ex: 
A1 changed to A2
A2 changed to A1

Thanks

$m = "A1";
or
$m = "A2";

This wont work:
$m =~ tr(/1/2/ | /2/1/);

This works, but I dont like it:

if ($m =~ /1/){
     $machine =~ s/1/2/g;
}
else{
     $m =~ s/2/1/g;
}