Storing regexps in variables

pando has asked for the wisdom of the Perl Monks concerning the following question:

Hi all, I have a problem with regexp and I have no idea how to overcome this. I have some experience with regexp but this is beyond my knowledge. Looks like ++ from my substring is the problem, but still, how can I do this regexp ?

$substr="libstdc++"
$string="compat-libstdc++.so.6"
print "Found" if ( $string =~ /$substr/ );
[download]

I get an error:

Nested quantifiers in regex; marked by <-- HERE in m/compat-libstdc++ 
+<-- HERE }/ at
[download]

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Re: Storing regexps in variables by davorg (Chancellor) on Mar 16, 2007 at 12:53 UTC
A '+' has a special meaning in a regular expression (it means "one or more of the preceding character"). Two of them in succession is a regex syntax error. Your problem is that you have regex metacharacters that you want to be treated as normal characters. That is what the \Q escape sequence is for. `print "Found" if $string =~ /\Q$substr/;` [download] -- <http://dave.org.uk> "The first rule of Perl club is you do not talk about Perl club." -- Chip Salzenberg	[reply] [d/l]
Re: Storing regexps in variables by Util (Priest) on Mar 16, 2007 at 13:21 UTC
I think you left out the 'd' in the second line of your example code; Did you mean to say `$string="compat-libstdc++.so.6";` ? The other monks are correct about quotemeta and \Q to fix your regex problem. Also, consider using index, which is designed for just finding one string in another. `print "Found" if index( $string, $substr ) != -1;` [download]	[reply] [d/l] [select]
Re: Storing regexps in variables by andye (Curate) on Mar 16, 2007 at 12:52 UTC
Take a look at quotemeta. Hope that helps, andye	[reply]
Re: Storing regexps in variables by pando (Initiate) on Mar 16, 2007 at 20:42 UTC
Yes indeed, it was a typo error and I missed a 'd' in my message. Anyway, thank you information was really helpful and did the trick.	[reply]