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 script if -S is used.

A colon-separated list of directories in which to look for Perl library files before looking in the standard library and the current directory.

The command used to get the debugger code. If unset, uses
	require 'perldb.pl'

Apart from these, perl uses no other environment variables, except to make them available to the script being executed, and to child processes. However, scripts running setuid would do well to execute the following lines before doing anything else, just to keep people honest:

    $ENV{'PATH'} = '/bin:/usr/bin';    # or whatever you need
    $ENV{'SHELL'} = '/bin/sh' if $ENV{'SHELL'} ne '';
    $ENV{'IFS'} = '' if $ENV{'IFS'} ne '';