Programming Perl, 3rd Edition

Chapter 19. The Command-Line Interface

This chapter is about aiming Perl in the right direction before you fire it off. There are various ways to aim Perl, but the two primary ways are through switches on the command line and through environment variables. Switches are the more immediate and precise way to aim a particular command. Environment variables are more often used to set general policy.

Command Processing

It is fortunate that Perl grew up in the Unix world, because that means its invocation syntax works pretty well under the command interpreters of other operating systems, too. Most command interpreters know how to deal with a list of words as arguments and don't care if an argument starts with a minus sign. There are, of course, some sticky spots where you'll get fouled up if you move from one system to another. You can't use single quotes under MS-DOS as you do under Unix, for instance. And on systems like VMS, some wrapper code has to jump through hoops to emulate Unix I/O redirection. Wildcard interpretation is a wildcard. Once you get past those issues, however, Perl treats its switches and arguments much the same on any operating system.

Even when you don't have a command interpreter per se, it's easy to execute a Perl program from another program written in any language. Not only can the calling program pass arguments in the ordinary way, it can also pass information via environment variables and, if your operating system supports them, inherited file descriptors ...