Using the test shell builtin

It is probably time for us to pull over to the side of the scripting highway and look a little more at this command test. This is both a shell builtin and a file executable in its own right. Of course, we will have to hit the built-in command first, unless we specify the full path to the file.

When the test command is run without any expressions to evaluate, then the test will return false. So, if we run the test as shown in the following command:

$ test

The exit status will be 1, even though no error output is shown. The test command will always return either True or False or 0 or 1, respectively. The basic syntax of test is:

test EXPRESSION

Or, we can inverse the test command with:

test ! EXPRESSION

If we need to include multiple expressions, these can be AND or OR together using the -a and -o options, respectively:

test EXPRESSION -a EXPRESSION
test EXPRESSION -o EXPRESSION

We can also write in a shorthand version replacing the test with square brackets to surround...