local and do

'local modifies the listed variables to be local to the enclosing block, file, or eval' - but

• a do is only 'largely' like an eval - this is one of the respects in which it differs
• the script that you do may be physically in another file, but when you do it, it is as if it is part of the file where the do is

Or to put it more succinctly, if a.pl uses a filehandle FH, and so does b.pl, and you do b.pl from a.pl, you cannot use local(*FH) in b.pl to stop b.pl's FH from being the same handle as a.pl's.

I worked round this by putting a package X at the top of b.pl, no doubt there are other ways.