is non-@code{nil}, it must be a position in the current |
| 942 | buffer. It specifies the upper bound to the search. No match |
| 943 | extending after that position is accepted. |
| 944 | |
| 945 | If @var{repeat} is supplied, it must be a positive number; the search |
| 946 | is repeated that many times; each repetition starts at the end of the |
| 947 | previous match. If all these successive searches succeed, the search |
| 948 | succeeds, moving point and returning its new value. Otherwise the |
| 949 | search fails. What @code{re-search-forward} does when the search |
| 950 | fails depends on the value of @var{noerror}: |
| 951 | |
| 952 | @table @asis |
| 953 | @item @code{nil} |
| 954 | Signal a @code{search-failed} error. |
| 955 | @item @code{t} |
| 956 | Do nothing and return @code{nil}. |
| 957 | @item anything else |
| 958 | Move point to @var{limit} (or the end of the accessible portion of the |
| 959 | buffer) and return @code{nil}. |
| 960 | @end table |
| 961 | |
| 962 | In the following example, point is initially before the @samp{T}. |
| 963 | Evaluating the search call moves point to the end of that line (between |
| 964 | the @samp{t} of @samp{hat} and the newline). |
| 965 | |
| 966 | @example |
| 967 | @group |
| 968 | ---------- Buffer: foo ---------- |
| 969 | I read "@point{}The cat in the hat |
| 970 | comes back" twice. |
| 971 | ---------- Buffer: foo ---------- |
| 972 | @end group |
| 973 | |
| 974 | @group |
| 975 | (re-search-forward "[a-z]+" nil t 5) |
| 976 | @result{} 27 |
| 977 | |
| 978 | ---------- Buffer: foo ---------- |
| 979 | I read "The cat in the hat@point{} |
| 980 | comes back" twice. |
| 981 | ---------- Buffer: foo ---------- |
| 982 | @end group |
| 983 | @end example |
| 984 | @end deffn |
| 985 | |
| 986 | @deffn Command re-search-backward regexp &optional limit noerror repeat |
| 987 | This function searches backward in the current buffer for a string of |
| 988 | text that is matched by the regular expression @var{regexp}, leaving |
| 989 | point at the beginning of the first text found. |
| 990 | |
| 991 | This function is analogous to @code{re-search-forward}, but they are not |
| 992 | simple mirror images. @code{re-search-forward} finds the match whose |
| 993 | beginning is as close as possible to the starting point. If |
| 994 | @code{re-search-backward} were a perfect mirror image, it would find the |
| 995 | match whose end is as close as possible. However, in fact it finds the |
| 996 | match whose beginning is as close as possible (and yet ends before the |
| 997 | starting point). The reason for this is that matching a regular |
| 998 | expression at a given spot always works from beginning to end, and |
| 999 | starts at a specified beginning position. |
| 1000 | |
| 1001 | A true mirror-image of @code{re-search-forward} would require a special |
| 1002 | feature for matching regular expressions from end to beginning. It's |
| 1003 | not worth the trouble of implementing that. |
| 1004 | @end deffn |
| 1005 | |
| 1006 | @defun string-match regexp string &optional start |
| 1007 | This function returns the index of the start of the first match for |
| 1008 | the regular expression @var{regexp} in @var{string}, or @code{nil} if |
| 1009 | there is no match. If @var{start} is non-@code{nil}, the search starts |
| 1010 | at that index in @var{string}. |
| 1011 | |
| 1012 | For example, |
| 1013 | |
| 1014 | @example |
| 1015 | @group |
| 1016 | (string-match |
| 1017 | "quick" "The quick brown fox jumped quickly.") |
| 1018 | @result{} 4 |
| 1019 | @end group |
| 1020 | @group |
| 1021 | (string-match |
| 1022 | "quick" "The quick brown fox jumped quickly." 8) |
| 1023 | @result{} 27 |
| 1024 | @end group |
| 1025 | @end example |
| 1026 | |
| 1027 | @noindent |
| 1028 | The index of the first character of the |
| 1029 | string is 0, the index of the second character is 1, and so on. |
| 1030 | |
| 1031 | After this function returns, the index of the first character beyond |
| 1032 | the match is available as @code{(match-end 0)}. @xref{Match Data}. |
| 1033 | |
| 1034 | @example |
| 1035 | @group |
| 1036 | (string-match |
| 1037 | "quick" "The quick brown fox jumped quickly." 8) |
| 1038 | @result{} 27 |
| 1039 | @end group |
| 1040 | |
| 1041 | @group |
| 1042 | (match-end 0) |
| 1043 | @result{} 32 |
| 1044 | @end group |
| 1045 | @end example |
| 1046 | @end defun |
| 1047 | |
| 1048 | @defun looking-at regexp |
| 1049 | This function determines whether the text in the current buffer directly |
| 1050 | following point matches the regular expression @var{regexp}. ``Directly |
| 1051 | following'' means precisely that: the search is ``anchored'' and it can |
| 1052 | succeed only starting with the first character following point. The |
| 1053 | result is @code{t} if so, @code{nil} otherwise. |
| 1054 | |
| 1055 | This function does not move point, but it updates the match data, which |
| 1056 | you can access using @code{match-beginning} and @code{match-end}. |
| 1057 | @xref{Match Data}. |
| 1058 | |
| 1059 | In this example, point is located directly before the @samp{T}. If it |
| 1060 | were anywhere else, the result would be @code{nil}. |
| 1061 | |
| 1062 | @example |
| 1063 | @group |
| 1064 | ---------- Buffer: foo ---------- |
| 1065 | I read "@point{}The cat in the hat |
| 1066 | comes back" twice. |
| 1067 | ---------- Buffer: foo ---------- |
| 1068 | |
| 1069 | (looking-at "The cat in the hat$") |
| 1070 | @result{} t |
| 1071 | @end group |
| 1072 | @end example |
| 1073 | @end defun |
| 1074 | |
| 1075 | @defun looking-back regexp &optional limit |
| 1076 | This function returns @code{t} if @var{regexp} matches text before |
| 1077 | point, ending at point, and @code{nil} otherwise. |
| 1078 | |
| 1079 | Because regular expression matching works only going forward, this is |
| 1080 | implemented by searching backwards from point for a match that ends at |
| 1081 | point. That can be quite slow if it has to search a long distance. |
| 1082 | You can bound the time required by specifying @var{limit}, which says |
| 1083 | not to search before @var{limit}. In this case, the match that is |
| 1084 | found must begin at or after @var{limit}. |
| 1085 | |
| 1086 | @example |
| 1087 | @group |
| 1088 | ---------- Buffer: foo ---------- |
| 1089 | I read "@point{}The cat in the hat |
| 1090 | comes back" twice. |
| 1091 | ---------- Buffer: foo ---------- |
| 1092 | |
| 1093 | (looking-back "read \"" 3) |
| 1094 | @result{} t |
| 1095 | (looking-back "read \"" 4) |
| 1096 | @result{} nil |
| 1097 | @end group |
| 1098 | @end example |
| 1099 | @end defun |
| 1100 | |
| 1101 | @defvar search-spaces-regexp |
| 1102 | If this variable is non-@code{nil}, it should be a regular expression |
| 1103 | that says how to search for whitespace. In that case, any group of |
| 1104 | spaces in a regular expression being searched for stands for use of |
| 1105 | this regular expression. However, spaces inside of constructs such as |
| 1106 | @samp{[@dots{}]} and @samp{*}, @samp{+}, @samp{?} are not affected by |
| 1107 | @code{search-spaces-regexp}. |
| 1108 | |
| 1109 | Since this variable affects all regular expression search and match |
| 1110 | constructs, you should bind it temporarily for as small as possible |
| 1111 | a part of the code. |
| 1112 | @end defvar |
| 1113 | |
| 1114 | @node POSIX Regexps |
| 1115 | @section POSIX Regular Expression Searching |
| 1116 | |
| 1117 | The usual regular expression functions do backtracking when necessary |
| 1118 | to handle the @samp{\|} and repetition constructs, but they continue |
| 1119 | this only until they find @emph{some} match. Then they succeed and |
| 1120 | report the first match found. |
| 1121 | |
| 1122 | This section describes alternative search functions which perform the |
| 1123 | full backtracking specified by the POSIX standard for regular expression |
| 1124 | matching. They continue backtracking until they have tried all |
| 1125 | possibilities and found all matches, so they can report the longest |
| 1126 | match, as required by POSIX. This is much slower, so use these |
| 1127 | functions only when you really need the longest match. |
| 1128 | |
| 1129 | The POSIX search and match functions do not properly support the |
| 1130 | non-greedy repetition operators. This is because POSIX backtracking |
| 1131 | conflicts with the semantics of non-greedy repetition. |
| 1132 | |
| 1133 | @defun posix-search-forward regexp &optional limit noerror repeat |
| 1134 | This is like @code{re-search-forward} except that it performs the full |
| 1135 | backtracking specified by the POSIX standard for regular expression |
| 1136 | matching. |
| 1137 | @end defun |
| 1138 | |
| 1139 | @defun posix-search-backward regexp &optional limit noerror repeat |
| 1140 | This is like @code{re-search-backward} except that it performs the full |
| 1141 | backtracking specified by the POSIX standard for regular expression |
| 1142 | matching. |
| 1143 | @end defun |
| 1144 | |
| 1145 | @defun posix-looking-at regexp |
| 1146 | This is like @code{looking-at} except that it performs the full |
| 1147 | backtracking specified by the POSIX standard for regular expression |
| 1148 | matching. |
| 1149 | @end defun |
| 1150 | |
| 1151 | @defun posix-string-match regexp string &optional start |
| 1152 | This is like @code{string-match} except that it performs the full |
| 1153 | backtracking specified by the POSIX standard for regular expression |
| 1154 | matching. |
| 1155 | @end defun |
| 1156 | |
| 1157 | @node Match Data |
| 1158 | @section The Match Data |
| 1159 | @cindex match data |
| 1160 | |
| 1161 | Emacs keeps track of the start and end positions of the segments of |
| 1162 | text found during a search; this is called the @dfn{match data}. |
| 1163 | Thanks to the match data, you can search for a complex pattern, such |
| 1164 | as a date in a mail message, and then extract parts of the match under |
| 1165 | control of the pattern. |
| 1166 | |
| 1167 | Because the match data normally describe the most recent search only, |
| 1168 | you must be careful not to do another search inadvertently between the |
| 1169 | search you wish to refer back to and the use of the match data. If you |
| 1170 | can't avoid another intervening search, you must save and restore the |
| 1171 | match data around it, to prevent it from being overwritten. |
| 1172 | |
| 1173 | @menu |
| 1174 | * Replacing Match:: Replacing a substring that was matched. |
| 1175 | * Simple Match Data:: Accessing single items of match data, |
| 1176 | such as where a particular subexpression started. |
| 1177 | * Entire Match Data:: Accessing the entire match data at once, as a list. |
| 1178 | * Saving Match Data:: Saving and restoring the match data. |
| 1179 | @end menu |
| 1180 | |
| 1181 | @node Replacing Match |
| 1182 | @subsection Replacing the Text that Matched |
| 1183 | |
| 1184 | This function replaces all or part of the text matched by the last |
| 1185 | search. It works by means of the match data. |
| 1186 | |
| 1187 | @cindex case in replacements |
| 1188 | @defun replace-match replacement &optional fixedcase literal string subexp |
| 1189 | This function replaces the text in the buffer (or in @var{string}) that |
| 1190 | was matched by the last search. It replaces that text with |
| 1191 | @var{replacement}. |
| 1192 | |
| 1193 | If you did the last search in a buffer, you should specify @code{nil} |
| 1194 | for @var{string} and make sure that the current buffer when you call |
| 1195 | @code{replace-match} is the one in which you did the searching or |
| 1196 | matching. Then @code{replace-match} does the replacement by editing |
| 1197 | the buffer; it leaves point at the end of the replacement text, and |
| 1198 | returns @code{t}. |
| 1199 | |
| 1200 | If you did the search in a string, pass the same string as @var{string}. |
| 1201 | Then @code{replace-match} does the replacement by constructing and |
| 1202 | returning a new string. |
| 1203 | |
| 1204 | If @var{fixedcase} is non-@code{nil}, then @code{replace-match} uses |
| 1205 | the replacement text without case conversion; otherwise, it converts |
| 1206 | the replacement text depending upon the capitalization of the text to |
| 1207 | be replaced. If the original text is all upper case, this converts |
| 1208 | the replacement text to upper case. If all words of the original text |
| 1209 | are capitalized, this capitalizes all the words of the replacement |
| 1210 | text. If all the words are one-letter and they are all upper case, |
| 1211 | they are treated as capitalized words rather than all-upper-case |
| 1212 | words. |
| 1213 | |
| 1214 | If @var{literal} is non-@code{nil}, then @var{replacement} is inserted |
| 1215 | exactly as it is, the only alterations being case changes as needed. |
| 1216 | If it is @code{nil} (the default), then the character @samp{\} is treated |
| 1217 | specially. If a @samp{\} appears in @var{replacement}, then it must be |
| 1218 | part of one of the following sequences: |
| 1219 | |
| 1220 | @table @asis |
| 1221 | @item @samp{\&} |
| 1222 | @cindex @samp{&} in replacement |
| 1223 | @samp{\&} stands for the entire text being replaced. |
| 1224 | |
| 1225 | @item @samp{\@var{n}} |
| 1226 | @cindex @samp{\@var{n}} in replacement |
| 1227 | @samp{\@var{n}}, where @var{n} is a digit, stands for the text that |
| 1228 | matched the @var{n}th subexpression in the original regexp. |
| 1229 | Subexpressions are those expressions grouped inside @samp{\(@dots{}\)}. |
| 1230 | If the @var{n}th subexpression never matched, an empty string is substituted. |
| 1231 | |
| 1232 | @item @samp{\\} |
| 1233 | @cindex @samp{\} in replacement |
| 1234 | @samp{\\} stands for a single @samp{\} in the replacement text. |
| 1235 | @end table |
| 1236 | |
| 1237 | These substitutions occur after case conversion, if any, |
| 1238 | so the strings they substitute are never case-converted. |
| 1239 | |
| 1240 | If @var{subexp} is non-@code{nil}, that says to replace just |
| 1241 | subexpression number @var{subexp} of the regexp that was matched, not |
| 1242 | the entire match. For example, after matching @samp{foo \(ba*r\)}, |
| 1243 | calling @code{replace-match} with 1 as @var{subexp} means to replace |
| 1244 | just the text that matched @samp{\(ba*r\)}. |
| 1245 | @end defun |
| 1246 | |
| 1247 | @node Simple Match Data |
| 1248 | @subsection Simple Match Data Access |
| 1249 | |
| 1250 | This section explains how to use the match data to find out what was |
| 1251 | matched by the last search or match operation, if it succeeded. |
| 1252 | |
| 1253 | You can ask about the entire matching text, or about a particular |
| 1254 | parenthetical subexpression of a regular expression. The @var{count} |
| 1255 | argument in the functions below specifies which. If @var{count} is |
| 1256 | zero, you are asking about the entire match. If @var{count} is |
| 1257 | positive, it specifies which subexpression you want. |
| 1258 | |
| 1259 | Recall that the subexpressions of a regular expression are those |
| 1260 | expressions grouped with escaped parentheses, @samp{\(@dots{}\)}. The |
| 1261 | @var{count}th subexpression is found by counting occurrences of |
| 1262 | @samp{\(} from the beginning of the whole regular expression. The first |
| 1263 | subexpression is numbered 1, the second 2, and so on. Only regular |
| 1264 | expressions can have subexpressions---after a simple string search, the |
| 1265 | only information available is about the entire match. |
| 1266 | |
| 1267 | Every successful search sets the match data. Therefore, you should |
| 1268 | query the match data immediately after searching, before calling any |
| 1269 | other function that might perform another search. Alternatively, you |
| 1270 | may save and restore the match data (@pxref{Saving Match Data}) around |
| 1271 | the call to functions that could perform another search. |
| 1272 | |
| 1273 | A search which fails may or may not alter the match data. In the |
| 1274 | past, a failing search did not do this, but we may change it in the |
| 1275 | future. So don't try to rely on the value of the match data after |
| 1276 | a failing search. |
| 1277 | |
| 1278 | @defun match-string count &optional in-string |
| 1279 | This function returns, as a string, the text matched in the last search |
| 1280 | or match operation. It returns the entire text if @var{count} is zero, |
| 1281 | or just the portion corresponding to the @var{count}th parenthetical |
| 1282 | subexpression, if @var{count} is positive. |
| 1283 | |
| 1284 | If the last such operation was done against a string with |
| 1285 | @code{string-match}, then you should pass the same string as the |
| 1286 | argument @var{in-string}. After a buffer search or match, |
| 1287 | you should omit @var{in-string} or pass @code{nil} for it; but you |
| 1288 | should make sure that the current buffer when you call |
| 1289 | @code{match-string} is the one in which you did the searching or |
| 1290 | matching. |
| 1291 | |
| 1292 | The value is @code{nil} if @var{count} is out of range, or for a |
| 1293 | subexpression inside a @samp{\|} alternative that wasn't used or a |
| 1294 | repetition that repeated zero times. |
| 1295 | @end defun |
| 1296 | |
| 1297 | @defun match-string-no-properties count &optional in-string |
| 1298 | This function is like @code{match-string} except that the result |
| 1299 | has no text properties. |
| 1300 | @end defun |
| 1301 | |
| 1302 | @defun match-beginning count |
| 1303 | This function returns the position of the start of text matched by the |
| 1304 | last regular expression searched for, or a subexpression of it. |
| 1305 | |
| 1306 | If @var{count} is zero, then the value is the position of the start of |
| 1307 | the entire match. Otherwise, @var{count} specifies a subexpression in |
| 1308 | the regular expression, and the value of the function is the starting |
| 1309 | position of the match for that subexpression. |
| 1310 | |
| 1311 | The value is @code{nil} for a subexpression inside a @samp{\|} |
| 1312 | alternative that wasn't used or a repetition that repeated zero times. |
| 1313 | @end defun |
| 1314 | |
| 1315 | @defun match-end count |
| 1316 | This function is like @code{match-beginning} except that it returns the |
| 1317 | position of the end of the match, rather than the position of the |
| 1318 | beginning. |
| 1319 | @end defun |
| 1320 | |
| 1321 | Here is an example of using the match data, with a comment showing the |
| 1322 | positions within the text: |
| 1323 | |
| 1324 | @example |
| 1325 | @group |
| 1326 | (string-match "\\(qu\\)\\(ick\\)" |
| 1327 | "The quick fox jumped quickly.") |
| 1328 | ;0123456789 |
| 1329 | @result{} 4 |
| 1330 | @end group |
| 1331 | |
| 1332 | @group |
| 1333 | (match-string 0 "The quick fox jumped quickly.") |
| 1334 | @result{} "quick" |
| 1335 | (match-string 1 "The quick fox jumped quickly.") |
| 1336 | @result{} "qu" |
| 1337 | (match-string 2 "The quick fox jumped quickly.") |
| 1338 | @result{} "ick" |
| 1339 | @end group |
| 1340 | |
| 1341 | @group |
| 1342 | (match-beginning 1) ; @r{The beginning of the match} |
| 1343 | @result{} 4 ; @r{with @samp{qu} is at index 4.} |
| 1344 | @end group |
| 1345 | |
| 1346 | @group |
| 1347 | (match-beginning 2) ; @r{The beginning of the match} |
| 1348 | @result{} 6 ; @r{with @samp{ick} is at index 6.} |
| 1349 | @end group |
| 1350 | |
| 1351 | @group |
| 1352 | (match-end 1) ; @r{The end of the match} |
| 1353 | @result{} 6 ; @r{with @samp{qu} is at index 6.} |
| 1354 | |
| 1355 | (match-end 2) ; @r{The end of the match} |
| 1356 | @result{} 9 ; @r{with @samp{ick} is at index 9.} |
| 1357 | @end group |
| 1358 | @end example |
| 1359 | |
| 1360 | Here is another example. Point is initially located at the beginning |
| 1361 | of the line. Searching moves point to between the space and the word |
| 1362 | @samp{in}. The beginning of the entire match is at the 9th character of |
| 1363 | the buffer (@samp{T}), and the beginning of the match for the first |
| 1364 | subexpression is at the 13th character (@samp{c}). |
| 1365 | |
| 1366 | @example |
| 1367 | @group |
| 1368 | (list |
| 1369 | (re-search-forward "The \\(cat \\)") |
| 1370 | (match-beginning 0) |
| 1371 | (match-beginning 1)) |
| 1372 | @result{} (9 9 13) |
| 1373 | @end group |
| 1374 | |
| 1375 | @group |
| 1376 | ---------- Buffer: foo ---------- |
| 1377 | I read "The cat @point{}in the hat comes back" twice. |
| 1378 | ^ ^ |
| 1379 | 9 13 |
| 1380 | ---------- Buffer: foo ---------- |
| 1381 | @end group |
| 1382 | @end example |
| 1383 | |
| 1384 | @noindent |
| 1385 | (In this case, the index returned is a buffer position; the first |
| 1386 | character of the buffer counts as 1.) |
| 1387 | |
| 1388 | @node Entire Match Data |
| 1389 | @subsection Accessing the Entire Match Data |
| 1390 | |
| 1391 | The functions @code{match-data} and @code{set-match-data} read or |
| 1392 | write the entire match data, all at once. |
| 1393 | |
| 1394 | @defun match-data &optional integers reuse reseat |
| 1395 | This function returns a list of positions (markers or integers) that |
| 1396 | record all the information on what text the last search matched. |
| 1397 | Element zero is the position of the beginning of the match for the |
| 1398 | whole expression; element one is the position of the end of the match |
| 1399 | for the expression. The next two elements are the positions of the |
| 1400 | beginning and end of the match for the first subexpression, and so on. |
| 1401 | In general, element |
| 1402 | @ifnottex |
| 1403 | number 2@var{n} |
| 1404 | @end ifnottex |
| 1405 | @tex |
| 1406 | number {\mathsurround=0pt $2n$} |
| 1407 | @end tex |
| 1408 | corresponds to @code{(match-beginning @var{n})}; and |
| 1409 | element |
| 1410 | @ifnottex |
| 1411 | number 2@var{n} + 1 |
| 1412 | @end ifnottex |
| 1413 | @tex |
| 1414 | number {\mathsurround=0pt $2n+1$} |
| 1415 | @end tex |
| 1416 | corresponds to @code{(match-end @var{n})}. |
| 1417 | |
| 1418 | Normally all the elements are markers or @code{nil}, but if |
| 1419 | @var{integers} is non-@code{nil}, that means to use integers instead |
| 1420 | of markers. (In that case, the buffer itself is appended as an |
| 1421 | additional element at the end of the list, to facilitate complete |
| 1422 | restoration of the match data.) If the last match was done on a |
| 1423 | string with @code{string-match}, then integers are always used, |
| 1424 | since markers can't point into a string. |
| 1425 | |
| 1426 | If @var{reuse} is non-@code{nil}, it should be a list. In that case, |
| 1427 | @code{match-data} stores the match data in @var{reuse}. That is, |
| 1428 | @var{reuse} is destructively modified. @var{reuse} does not need to |
| 1429 | have the right length. If it is not long enough to contain the match |
| 1430 | data, it is extended. If it is too long, the length of @var{reuse} |
| 1431 | stays the same, but the elements that were not used are set to |
| 1432 | @code{nil}. The purpose of this feature is to reduce the need for |
| 1433 | garbage collection. |
| 1434 | |
| 1435 | If @var{reseat} is non-@code{nil}, all markers on the @var{reuse} list |
| 1436 | are reseated to point to nowhere. |
| 1437 | |
| 1438 | As always, there must be no possibility of intervening searches between |
| 1439 | the call to a search function and the call to @code{match-data} that is |
| 1440 | intended to access the match data for that search. |
| 1441 | |
| 1442 | @example |
| 1443 | @group |
| 1444 | (match-data) |
| 1445 | @result{} (#<marker at 9 in foo> |
| 1446 | #<marker at 17 in foo> |
| 1447 | #<marker at 13 in foo> |
| 1448 | #<marker at 17 in foo>) |
| 1449 | @end group |
| 1450 | @end example |
| 1451 | @end defun |
| 1452 | |
| 1453 | @defun set-match-data match-list &optional reseat |
| 1454 | This function sets the match data from the elements of @var{match-list}, |
| 1455 | which should be a list that was the value of a previous call to |
| 1456 | @code{match-data}. (More precisely, anything that has the same format |
| 1457 | will work.) |
| 1458 | |
| 1459 | If @var{match-list} refers to a buffer that doesn't exist, you don't get |
| 1460 | an error; that sets the match data in a meaningless but harmless way. |
| 1461 | |
| 1462 | If @var{reseat} is non-@code{nil}, all markers on the @var{match-list} list |
| 1463 | are reseated to point to nowhere. |
| 1464 | |
| 1465 | @findex store-match-data |
| 1466 | @code{store-match-data} is a semi-obsolete alias for @code{set-match-data}. |
| 1467 | @end defun |
| 1468 | |
| 1469 | @node Saving Match Data |
| 1470 | @subsection Saving and Restoring the Match Data |
| 1471 | |
| 1472 | When you call a function that may do a search, you may need to save |
| 1473 | and restore the match data around that call, if you want to preserve the |
| 1474 | match data from an earlier search for later use. Here is an example |
| 1475 | that shows the problem that arises if you fail to save the match data: |
| 1476 | |
| 1477 | @example |
| 1478 | @group |
| 1479 | (re-search-forward "The \\(cat \\)") |
| 1480 | @result{} 48 |
| 1481 | (foo) ; @r{Perhaps @code{foo} does} |
| 1482 | ; @r{more searching.} |
| 1483 | (match-end 0) |
| 1484 | @result{} 61 ; @r{Unexpected result---not 48!} |
| 1485 | @end group |
| 1486 | @end example |
| 1487 | |
| 1488 | You can save and restore the match data with @code{save-match-data}: |
| 1489 | |
| 1490 | @defmac save-match-data body@dots{} |
| 1491 | This macro executes @var{body}, saving and restoring the match |
| 1492 | data around it. The return value is the value of the last form in |
| 1493 | @var{body}. |
| 1494 | @end defmac |
| 1495 | |
| 1496 | You could use @code{set-match-data} together with @code{match-data} to |
| 1497 | imitate the effect of the special form @code{save-match-data}. Here is |
| 1498 | how: |
| 1499 | |
| 1500 | @example |
| 1501 | @group |
| 1502 | (let ((data (match-data))) |
| 1503 | (unwind-protect |
| 1504 | @dots{} ; @r{Ok to change the original match data.} |
| 1505 | (set-match-data data))) |
| 1506 | @end group |
| 1507 | @end example |
| 1508 | |
| 1509 | Emacs automatically saves and restores the match data when it runs |
| 1510 | process filter functions (@pxref{Filter Functions}) and process |
| 1511 | sentinels (@pxref{Sentinels}). |
| 1512 | |
| 1513 | @ignore |
| 1514 | Here is a function which restores the match data provided the buffer |
| 1515 | associated with it still exists. |
| 1516 | |
| 1517 | @smallexample |
| 1518 | @group |
| 1519 | (defun restore-match-data (data) |
| 1520 | @c It is incorrect to split the first line of a doc string. |
| 1521 | @c If there's a problem here, it should be solved in some other way. |
| 1522 | "Restore the match data DATA unless the buffer is missing." |
| 1523 | (catch 'foo |
| 1524 | (let ((d data)) |
| 1525 | @end group |
| 1526 | (while d |
| 1527 | (and (car d) |
| 1528 | (null (marker-buffer (car d))) |
| 1529 | @group |
| 1530 | ;; @file{match-data} @r{buffer is deleted.} |
| 1531 | (throw 'foo nil)) |
| 1532 | (setq d (cdr d))) |
| 1533 | (set-match-data data)))) |
| 1534 | @end group |
| 1535 | @end smallexample |
| 1536 | @end ignore |
| 1537 | |
| 1538 | @node Search and Replace |
| 1539 | @section Search and Replace |
| 1540 | @cindex replacement |
| 1541 | |
| 1542 | If you want to find all matches for a regexp in part of the buffer, |
| 1543 | and replace them, the best way is to write an explicit loop using |
| 1544 | @code{re-search-forward} and @code{replace-match}, like this: |
| 1545 | |
| 1546 | @example |
| 1547 | (while (re-search-forward "foo[ \t]+bar" nil t) |
| 1548 | (replace-match "foobar")) |
| 1549 | @end example |
| 1550 | |
| 1551 | @noindent |
| 1552 | @xref{Replacing Match,, Replacing the Text that Matched}, for a |
| 1553 | description of @code{replace-match}. |
| 1554 | |
| 1555 | However, replacing matches in a string is more complex, especially |
| 1556 | if you want to do it efficiently. So Emacs provides a function to do |
| 1557 | this. |
| 1558 | |
| 1559 | @defun replace-regexp-in-string regexp rep string &optional fixedcase literal subexp start |
| 1560 | This function copies @var{string} and searches it for matches for |
| 1561 | @var{regexp}, and replaces them with @var{rep}. It returns the |
| 1562 | modified copy. If @var{start} is non-@code{nil}, the search for |
| 1563 | matches starts at that index in @var{string}, so matches starting |
| 1564 | before that index are not changed. |
| 1565 | |
| 1566 | This function uses @code{replace-match} to do the replacement, and it |
| 1567 | passes the optional arguments @var{fixedcase}, @var{literal} and |
| 1568 | @var{subexp} along to @code{replace-match}. |
| 1569 | |
| 1570 | Instead of a string, @var{rep} can be a function. In that case, |
| 1571 | @code{replace-regexp-in-string} calls @var{rep} for each match, |
| 1572 | passing the text of the match as its sole argument. It collects the |
| 1573 | value @var{rep} returns and passes that to @code{replace-match} as the |
| 1574 | replacement string. The match-data at this point are the result |
| 1575 | of matching @var{regexp} against a substring of @var{string}. |
| 1576 | @end defun |
| 1577 | |
| 1578 | If you want to write a command along the lines of @code{query-replace}, |
| 1579 | you can use @code{perform-replace} to do the work. |
| 1580 | |
| 1581 | @defun perform-replace from-string replacements query-flag regexp-flag delimited-flag &optional repeat-count map start end |
| 1582 | This function is the guts of @code{query-replace} and related |
| 1583 | commands. It searches for occurrences of @var{from-string} in the |
| 1584 | text between positions @var{start} and @var{end} and replaces some or |
| 1585 | all of them. If @var{start} is @code{nil} (or omitted), point is used |
| 1586 | instead, and the end of the buffer's accessible portion is used for |
| 1587 | @var{end}. |
| 1588 | |
| 1589 | If @var{query-flag} is @code{nil}, it replaces all |
| 1590 | occurrences; otherwise, it asks the user what to do about each one. |
| 1591 | |
| 1592 | If @var{regexp-flag} is non-@code{nil}, then @var{from-string} is |
| 1593 | considered a regular expression; otherwise, it must match literally. If |
| 1594 | @var{delimited-flag} is non-@code{nil}, then only replacements |
| 1595 | surrounded by word boundaries are considered. |
| 1596 | |
| 1597 | The argument @var{replacements} specifies what to replace occurrences |
| 1598 | with. If it is a string, that string is used. It can also be a list of |
| 1599 | strings, to be used in cyclic order. |
| 1600 | |
| 1601 | If @var{replacements} is a cons cell, @code{(@var{function} |
| 1602 | . @var{data})}, this means to call @var{function} after each match to |
| 1603 | get the replacement text. This function is called with two arguments: |
| 1604 | @var{data}, and the number of replacements already made. |
| 1605 | |
| 1606 | If @var{repeat-count} is non-@code{nil}, it should be an integer. Then |
| 1607 | it specifies how many times to use each of the strings in the |
| 1608 | @var{replacements} list before advancing cyclically to the next one. |
| 1609 | |
| 1610 | If @var{from-string} contains upper-case letters, then |
| 1611 | @code{perform-replace} binds @code{case-fold-search} to @code{nil}, and |
| 1612 | it uses the @code{replacements} without altering the case of them. |
| 1613 | |
| 1614 | Normally, the keymap @code{query-replace-map} defines the possible |
| 1615 | user responses for queries. The argument @var{map}, if |
| 1616 | non-@code{nil}, specifies a keymap to use instead of |
| 1617 | @code{query-replace-map}. |
| 1618 | @end defun |
| 1619 | |
| 1620 | @defvar query-replace-map |
| 1621 | This variable holds a special keymap that defines the valid user |
| 1622 | responses for @code{perform-replace} and the commands that use it, as |
| 1623 | well as @code{y-or-n-p} and @code{map-y-or-n-p}. This map is unusual |
| 1624 | in two ways: |
| 1625 | |
| 1626 | @itemize @bullet |
| 1627 | @item |
| 1628 | The ``key bindings'' are not commands, just symbols that are meaningful |
| 1629 | to the functions that use this map. |
| 1630 | |
| 1631 | @item |
| 1632 | Prefix keys are not supported; each key binding must be for a |
| 1633 | single-event key sequence. This is because the functions don't use |
| 1634 | @code{read-key-sequence} to get the input; instead, they read a single |
| 1635 | event and look it up ``by hand.'' |
| 1636 | @end itemize |
| 1637 | @end defvar |
| 1638 | |
| 1639 | Here are the meaningful ``bindings'' for @code{query-replace-map}. |
| 1640 | Several of them are meaningful only for @code{query-replace} and |
| 1641 | friends. |
| 1642 | |
| 1643 | @table @code |
| 1644 | @item act |
| 1645 | Do take the action being considered---in other words, ``yes.'' |
| 1646 | |
| 1647 | @item skip |
| 1648 | Do not take action for this question---in other words, ``no.'' |
| 1649 | |
| 1650 | @item exit |
| 1651 | Answer this question ``no,'' and give up on the entire series of |
| 1652 | questions, assuming that the answers will be ``no.'' |
| 1653 | |
| 1654 | @item act-and-exit |
| 1655 | Answer this question ``yes,'' and give up on the entire series of |
| 1656 | questions, assuming that subsequent answers will be ``no.'' |
| 1657 | |
| 1658 | @item act-and-show |
| 1659 | Answer this question ``yes,'' but show the results---don't advance yet |
| 1660 | to the next question. |
| 1661 | |
| 1662 | @item automatic |
| 1663 | Answer this question and all subsequent questions in the series with |
| 1664 | ``yes,'' without further user interaction. |
| 1665 | |
| 1666 | @item backup |
| 1667 | Move back to the previous place that a question was asked about. |
| 1668 | |
| 1669 | @item edit |
| 1670 | Enter a recursive edit to deal with this question---instead of any |
| 1671 | other action that would normally be taken. |
| 1672 | |
| 1673 | @item delete-and-edit |
| 1674 | Delete the text being considered, then enter a recursive edit to replace |
| 1675 | it. |
| 1676 | |
| 1677 | @item recenter |
| 1678 | Redisplay and center the window, then ask the same question again. |
| 1679 | |
| 1680 | @item quit |
| 1681 | Perform a quit right away. Only @code{y-or-n-p} and related functions |
| 1682 | use this answer. |
| 1683 | |
| 1684 | @item help |
| 1685 | Display some help, then ask again. |
| 1686 | @end table |
| 1687 | |
| 1688 | @node Standard Regexps |
| 1689 | @section Standard Regular Expressions Used in Editing |
| 1690 | @cindex regexps used standardly in editing |
| 1691 | @cindex standard regexps used in editing |
| 1692 | |
| 1693 | This section describes some variables that hold regular expressions |
| 1694 | used for certain purposes in editing: |
| 1695 | |
| 1696 | @defvar page-delimiter |
| 1697 | This is the regular expression describing line-beginnings that separate |
| 1698 | pages. The default value is @code{"^\014"} (i.e., @code{"^^L"} or |
| 1699 | @code{"^\C-l"}); this matches a line that starts with a formfeed |
| 1700 | character. |
| 1701 | @end defvar |
| 1702 | |
| 1703 | The following two regular expressions should @emph{not} assume the |
| 1704 | match always starts at the beginning of a line; they should not use |
| 1705 | @samp{^} to anchor the match. Most often, the paragraph commands do |
| 1706 | check for a match only at the beginning of a line, which means that |
| 1707 | @samp{^} would be superfluous. When there is a nonzero left margin, |
| 1708 | they accept matches that start after the left margin. In that case, a |
| 1709 | @samp{^} would be incorrect. However, a @samp{^} is harmless in modes |
| 1710 | where a left margin is never used. |
| 1711 | |
| 1712 | @defvar paragraph-separate |
| 1713 | This is the regular expression for recognizing the beginning of a line |
| 1714 | that separates paragraphs. (If you change this, you may have to |
| 1715 | change @code{paragraph-start} also.) The default value is |
| 1716 | @w{@code{"[@ \t\f]*$"}}, which matches a line that consists entirely of |
| 1717 | spaces, tabs, and form feeds (after its left margin). |
| 1718 | @end defvar |
| 1719 | |
| 1720 | @defvar paragraph-start |
| 1721 | This is the regular expression for recognizing the beginning of a line |
| 1722 | that starts @emph{or} separates paragraphs. The default value is |
| 1723 | @w{@code{"\f\\|[ \t]*$"}}, which matches a line containing only |
| 1724 | whitespace or starting with a form feed (after its left margin). |
| 1725 | @end defvar |
| 1726 | |
| 1727 | @defvar sentence-end |
| 1728 | If non-@code{nil}, the value should be a regular expression describing |
| 1729 | the end of a sentence, including the whitespace following the |
| 1730 | sentence. (All paragraph boundaries also end sentences, regardless.) |
| 1731 | |
| 1732 | If the value is @code{nil}, the default, then the function |
| 1733 | @code{sentence-end} has to construct the regexp. That is why you |
| 1734 | should always call the function @code{sentence-end} to obtain the |
| 1735 | regexp to be used to recognize the end of a sentence. |
| 1736 | @end defvar |
| 1737 | |
| 1738 | @defun sentence-end |
| 1739 | This function returns the value of the variable @code{sentence-end}, |
| 1740 | if non-@code{nil}. Otherwise it returns a default value based on the |
| 1741 | values of the variables @code{sentence-end-double-space} |
| 1742 | (@pxref{Definition of sentence-end-double-space}), |
| 1743 | @code{sentence-end-without-period} and |
| 1744 | @code{sentence-end-without-space}. |
| 1745 | @end defun |
| 1746 | |
| 1747 | @ignore |
| 1748 | arch-tag: c2573ca2-18aa-4839-93b8-924043ef831f |
| 1749 | @end ignore |