my ($called_name) = $0 =~ m#/([^/]+)$#;

{
     no strict;

     &{"mode_$called_name"}() if (defined &{"mode_$called_name"});
}

sub mode_foo
{
     # If program is called as "foo"
}
sub mode_moo
{
     # If program is called as "moo"
}