in reply to Matching backslash in regexp negative lookbehind

Here's a single-pass alternative to this (uses the same test-vector set): 

BEGIN {

    my %mask = ( q{"} => q{"***"},  q{'} => q{'***'}, );

    my $connector = qr{ => | : }xms;

    sub elide {

        my ($key,     # pattern: arm sensitive sub-string elision
            $string,
            ) = @_;

        $string =~ s{
            ((?<! \\) ['"]) $key \g-1 \s*
            $connector \s*
            \K
            \g-1 ((?! \g-2 | \\) .)* (?: \\. (?2)*)* \g-2
            }
            {$mask{$1}}xmsg;

        return $string;

        }

    }  # end BEGIN block

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Whether this variation is preferable is very much a matter of taste. The  BEGIN block is required so that certain scalars | lexicals (the  %mask hash in particular,  $connector not so much since it could easily be inlined) will be guaranteed to be properly initialized. Very much dependent on 5.10 regex extensions.

Give a man a fish:  <%-{-{-{-<

In Section Seekers of Perl Wisdom