in reply to Re: Replace only unescaped metachars
in thread Replace only unescaped metachars

Close, but no cigar 
my $string = '\\\\\\a';
# Unprocessed: \\\a
# Should be:   \a
# Result:      \\a

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my $string = '\\\\\\?';
# Unprocessed: \\\?
# Should be:   \?
# Result:      \\#

[download]

See my top-level reply for a solution.

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Re^3: Replace only unescaped metachars
by Anno (Deacon) on Feb 22, 2007 at 18:17 UTC
    Yes, I knew it had limitations which are hard to fix in an s/// approach.

    The recognition of escaped escapes is a naturally recursive problem. Regular expressions, even Perl's, are notoriously bad at that. Your remark about wanting a parser is spot on.

    Anno

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[d/l]
      There's no recursion here (which is why the OP's parser is really just a tokeniser). The problem is capturing repeatedly, and knowing which rule (regexp piece) captured a given capture.
[reply]
        The recursion I vaguely had in mind was 
        my $escape;
$escape       = qr/(?<!(??{ $escape}))\\/;

        [download]
        It fails, of course, because it would require variable-length lookbehind.

        Anno

[reply]
[d/l]

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