Mastering Linux Shell Scripting - Second Edition

Square brackets as not seen before

As an alternative to the test command, we can implement the same conditional tests using the single square bracket. Repeating the previous conditional test and omitting the command itself. We will rewrite this, as shown in the following command:

 $ [ -f /etc/hosts -a -r /etc/hosts ]

Many times, even as experienced administrators, we are used to language elements and we accept them as they are. I feel many Linux administrators will be surprised to learn that [ is a command for both a shell built-in and a standalone file. Using the type command, we can verify this:

$ type -a [

We can see the output of this command in the following screenshot confirming its existence:

The built-in [ command imitates the