Re^2: negative lookbehind and VERY strange capture

Hello Corion

Thank you very much for your suggestion! It helps a lot!

my @tests = (
  '"abcd\\\\efgh"',
  '"abcd\\""',
  '"abcd\\"efgh"',
  '"abcd\\\\\\"efgh"',
  '"abcd\\\\i\\"efgh"',
  '"abcd\\\\"',
);

foreach my $test (@tests) {
  print "Try for \"$test\":\n";
  if ($test =~ /^"((?:[^"\\]|\\["\\])+)"$/) {
    print "It matches!\n";
    print '$1: ' . $1 . "\n";
    print '$2: ' . (defined($2) ? "\$2 is defined\n" : "\$2 is NOT def
+ined\n");
  } else {
    print "It does not match!\n";
  }
  print "\n";
}
[download]

Result:

Try for ""abcd\\efgh"":
It matches!
$1: abcd\\efgh
$2: $2 is NOT defined

Try for ""abcd\""":
It matches!
$1: abcd\"
$2: $2 is NOT defined

Try for ""abcd\"efgh"":
It matches!
$1: abcd\"efgh
$2: $2 is NOT defined

Try for ""abcd\\\"efgh"":
It matches!
$1: abcd\\\"efgh
$2: $2 is NOT defined

Try for ""abcd\\i\"efgh"":
It matches!
$1: abcd\\i\"efgh
$2: $2 is NOT defined

Try for ""abcd\\"":
It matches!
$1: abcd\\
$2: $2 is NOT defined
[download]

Best regards

Denis

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Re^3: negative lookbehind and VERY strange capture by hippo (Archbishop) on Sep 18, 2016 at 16:12 UTC
Glad to hear you have a working solution. Might I also suggest that for test scripts like this you consider using one of the Test::* frameworks? They will help to highlight where your matches fail. Here's an example using the ubiquitous Test::More to show how simple it would be to integrate. #!/usr/bin/perl use strict; use warnings; use Test::More; # Set up source strings (keys) and expected results (values) my %tests = ( '"abcd\\\\efgh"' => 'abcd\\\\efgh', '"abcd\\""' => 'abcd\\"', '"abcd\\"efgh"' => 'abcd\\"efgh', '"abcd\\\\\\"efgh"' => 'abcd\\\\\\"efgh', '"abcd\\\\i\\"efgh"' => 'abcd\\\\i\\"efgh', '"abcd\\\\"' => 'abcd\\\\' ); # Set the total number of tests to perform plan tests => 3 * keys %tests; while ( my ($test, $exp) = each %tests) { ok ($test =~ /^"((?:[^"\\]\|\\["\\])+)"$/, "$test matches"); is ($1, $exp, "\$1 is $exp"); is ($2, undef, '$2 is undefined'); } [download] If any of the tests fail it is easier to spot than having to visually parse the script output. You can also run `prove` on the script to get just a summary which is even clearer. If you write a lot of scripts like this, it is well worth becoming familiar with the wealth of testing modules available.	[reply] [d/l] [select]
Re^3: negative lookbehind and VERY strange capture by AnomalousMonk (Archbishop) on Sep 18, 2016 at 18:31 UTC
FWIW, please note that `/^"((?:[^"\\]\|\\["\\])+)"$/` does not match the empty string: `c:\@Work\Perl\monks>perl -wMstrict -le "my $emptystring = '\"\"'; print '+ match' if $emptystring =~ /^\"((?:[^^\"\\]\|\\[\"\\])+)\"$/; print '* match' if $emptystring =~ /^\"((?:[^^\"\\]\|\\[\"\\]))\"$/; " match` [download] (Please forgive all the extra backslashes and ignore the extra `^` in `[^^\"\\]`. These are Windoze command line artifacts.) Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]