An effective solution doesn't necessarily mean Perl in this case.

PATH is most likely set, assuming you're using bash by the file .bash_profile for login shells or by .bashrc for non-login shells in your home directory.

By the description I was assuming that you were interested in setting the PATH for your shell use.

From perldoc perlvar: "$ENV{expr} - The hash %ENV contains your current environment. Setting a value in "ENV" changes the environment for any child processes you subsequently fork() off."

This means a script cannot modify the ENV for it's parent shell, only for it's children processes. A shell is a script's parent process.