Performing Tests

There will be times when your scripts will need to test for a certain condition before making a decision on which action to take. You might need to check for the existence of a certain file or directory, whether certain permissions are set on a file or directory, or for a myriad of other things. There are three ways to perform a test, which are:

• Use the keyword test followed by a test condition, with another command joined to it with either a && or a || construct.
• Enclose the test condition within a set of square brackets.
• Use an if. . .then construct

Let’s start by looking at the test keyword.

Using the test Keyword

For our first example, let’s test to see whether a certain directory exists, and then create it if it doesn’t. Here’s how that works:

[donnie@fedora ~]$ test -d graphics || mkdir graphics
[donnie@fedora ~]$ ls -ld graphics/
drwxr-xr-x. 1 donnie donnie 0 Sep 26 15:41 graphics...