Hi Monks

I'm continuing my exploration of Perl and currently exploring regular expressions.

For this simple test, I have a small string of KEY=value pairs, separated by ';' characters. I am trying to identify if a particular KEY has a certain value and a different KEY does not contain a value.

I have code which follows which does this with two regexs:

#!/usr/bin/env perl
use strict;
use warnings;
use 5.016;

for (<DATA>) {
    chomp;
    print "Match: $_\n" if /name=bob/ and not /flags=.*?cat.*?;/;
}

__DATA__
name=bob;flags=human;age=10
name=tiddles;flags=cat,black;age=3
name=bob;flags=cat,white;age=6

[download]

In this simple example, I'm looking to get the line which matches a name of 'bob' and flags does not contain 'cat'. This code works and returns the single matching line.

However, I tried combining the regexes and using lookaheads to match multiple conditions, but this is currently failing. My code for this follows

#!/usr/bin/env perl
use strict;
use warnings;
use 5.016;

for (<DATA>) {
    chomp;
    print "Match: $_\n" if /(?=name=bob)(?!flags=.*?cat.*?;)/;
}

__DATA__
name=bob;flags=human;age=10
name=tiddles;flags=cat,black;age=3
name=bob;flags=cat,white;age=6

[download]

My understanding is that this matches if name is set to 'bob' and flags do not contain 'cat' (searching up to the first semicolon). However, it returns both 'bob' lines.

Am I missing something obvious here? I understand that lookaheads are zero-width matches, but maybe this is something to do with anchoring?

PS: I know this could probably be done simpler by splitting on ';' into a hash and validating the hash, but this is a learning exercise :)

Many thanks

In reply to Multiple regexs into single combined regex using lookaheads by mxb

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