The "hash" solution is probably the fastest, but less flexible as you can only check on the exact match between IDs and the filename part of the filepath.

It will not work if you have to check if the ID is *somewhere* mentioned in the filepath.

Still you do not have to despair! Nor do you have to check each filepath against each ID with a separate regex (which would be very slow).

Through the magic of Regexp::Assemble it only takes a program of a few lines:

use Modern::Perl;
use Regexp::Assemble;
use autodie;

open my $PATTERNS, '<', './patterns.txt';
my $re_pattern = Regexp::Assemble->new->add(<$PATTERNS>)->re;
close $PATTERNS;

open my $PATHS, '<', './paths.txt';
do {print unless /$re_pattern/} while <$PATHS>;
close $PATHS;
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