my $chars = q{abcde};           # Specify the characters.
my $matchset = "[$chars]";      # Set up a character class.
my $reg_match = qr{$matchset};  # Turn it into a regexp.
my @strings = qw/ apple logs frog elmo /;
foreach my $string ( @strings ) {
    print "$_ matched\n" if $string =~ $reg_match;
}
__END__
apple
elmo