Bash debugging

We have one more trick up our sleeve to prove that values are expanded properly: running the Bash script with debug logging. Look at the following execution:

reader@ubuntu:~/scripts/chapter_09$ bash -x test-shorthand-variable.sh 
+ DIRECTORY=/tmp/
+ test -d /tmp/
+ test_rc=0
+ '[' -d /tmp/ ']'
+ simple_rc=0
+ [[ -d /tmp/ ]]
+ extended_rc=0
+ echo 'The return codes are: 0, 0, 0.'
The return codes are: 0, 0, 0.

If you compare this to the actual script, you will see that the script text test -d ${DIRECTORY} is resolved to test -d /tmp/ at runtime. This is because, instead of running bash test-shorthand-variable.sh, we're running bash -x test-shorthand-variable.sh. In this case, the -x flag tells Bash to print commands and their arguments as they are executed—a very handy thing to remember if you're ever building scripts and unsure why the script is not doing what you expect it to do!