I'm writing a command line script that will need to be able to be run on a wide variety of machines (Win,Linux,Solaris,Mac etc) whose Perl installations date back around 2 years. I can't upgrade Perl on the machines, nor can I install new modules onto them (various technical reasons). So my question is this: What can my script "assume" has been installed? Is IO::Socket a 'standard module' that comes with every Perl installation and doesn't need additional installing, can Net::SMTP be relied on to "always be there"?. Is there a standard "minimal installation" list of modules etc that I can cross-reference to check my script will run on all possibilities without additional module installation?