Recapping the test command

So far, we have used the built-in test command to drive our conditional statements. Using other options with test, we can look at the returned value to determine the status of files in the filesystem. Running the test command without any options will return a false output:

$ test

Testing files

Commonly, we can use test to check the conditions based around files. For example, to test whether a file is present or not, we can use the -e option. The following command will test the existence of the /etc/hosts file:

test -e /etc/hosts

We can run this test again, but this time check that the file not only exists but is a regular file as opposed to having some special purpose. Specific file types can be directories, pipes, and links, among others. The option for a regular file is -f:

$ test -f /etc/hosts

Adding logic

If we need to open a file from within our script, we test that the file is both a regular file and has the read permission set. To achieve this with test, we can...