Use File::Basename

This core module has been shipped with perl since version 5. As its
behavior is equivalent to the regex versions deleted, we may as well use
it as it is one less thing for me to maintain.
Add shell-specific env command

The env command now spits out environment modification commands specific
to the shell specified as an argument, or the environment variable
$SHELL otherwise. Unknown shells will get POSIX output.
Switch bug contact email

toast-bugs@toastball.net --> toast-bugs@llama.is