my %list_of_keys = qw(DNI 1 SNI 1 JRN 1); my $filename = 'foo,JRN,SNI,bar'; my $regex = join('|', map { "\Q$_\E" } keys(%list_of_keys)); $regex = qr{\b($regex)\b}; # case insensitive? while($filename =~ /$regex/ig) { my $key = $1; print "Found key $key\n"; }