According to perdoc, the "//" regexp does mean to inherit pervious match.
So for me, line3 and line4 shall give the same result. Thus the second case is correct, while the first one doesn't make sense. And your example also reflects this inherit process. Sincerely Pine -----Original Message----- From: Tom Allison [mailto:[EMAIL PROTECTED] Sent: Friday, July 29, 2005 3:23 PM To: beginners@perl.org Subject: Re: regular expression match question Pine Yan wrote: > A script like this: > > line1: $string3 = "bacdeabcdefghijklabcdeabcdefghijkl"; > line2: $string4 = "xxyyzzbatttvv"; > > line3: print "\$1 = $1 [EMAIL PROTECTED],$+[0]}, \$& = $&\n" > if($string3 > =~ /(a|b)*/); > line4: print "\$1 = $1 [EMAIL PROTECTED],$+[0]}, \$& = $&\n" > if($string4 > =~ //); > > Run and gett result: > > $1 = a @{0,2}, $& = ba > $1 = @{0,0}, $& = > > line 3: you are matching the last single letter of the first match [ ^ba ] as $1. @+ and @- merely point to the starting points on that string $string3 being characters 1 and 3 (in array-speak it's 0,2) and from perldocs you can find what $& is all about. If you wanted to match either 'ab' or 'ba' you would do it this way: (ab|ba) to require two letters. > If I change the code of line3 to: > > print "\$1 = $1 [EMAIL PROTECTED],$+[0]}, \$& = $&\n" if($string3 =~ > /(a|b)+/); > > and keep everything else the same, I will get: > > $1 = a @{0,2}, $& = ba > $1 = a @{6,8}, $& = ba I think you are right in that this doesn't make sense right away. It appears that the second expression is returning a match for the previous regex and not a regex of //. So I don't think that the statement of $string =~ // is going to return the first element '', rather it returns the last regex that was applied. RUN THIS $string3="This is my favorite day."; $string4="Some days are better than others."; print $-[0],"\n" if $string4 =~ //; print $-[0],"\n" if $string4 =~ /day/; print $-[0],"\n" if $string3 =~ //; print $-[0],"\n" if $string3 =~ /day/; and you get 0 5 20 20 0 because there is no regex expression defined. but the first '20' acts as if you were matching the last expression run (/day/). Question: Bug or Feature? -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] <http://learn.perl.org/> <http://learn.perl.org/first-response> -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] <http://learn.perl.org/> <http://learn.perl.org/first-response>
