Error! Nested quantifiers in regex

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

Hi monks,
I am checking list of email subjects for a certain values. I want to ignore all RE, FW at the begining. I used following code:

$match_count += 1 if ($subject =~ /^[RE:\s*|FW:\s*]*$match_string\i*$/
+);
[download]

When I passed $match_string = "Are you a Perfect Sinhalese????" it gives following error:

Nested quantifiers in regex; marked by <-- HERE in m/^[RE:\s*|FW:\s*]*
+Are you a Perfect Sinhalese??? 
<-- HERE ?\s*$/ at C:/Perl/lib/LTG/DocBuddy/Relation.pm line 496.
[download]

Code at line 496 is given above. But it works fine with $match_string = "Are you a Perfect Sinhalese". What's the problem here? And how I can avoid it?
Thanks - SB

update (broquaint): s{<(/)?pre>}(<${1}code>)g

Comment on Error! Nested quantifiers in regex Select or Download Code

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Re: Error! Nested quantifiers in regex by Abigail-II (Bishop) on Sep 16, 2003 at 09:06 UTC
`?` is special for the regexp machine. What you want is: `/^(?:RE:\s\|FW:\s)\Q$match_string\E$/` [download] The `\Q ... \E` tells the regexp engine that anything in between should be taken "as is". I also removed the `\i`. I do not know what you think `\i` is, but any string will end with zero or more of them. Finally, one uses `( )` or `(?: )` for grouping, `[RE:\s\|FW:\s]*` means something else. That would match any string consisting of whitespace, the capital letters E, F, R, W and the characters : and \|. Abigail	[reply] [d/l] [select]
Re: Re: Error! Nested quantifiers in regex by banduwgs (Beadle) on Sep 16, 2003 at 09:16 UTC
Thank you, that's right. It works. Oh, "i" is a mistake, I don't have it in my code - SB	[reply]
Re: Error! Nested quantifiers in regex by leriksen (Curate) on Sep 16, 2003 at 09:12 UTC
a ? means that the preceding character or group is optional - a ? is called a qualifier - so Sinhalese? mean that Sinhales and Sinhalese will match. however ???? means that the ? quantifiers are applying to each other - nested in other words, and that is not allowed in Perl's regex implementation	[reply]