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Re: OS X vs. My Regex

by tall_man (Parson)
on Apr 16, 2003 at 19:04 UTC ( #251003=note: print w/replies, xml ) Need Help??

in reply to OS X vs. My Regex

You are making the regular expression engine do a lot of extra work by:

1) Using capturing parenthesis instead of noncapturing ones .
2) Even a non-greedy dot-star is bad (see Death to Dot Star!). Use a negated character class like [^\]]* instead.
3) Excessive going in and out from parenthesis levels, as in the [^\[] expression following the "|", which ought to have a "+" after it.

These inefficiencies are probably causing the regular expression engine to go wild and run out of memory. By the way, why not use module Text:Balanced instead?

Update: Here is a brushed-up version with my suggestions added:

if ($text =~ /^ (?: # Any amount of: (?: \[ # An open brace [^\]]* # Any amount of non-brace stuff \] # A close brace ) | # Or [^\[]+ # Anything that's not an open brac +e. )* \] # Followed by a close brace /xs

Update2: After recommending Text::Balanced for this problem, I decided to try it for myself. I would have expected the following code to work, but it doesn't (I get the error: and it does work as long as you test for the following message as an acceptable case: "Did not find opening bracket after prefix: "[^\[]*", detected at offset 1216". The message just means you have passed all the brackets, which is fine.

my $next; while ( $next = (extract_bracketed($text,'[]','[^\[]*'))[0] ) { print "found matching brackets: *$next*\n"; } print "found bracket error: $@\n" if $@;

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Re: Re: OS X vs. My Regex
by Pedro Picasso (Sexton) on Apr 17, 2003 at 15:57 UTC
    Thanks. Your example was helpful, and I'd never heard of Text::Balanced before. My expressions will not be such hogs in the future.
    -the Pedro Picasso
    (sourceCode == freeSpeech)

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