# or even:
$scalar =~ /[^1-5]/ ? &is_bad : &is_good;
print $scalar =~ /[^1-5]/ ? "bad" : "OK!";
$scalar !~ /[^1-5]/ && print "OK!";
print "OK!" unless $scalar =~ /[^1-5]/;
print "OK!" if $scalar !~ /[^1-5]/;