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Re^7: Regex problems using '|'

by JavaFan (Canon)
on Jul 22, 2008 at 12:45 UTC ( [id://699294] : note . print w/replies, xml ) Need Help??


in reply to Re^6: Regex problems using '|'
in thread Regex problems using '|'

Your expectation is that if you have /pat1|pat2/, the regexp engine will first try to find 'pat1' anywhere in the string, and only then pat2.

That's not how the regexp engine works. Instead, it will find pat1 or pat2, whichever comes first (leftmost) in the string. Only if the first occurrences of pat1 and pat2 start at the same character, the order of | becomes important: the engine will pick the leftmost.

Now, in your example, pat2 is a pattern that matches at the beginning of the string, while pat1 doesn't. So pat2 matches, not pat1.

If you want pat1 to match if it occurs in the string, and only if pat1 doesn't match, you want pat2, use two different patterns:

$str =~ /pat1/ or $str =~ /pat2/;
Alternatively, make it that pat1 starts matching at the beginning of the string as well:
$vulnerabilityText =~ m/^.+?Remediation Report\n\n(.+?)\n|^(.+?)\n/;

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Re^8: Regex problems using '|'
by romandas (Pilgrim) on Jul 22, 2008 at 13:05 UTC

    Ah.

    Now moritz's other reply makes sense. Thanks! That's what I needed to know.

    I expected the regex engine's '|' to work like the 'or' or '||' operators. So much for that. ;)