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comparison man/lispref/searching.texi @ 442:abe6d1db359e r21-2-36

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Import from CVS: tag r21-2-36
author cvs
date Mon, 13 Aug 2007 11:35:02 +0200
parents 3ecd8885ac67
children 576fb035e263
comparison
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441:72a7cfa4a488 442:abe6d1db359e
271 works just like @samp{*}, except that rather than matching the longest 271 works just like @samp{*}, except that rather than matching the longest
272 match, it matches the shortest match. @samp{*?} is known as a 272 match, it matches the shortest match. @samp{*?} is known as a
273 @dfn{non-greedy} quantifier, a regexp construct borrowed from Perl. 273 @dfn{non-greedy} quantifier, a regexp construct borrowed from Perl.
274 @c Did perl get this from somewhere? What's the real history of *? ? 274 @c Did perl get this from somewhere? What's the real history of *? ?
275 275
276 This construct very useful for when you want to match the text inside a 276 This construct is very useful for when you want to match the text inside
277 pair of delimiters. For instance, @samp{/\*.*?\*/} will match C 277 a pair of delimiters. For instance, @samp{/\*.*?\*/} will match C
278 comments in a string. This could not be achieved without the use of 278 comments in a string. This could not easily be achieved without the use
279 greedy quantifier. 279 of a non-greedy quantifier.
280 280
281 This construct has not been available prior to XEmacs 20.4. It is not 281 This construct has not been available prior to XEmacs 20.4. It is not
282 available in FSF Emacs. 282 available in FSF Emacs.
283 283
284 @item +? 284 @item +?
285 @cindex @samp{+?} in regexp 285 @cindex @samp{+?} in regexp
286 is the @samp{+} analog to @samp{*?}. 286 is the non-greedy version of @samp{+}.
287
288 @item ??
289 @cindex @samp{??} in regexp
290 is the non-greedy version of @samp{?}.
287 291
288 @item \@{n,m\@} 292 @item \@{n,m\@}
289 @c Note the spacing after the close brace is deliberate. 293 @c Note the spacing after the close brace is deliberate.
290 @cindex @samp{\@{n,m\@} }in regexp 294 @cindex @samp{\@{n,m\@} }in regexp
291 serves as an interval quantifier, analogous to @samp{*} or @samp{+}, but 295 serves as an interval quantifier, analogous to @samp{*} or @samp{+}, but
292 specifies that the expression must match at least @var{n} times, but no 296 specifies that the expression must match at least @var{n} times, but no
293 more than @var{m} times. This syntax is supported by most Unix regexp 297 more than @var{m} times. This syntax is supported by most Unix regexp
294 utilities, and has been introduced to XEmacs for the version 20.3. 298 utilities, and has been introduced to XEmacs for the version 20.3.
299
300 Unfortunately, the non-greedy version of this quantifier does not exist
301 currently, although it does in Perl.
295 302
296 @item [ @dots{} ] 303 @item [ @dots{} ]
297 @cindex character set (in regexp) 304 @cindex character set (in regexp)
298 @cindex @samp{[} in regexp 305 @cindex @samp{[} in regexp
299 @cindex @samp{]} in regexp 306 @cindex @samp{]} in regexp
460 is called a @dfn{shy} grouping operator, and it is used just like 467 is called a @dfn{shy} grouping operator, and it is used just like
461 @samp{\( @dots{} \)}, except that it does not cause the matched 468 @samp{\( @dots{} \)}, except that it does not cause the matched
462 substring to be recorded for future reference. 469 substring to be recorded for future reference.
463 470
464 This is useful when you need a lot of grouping @samp{\( @dots{} \)} 471 This is useful when you need a lot of grouping @samp{\( @dots{} \)}
465 constructs, but only want to remember one or two. Then you can use 472 constructs, but only want to remember one or two -- or if you have
466 not want to remember them for later use with @code{match-string}. 473 more than nine groupings and need to use backreferences to refer to
474 the groupings at the end.
467 475
468 Using @samp{\(?: @dots{} \)} rather than @samp{\( @dots{} \)} when you 476 Using @samp{\(?: @dots{} \)} rather than @samp{\( @dots{} \)} when you
469 don't need the captured substrings ought to speed up your programs some, 477 don't need the captured substrings ought to speed up your programs some,
470 since it shortens the code path followed by the regular expression 478 since it shortens the code path followed by the regular expression
471 engine, as well as the amount of memory allocation and string copying it 479 engine, as well as the amount of memory allocation and string copying it
472 must do. The actual performance gain to be observed has not been 480 must do. The actual performance gain to be observed has not been
473 measured or quantified as of this writing. 481 measured or quantified as of this writing.
474 @c This is used to good advantage by the font-locking code, and by 482 @c This is used to good advantage by the font-locking code, and by
475 @c `regexp-opt.el'. ... It will be. It's not yet, but will be. 483 @c `regexp-opt.el'.
476 484
477 The shy grouping operator has been borrowed from Perl, and has not been 485 The shy grouping operator has been borrowed from Perl, and has not been
478 available prior to XEmacs 20.3, nor is it available in FSF Emacs. 486 available prior to XEmacs 20.3, nor is it available in FSF Emacs.
479 487
480 @item \w 488 @item \w