Thank you very much for the detailed explanation haukex. It is very complete. To answer some of your other questions I am referring to 2nd Edition (1999) of Camel book. The example on p.76 is in the explanation of tr, not in the explanation of eval. the literal text from that page is :  eval "tr/$oldlist/$newlist/"; die $@ if $@; I knew that perl had progressed some since 1999 but it did not occur to me that there would of course be further editions of the Camel book. Thanks again. pgmer6809