I think you've basically got it right.

/^somebegin(?!something)someend$/

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Should work. The only complexity involves lookahead vs. backtrack and because you have stuff both before and after the stuff you don't want, that won't matter (in terms of the truth of the statement, I have no idea about the efficiency).

Personally, if I'm confused by something like this I opt for the slow but readable...

if ( /^somebegin(.*)someend$/ ) {
    my $middle = $1;
    if ( $middle !~ /^something$/ ) {
        # woot
    }
}

[download]

In reply to Re: regex: something...(!something)...something by pileofrogs
in thread regex: something...(!something)...something by aaaone

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