how to use "NOT" in regex

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

Hello
I'm trying to match (for replace) a text line that doesn't start with one of two words.
The only thing about "not" I could find for replace purposes in regex was the ^abc.. syntax
which only match 1 char and never longer strings.
Is there a way to do this ?
I'm expecting something like s/ \n !($word1|$word2) .* \n / $replacement /x
or maybe something like s/ $ !($word1|$word2) .* \n / $replacement /x
or maybe even s/ ^ ($word1|$word2){0} .* \n / $replacement /x
am I close ?
There got to be a better way.
thx

Comment on how to use "NOT" in regex

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Re: how to use "NOT" in regex by wind (Priest) on Mar 23, 2011 at 20:33 UTC
Use a zero width negative look-ahead assertion. perlre `/^(?!$word1\|$word2).../` [download] Also, you might want to escape the "words" for regex special characters using quotemeta. `/^(?!\Q$word1\E\|\Q$word2\E).../` [download]	[reply] [d/l] [select]
Re: how to use "NOT" in regex by mellon85 (Monk) on Mar 23, 2011 at 23:34 UTC
can't you match the strings that start with those two words and then negate the condition? makes more sense to me as a regexp `if (!/^($word1\|$word2)/) { # code }` [download]	[reply] [d/l]