* spelling fixes * Why does using $&, $`, or $' slow my program down? + Anno Siegel updated the answer for recent speed modifications
Index: perlfaq6.pod =================================================================== RCS file: /cvs/public/perlfaq/perlfaq6.pod,v retrieving revision 1.33 diff -u -d -r1.33 perlfaq6.pod --- perlfaq6.pod 4 Jun 2005 04:12:40 -0000 1.33 +++ perlfaq6.pod 2 Aug 2005 22:24:57 -0000 @@ -603,7 +603,7 @@ "Perler" # no word char before P, but one after l You don't have to use \b to match words though. You can look for -non-word characters surrrounded by word characters. These strings +non-word characters surrounded by word characters. These strings match the pattern /\b'\b/. "don't" # the ' char is surrounded by "n" and "t" @@ -633,14 +633,20 @@ (contributed by Anno Siegel) Once Perl sees that you need one of these variables anywhere in the -program, it provides them on each and every pattern match. That means -that on every pattern match the entire string will be copied, part of -it to $`, part to $&, and part to $'. Thus the penalty is most severe -with long strings and patterns that match often. Avoid $&, $', and $` -if you can, but if you can't, once you've used them at all, use them -at will because you've already paid the price. Remember that some -algorithms really appreciate them. As of the 5.005 release, the $& -variable is no longer "expensive" the way the other two are. +program, it provides them on each and every pattern match. That means +that on every pattern match the entire string will be copied, part of it +to $`, part to $&, and part to $'. Thus the penalty is most severe with +long strings and patterns that match often. Avoid $&, $', and $` if you +can, but if you can't, once you've used them at all, use them at will +because you've already paid the price. Remember that some algorithms +really appreciate them. As of the 5.005 release, the $& variable is no +longer "expensive" the way the other two are. + +Since Perl 5.6.1 the special variables @- and @+ can functionally replace +$`, $& and $'. These arrays contain pointers to the beginning and end +of each match (see perlvar for the full story), so they give you +essentially the same information, but without the risk of excessive +string copying. =head2 What good is C<\G> in a regular expression? -- brian d foy, [EMAIL PROTECTED]
