Apart from using can (which is a great way), you can also do:

package A;

sub b {
    print "called A::b\n";
}

package main;

my $pack='A';
{
 no strict 'refs';
 &{"${pack}::b"}();
}
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That is, creating a soft-ref to the sub on-the-fly.

-- 
        dakkar - Mobilis in mobile