Linux System Administration

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Chapter 10: Scripting

variable is the name of the script itself. The $* variable contains all the arguments as

one string value. These variables can then be passed along to commands the script

runs:

admin@server1:~$ cat files

#!/bin/bash

ls -Alv $*

admin@server1:~$ ./files hello hello2 today

-rwxr-xr-x 1 admin admin 48 2006-07-25 13:25 hello

-rwxr-xr-x 1 admin admin 51 2006-07-25 14:45 hello2

-rwxr-xr-x 1 admin admin 45 2006-07-25 14:49 today

admin@server1:~$

The special variable $$ contains the current process’s process ID. This can be used to

create a unique temporary filename. If multiple copies of the same script are running

at the same time, each will have a different process ID and thus a different tempo-

rary filename.

Another useful variable is

$?, which contains the return status of the most recent

command executed. We’ll use this later in this chapter to check for the success or

failure of program execution in a script.

Useful Elements for bash Scripts

We’ve introduced the basic elements of bash that you’ll use in the everyday running

of interactive commands. Now let’s look at some things that will help you write

effective scripts.

Expressions

bash expressions contain variables and operators such as == (equals) and > (greater

than). These are usually used in tests, which can be specified in several ways:

test $file == "test"

[ $file == "test" ]

[[ $file == "test" ]]

If you use the test command, ...