FAQ 6.9 How can I quote a variable to use in a regex?
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From: Phred Phungus on 29 Mar 2010 20:54 J�rgen Exner wrote: > Phred Phungus <Phred(a)example.invalid> wrote: >> PerlFAQ Server wrote: >>> This is an excerpt from the latest version perlfaq6.pod, which >>> comes with the standard Perl distribution. These postings aim to >>> reduce the number of repeated questions as well as allow the community >>> to review and update the answers. The latest version of the complete >>> perlfaq is at http://faq.perl.org . >>> >>> -------------------------------------------------------------------- >>> >>> 6.9: How can I quote a variable to use in a regex? >>> >>> The Perl parser will expand $variable and @variable references in >>> regular expressions unless the delimiter is a single quote. Remember, >>> too, that the right-hand side of a "s///" substitution is considered a >>> double-quoted string (see perlop for more details). Remember also that >>> any regex special characters will be acted on unless you precede the >>> substitution with \Q. Here's an example: >>> >>> $string = "Placido P. Octopus"; >>> $regex = "P."; >>> >>> $string =~ s/$regex/Polyp/; >>> # $string is now "Polypacido P. Octopus" >>> >>> Because "." is special in regular expressions, and can match any single >>> character, the regex "P." here has matched the <Pl> in the original >>> string. >>> >> Am I then correct that a period is not a character? > > ??? > How did you come to that conclusion? Because the regex would then match the middle initial and the string would be "Polypacido Polyp Octopus". -- fred
From: J�rgen Exner on 29 Mar 2010 21:13 Phred Phungus <Phred(a)example.invalid> wrote: >J�rgen Exner wrote: >> Phred Phungus <Phred(a)example.invalid> wrote: >>> PerlFAQ Server wrote: >>>> $string = "Placido P. Octopus"; >>>> $regex = "P."; >>>> >>>> $string =~ s/$regex/Polyp/; >>>> # $string is now "Polypacido P. Octopus" >>>> >>>> Because "." is special in regular expressions, and can match any single >>>> character, the regex "P." here has matched the <Pl> in the original >>>> string. >>>> >>> Am I then correct that a period is not a character? >> >> How did you come to that conclusion? > >Because the regex would then match the middle initial and the string >would be "Polypacido Polyp Octopus". No, it wouldn't because there is no /g modifier in the s///-operation. jue
From: Uri Guttman on 29 Mar 2010 22:39 >>>>> "R" == Ruud <rvtol+usenet(a)xs4all.nl> writes: R> Uri Guttman wrote: >> Ruud: >>> Uri: >>>> i generally use \. but [.] is ok imo. >>> >>> The performance loss was lifted in 5.10, IIRC. >> >> i wasn't concerned with performance but style. the hex version of . is >> what i never want to see. i don't need to look up hex codes to see you >> are trying to match a literal . :) R> Don't shoot the messenger. :) R> I don't understand why you reply on content that was no longer there. R> And you are repeating what you expressed before. R> I also don't understand why you assume that I addressed any concern of R> yours. R> I merely stated a "fact". (but it could be in 5.10.1 or later too) ok, i will admit i am lost as what is going on in this thread anymore and give up on it. no loss. uri -- Uri Guttman ------ uri(a)stemsystems.com -------- http://www.sysarch.com -- ----- Perl Code Review , Architecture, Development, Training, Support ------ --------- Gourmet Hot Cocoa Mix ---- http://bestfriendscocoa.com ---------
From: Ilya Zakharevich on 30 Mar 2010 00:29 On 2010-03-29, Uri Guttman <uri(a)StemSystems.com> wrote: >>>>>> "R" == Ruud <rvtol+usenet(a)xs4all.nl> writes: > > R> Steve M wrote: > >> To access a literal '.' you need to backslash it > > R> Or quotemeta it, or put it in a character class, or mention it as > R> \x2E, etc., etc. > > i would never encode a literal . as \2e. too obscure and what about > unicode (not that i am anything but an ascii bigot! :)? What about unicode? Puzzled, Ilya
From: Ilya Zakharevich on 30 Mar 2010 00:32
On 2010-03-29, Uri Guttman <uri(a)StemSystems.com> wrote: > i wasn't concerned with performance but style. the hex version of . is > what i never want to see. i don't need to look up hex codes to see you > are trying to match a literal . :) May be "needed" (in the sense: more readable than alternatives, and more shell-neutral) in a one-liner to protect "pesky" shell meta-characters (such as % in DOSISH shells, and ! in tcsh)... Yours, Ilya |