I want to create a regex that will identify a string surrounded by quotes, and remove the quotes. If the quote symbol appears within the string, the match should fail.
The quotes can be either ' or ". Eventually they might be multi-character strings (e.g. '').
I'm not concerned at this point about recognizing escaped embedded quotes.
This is slightly contrived .. I mostly want to understand why a negative lookahead isn't working the way I thought it would.
I sure would appreciate being shown what I'm misunderstanding.
#!/usr/bin/env perl
use warnings;
use strict;
my @cases = (
q{'abc"def'},
q{'abc'},
q{"abc"},
q{''},
q{'abc'def'}, # Want this to fail matching
q{'This shouldn't match'}, # Want this to fail matching
q{"This isn't a problem"},
q{"abc},
q{abc"},
q{abc},
q{'abc"},
q{'ab''}, # Want this to fail matching
);
strip_quotes($_) for @cases;
# If we can remove a matching pair of single or double quotes from
# a string, without the quote symbol also appearing within the string,
# do so. Otherwise don't change the string.
sub strip_quotes {
my $line = shift;
print "\n$line\n";
# NO NEGATIVE LOOKAHEAD
# This works except it allows an embedded delimiter
if ( $line =~ m{^ # anchor
( # capture delimiter in pos 1
["'] # delim is single or double quote
)
(.*) # anything
\g1$}x # finally, the delim
) {
print " 1- Got a match: delimiter was {$1}, body was {$2}\n";
}
else {
print " 1- No match.\n";
}
# ATTEMPTING NEGATIVE LOOKAHEAD
# This should fail if the delimiter is found in non-terminal pos.
if ( $line =~ m{^ # anchor
( # capture delimiter in pos 1
["'] # delim is single or double quote
)
(.*(?!\g1)) # neg lookahead for delim
\g1$}x # finally, the delim
) {
print " 2- Got a match: delimiter was {$1}, body was {$2}\n";
}
else {
print " 2- No match.\n";
}
}
Result:
'abc"def'
1- Got a match: delimiter was {'}, body was {abc"def}
2- No match.
'abc'
1- Got a match: delimiter was {'}, body was {abc}
2- No match.
"abc"
1- Got a match: delimiter was {"}, body was {abc}
2- No match.
''
1- Got a match: delimiter was {'}, body was {}
2- No match.
'abc'def'
1- Got a match: delimiter was {'}, body was {abc'def}
2- No match.
'This shouldn't match'
1- Got a match: delimiter was {'}, body was {This shouldn't match}
2- No match.
"This isn't a problem"
1- Got a match: delimiter was {"}, body was {This isn't a problem}
2- No match.
"abc
1- No match.
2- No match.
abc"
1- No match.
2- No match.
abc
1- No match.
2- No match.
'abc"
1- No match.
2- No match.
'ab''
1- Got a match: delimiter was {'}, body was {ab'}
2- No match.
