In reply to daxim, I concur with you that code excerpts would assist the respondent to be certain that he had given a definitive answer.

I considered doing that against a descriptive approach and sided with the latter because I anticipated that the "show all code" approach might have put off more people than it attracted. But I take your valuable feedback on-board, and thanks again for your time and advice.

In response to tobyink - thank you so much. You've probably seen this before, or you're very "switched on" as you appear to have understood the problem immediately and described the solution clearly and explicitly.

I made the following changes to common.pm and the problem is resolved :

package common;
use Exporter 'import';
our @EXPORT=qw( doit basename );

Many thanks again to both of you,
Peter.