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i think this will work for you:
Based upon this test code to try to match ab followed by 4 bytes w/no ab sequence:
perl -le 'print for map { /ab(?!ab)(.(?!ab)){2}.{2}/s ? $& : () } @AR +GV' abhjabdf abasdasd abdasdadsab ababblah OUTPUTS: abasda abdasd abblah
Update: Here's a commented version:
/ \x26\x67 # Starting sequence (let's call it AB) (?!\x26\x67) # Exclude double starting seqeuence, e.g. ABAB (?: # non-capture .(?!\x26\x67) # Any character that's not followed by the sequenc +e ){6} # Need N-2 of these .{2} # And the last two characters can be anything. # note we know they're not AB because otherwise the # (N-2)th item in the previous part wouldn't have mat +ched /sx # Enable comments, and make . mean everything
Update: Here's a generic version:
my $marker = '&g'; my $N = 8; my $n1 = $N-2; /$marker(?!$marker)(?:.(?!$marker)){$n1}.{2}/s
Update: (As pointed out by diotalevi) Added the /s modifier in case the data stream can have a newline in it.

In reply to Re: regex for negating a sequence by davidrw
in thread regex for negating a sequence by spurperl

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