#!/usr/bin/perl -w
use strict;

my $m= 'aeiou';
my @m= qw( a e i o u );
my $at= 'tye@perlmonks';
my $dollar= 'tye$perlmons';
sub Try {
    local( $" )= ",";
    print "(@_)\n";
}
Try $at =~ /[@m]+/g;
Try $at =~ /[m@]+/g;
Try $dollar =~ /[$m]+/g;
Try $dollar =~ /[m$]+/g;
__END__
Outputs:
(e,e,o)
(@,m)
(e,e,o)
/[m5.006+/: unmatched [] in regexp at reinterp.pl line 12.