...must...resist...urge...to...post...symbolic...reference...example...

Whew! I wrote the symbolic reference example, but didn't post it. Here are a couple alternatives:

You can use brute force:

while (my $inp = <>) {
    $inp =~ s/^\s*(\w+)\s*$/$1/;
    if    ($inp eq 'AB') { AB() }
    elsif ($inp eq 'CD') { CD() }
    ... etc ...    
    else {
        print "Command unknown: '$inp'\n";
    }
}
[download]

If you're using a more modern perl the brute force method could look like:

while (my $inp = <>) {
    $inp =~ s/^\s*(\w+)\s*$/$1/;
    given ($inp) {
       when ('AB') { AB() }
       when ('CD') { CD() }
       ... etc ...
       default {
        print "Command unknown: '$inp'\n";
    }
}
[download]

However, a better method is a dispatch table. There's a little more setup work at the beginning, but as you add new command handlers, you'll find it's easier to maintain:

my %dispatch_table = (
    AB => \&AB,
    CD => \&CD,
    ... etc ...
);
while (my $inp = <>) {
    $inp =~ s/^\s*(\w+)\s*$/$1/;
    if (exists $dispatch_table{$inp}) {
        &{$dispatch_table{$inp}}();
    }
    else {
        print "Command unknown: '$inp'\n";
    }
}
[download]

...roboticus

When your only tool is a hammer, all problems look like your thumb.