You seem to be referring to accessing and changing global variables from inside a subroutine. But notice that Anonymous Monk's example doesn't use global variables. It uses the the fact that perl actually uses call-by-reference when calling a subroutine. The variable @_ contains references to the variables that were used in the subroutine invocation. That is why it is so important to use something like my ($bla,$x,@f)= @_; in subroutines. Because otherwise you are in danger of changing values at a distance.