Debugging / Tracing bash shell scripts

Source: http://www.linuxcommand.org/wss0100.php

Watching your script run

It is possible to have bash show you what it is doing when you run your script. To do this, add a "-x" to the first line of your script, like this:

#!/bin/bash -x
       

Now, when you run your script, bash will display each line (with substitutions performed) as it executes it. This technique is called tracing. Here is what it looks like:

[me@linuxbox me]$ ./trouble.bash
+ number=1
+ '[' 1 = 1 ']'
+ echo 'Number equals 1'
Number equals 1

Alternately, you can use the set command within your script to turn tracing on and off. Use set -x to turn tracing on and set +x to turn tracing off. For example.:

#!/bin/bash

number=1

set -x
if [ $number = "1" ]; then
    echo "Number equals 1"
else
    echo "Number does not equal 1"
fi
set +x