Specifications

Instead of entering commands and waiting for their

responses, you can compose scripts that are run without

direct interaction.

This chapter discusses some basics of shell scripting on Mac OS X, including

automation and scheduling, as well as a brief overview of what a shell script is.

It does not provide information on writing shell scripts in general.

For information about how to write shell scripts, see the Shell Scripting Primer on

the Apple Developer Connection website.

What is a Shell Script?

A shell script is a text le that contains one or more UNIX commands. You run a shell

script to perform commands you might otherwise run interactively at the command line.

Shell scripts are useful because you can combine many common tasks into one script,

saving you time and possible errors when running similar tasks over and over. They

can also be easily automated using tools such as launchd or Apple Remote Desktop.

A shell script begins with a character combination that identies it as a shell script, the

characters ‘#’ and ‘!’ (together called a “shebang”) followed by a reference to the specic

shell that the script should be run with. For example, here’s the rst line of a shell script

that would be run with sh:

#!/bin/sh

You should document your shell scripts with comments. To make a comment, start

the line with the number sign (#). Every line of a comment needs to begin with the

number sign:

#This program returns the

#contents of my Home folder

You can put blank lines in a shell script to help visually distinguish dierent sections

of the script.

Scripting the Command Line