regex using negative look ahead assertion

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

Hello Monks,

i am new to perl and i am having a doubt in a regex.

The text looks as follows

<PrimaryIE id="10001">organisation structure<pg>2.3, 4.5, 6.8</pg></PrimaryIE>

I want to get the pg tag contents and some more informations from the above text. i want to write a regular expression using negative look ahead assertion for the above case

i wrote the regex like the one that follows. is this right or not

$str =~ /<PrimaryIE id="[^\"]+">.*(?!<pg>)<pg>(.*?)<\/pg><\/PrimaryIE>/gsi

20040701 Edit by castaway: Changed title from 'regex'

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Re: regex using negative look ahead assertion by diotalevi (Canon) on Jun 26, 2004 at 11:38 UTC
This is better handled with XPath. `m( <pg [^>]* > # A <pg> tag with optional body ( # Capture START (?: # Skip past all the non-tag-beginng-like things but be sure # not to allow backtracking. (?> [^<]+ ) \| # OR # Match something like a tag beginning as long as it # isn't an opening for <pg < (?! pg\s ) ) ) # Capture END </pg> )x;` [download]	[reply] [d/l]

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Re: regex using negative look ahead assertion
by diotalevi (Canon) on Jun 26, 2004 at 11:38 UTC

This is better handled with XPath.

m( <pg [^>]* > # A <pg> tag with optional body
   ( # Capture START
       (?:
           # Skip past all the non-tag-beginng-like things but be sure
           # not to allow backtracking.
           (?> [^<]+ )
           | # OR
           # Match something like a tag beginning as long as it
           # isn't an opening for <pg
           < (?! pg\s )
       )
   ) # Capture END
   </pg> )x;
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