This does:

Not really. That only works for the special case where you are performing your sort in main::. It doesn't work if you are in yet another package.

In other words, this fails:

package backwards;
sub pmc { $::b cmp $::a };
package blah;
sub foo { print for sort backwards::pmc ( split /\s+/, `cat $0` ) }
package main;
blah::foo();
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The right way to do it is to prototype your comparator function with ($$) and to use @_ thusly:

package backwards;
sub pmc($$) { $_[1] cmp $_[0] };
package blah;
sub foo { print for sort backwards::pmc ( split /\s+/, `cat $0` ) }
package main;
blah::foo();
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