Perl uses the following environment variables:
Used if chdir has no argument.
Used if chdir has no argument and HOME is not set.
Used in executing subprocesses, and in finding the Perl script if -S is used.
A colon-separated list of directories to look in for Perl library files before looking in the standard library and the current directory.
The command to get the debugger code. Defaults to BEGIN { require 'perl5db.pl' }.
Used instead of PERL5LIB if the latter is not defined.