Perl pattern match not working as expected - regex

Question

I'm trying to match values, which may be comma separated, using a regex. Basically, I want to return true if any value in the string does NOT have 3g or 3k starting in the 3rd position.
My test code is as follows:
my #a = ('in3g123456,dh3k123456,dhec110101','dhec110101,dhec123456','in3g123456,dh3k123456', 'c3kasdf', 'usdfusdufs3gsdf' );
foreach (#a) {
print $_;
say $_ =~ /(?:^|,)\w{2}[^(?:3G|3K)]/i ? " true" : " false";
}
This returns
in3g123456,dh3k123456,dhec110101 true
dhec110101,dhec123456 true
in3g123456,dh3k123456 false
c3kasdf false <- whaaaaaaaat?
usdfusdufs3gsdf true
I don't understand why the 4th one is not true. Any help would be appreciated.

Answer 1

[^(?:3G|3K)] reads as "any character but (, ?, etc."
failed
v
c3 kasdf
/(?:^|,)\w{2}[^(?:3G|3K)]/i
Use this:
/(?:^|,)\w{2}(?!3G|3K)/i
Demo: https://regex101.com/r/P2XsgN/1.

Answer 2

How about /\b\w{2}(?!3g|3k)/i.
\b matches the empty string at the beginning or end of a word. Slightly simpler equivalent to (^|,) in this situation.
(?!foo) is a zero-width negative lookahead assertion. So, matches the empty string as long as it's not followed by a substring that matches foo.

Answer 3

You can also split the string first, instead of parsing everything with a regex. That is far more flexible and maintainable, and easier.
When processing the list of the extracted "values" you can match any character twice then your pattern, /^..$patt/. The module List::MoreUtils is useful (and fast) for list manipulations, and its notall function is tailor-made for your condition.
use warnings 'all';
use strict;
use List::MoreUtils qw(notall);
my $file = '...';
open my $fh, '<', $file or die "Can't open $file: $!";
while (<$fh>)
{
my $res = notall { /^..(?:3k|3g)/ } split /,/;
print "$_: " . ($res ? 'true' : 'false'), "\n";
}
I presume that you read from a file. If not, replace while (<$fn>) with for (#strings).
The notall function returns true if any element of the list fails the condition.
The split by default uses $_ so we only need the pattern. Here it is simply , but the pattern takes a regex so one can match separators flexibly. For example, this /[,\s]+/ splits on any amount of , and/or whitespace. So ,, , in a string is matched as a separator, as well as , or space(s).
When applied to the array with your strings the above prints
in3g123456,dh3k123456,dhec110101: true
dhec110101,dhec123456: true
in3g123456,dh3k123456: false
c3kasdf: true
usdfusdufs3gsdf: true

Answer 4

You could use substr to get data at 3rd and 4th position and then compare it with (3g|3k).
substr $_,2,2
#!/usr/bin/perl
use strict;
use warnings;
my #a = ('in3g123456,dh3k123456,dhec110101','dhec110101,dhec123456','in3g123456,dh3k123456', 'c3kasdf', 'usdfusdufs3gsdf' );
foreach (#a) {
my #inputs = split /,/,$_;
my $flag = 0;
foreach (#inputs){
$flag = 1 unless ((substr $_,2,2) =~ /(3g|3k)/);
}
$flag ? print "$_: True\n" : print "$_: False\n";
}
Output:
in3g123456,dh3k123456,dhec110101: True
dhec110101,dhec123456: True
in3g123456,dh3k123456: False
c3kasdf: True
usdfusdufs3gsdf: True
Demo