Use a zero width negative look-ahead assertion. perlre 
/^(?!$word1|$word2).../

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Also, you might want to escape the "words" for regex special characters using quotemeta. 
/^(?!\Q$word1\E|\Q$word2\E).../

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In reply to Re: how to use "NOT" in regex by wind
in thread how to use "NOT" in regex by palkia

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