in reply to Replace only unescaped metachars

It can be done (at least approximated) in a somewhat more traditional s///g manner, but I'd use two substitutions to deal first with metacharacters, then unescaping. 
my $escape       = qr/(?<!\\)\\/;
my $meta_char    = qr/(?<!$escape)[?*]/;

no warnings 'qw';
my %meta = qw(
    ? #
    * ?
);

my $result = my $string = 't?e\\\\xt\\\\* with e\\scapes\\*';
$result =~ s/($meta_char)/$meta{ $1}/g;
$result =~ s/$escape(.)/$1/gs or die;

print "$string\n";
print "$result\n";

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It transforms the example string in the same way as your code. I wouldn't swear that it does for all input strings.

Anno

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Re^2: Replace only unescaped metachars
by ikegami (Patriarch) on Feb 22, 2007 at 17:53 UTC
    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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[d/l]
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      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.
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