gistfile1.txt

#!/usr/bin/perl
 
use 5.010;
 
use strict;
use warnings;
 
# ---
 
sub repl {
  my $in = shift;
 
  if ($in eq 'A') { 'foo' }
  elsif ($in eq 'B') { 'bar' }
}
 
my $x = "FARMBUDDY.PEARL.yomama32";
$x =~ s[A|B][repl($&)]eg;
 
say $x;