Learning Perl, Second Edition

1.4. Basic Concepts

A shell script is nothing more than a sequence of shell commands stuffed into a text file. The file is then "made executable" by turning on the execute bit (via chmod +x filename) and then the name of the file is typed at a shell prompt. Bingo, one shell program. For example, a script to run the date command followed by the who command can be created and executed like this:

% echo date >somescript
% echo who >>somescript
% cat somescript
date
who
% chmod +x somescript
% somescript
[output of date followed by who]
%

Similarly, a Perl program is a bunch of Perl statements and definitions thrown into a file. You then turn on the execute bit^[2] and type the name of the file at a shell prompt. However, the file has to indicate that this is a Perl program and not a shell program, so you need an additional step.

^[2] On UNIX systems, that is. For directions on how to render your scripts executable on non-UNIX systems, see the Perl FAQ or your port's release notes.

Most of the time, this step involves placing the line

#!/usr/bin/perl

as the first line of the file. But if your Perl is stuck in some nonstandard place, or your system doesn't understand the #! line, you'll have a little more work to do. Check with your Perl installer about this. The examples in this book assume that you use this common mechanism.

Perl is mostly a free-format language like C—whitespace between tokens (elements of the program, like print or +) is optional, unless two tokens put together can ...