Mastering Linux Shell Scripting - Second Edition

Testing strings

We can test for the equality or inequality of two strings. For example, one of the ways to test the root user is using the following command:

test $USER = root  

We could also write this using the square bracket notation:

[ $USER = root ]  

Note that you must put a space between each bracket and the inner testing condition as previously shown.

Equally, we could test for a non-root account with the following two methods:

test ! $USER = root
[ ! $USER = root ] 

We can also test for the zero values or non-zero values of strings. We saw this in an earlier example in this chapter.

To test if a string has a value, we can use the -n option. We can check to see if the current connection is made through SSH by checking for the existence ...