print "my_sub ", test_for_sub("my_sub") ? "exists\n" : "doesn't exist\n";
print "no_sub ", test_for_sub("no_sub") ? "exists\n" : "doesn't exist\n";

sub test_for_sub {
        my ($expr) = @_;
        return eval "defined &$expr";
}

sub my_sub { 1; }