$ perl -wle '{ package Foo; sub import { *{caller."::readpipe"}
  = sub {"Foo"} } } BEGIN { Foo->import() } print `xyz`'
Foo

$ perl -wle 'sub import { *{caller."::readpipe"} = sub {"Foo"} }
  BEGIN { main->import() } print `xyz`'
Can't exec "xyz": No such file or directory at -e line 2.