sub do_somn {
    my $self = shift;
    for my $username ($self->{username}) {
        my $a = $username;
        my $b = $username;
        # ...
    }
}

##</code><code>##

/x/ and $_ .= "y" for $self->{option};

##</code><code>##

$self->{option} .= "y" if $self->{option} =~ /x/;