How to Debug a Bash script?

How to debug a Bash script if it has some bugs? Common techniques like printing varibles out for checking apply for bash too. For bash, I also use 2 bash-specific techniques.

Use errexit option

Run the script with -e option like bash -e your-script.sh or add set -o errexit to the beginning of the script.

errexit makes bash exit immediately if one statement’s return code is not 0. This way, you know which statement goes wrong.

Use xtrace option

Run the script with -x option like bash -x your-script.sh or add set -o xtrace to the beginning of the script.

The -x option will make bash print statements executed so that you know what is going on.

One example

For example,

#!/bin/bash

set -x

i=0
let i=i+1

echo $i
false # this will stop the script run with -e
date

The execution of that script with bash -e script.sh will print

+ i=0
+ let i=i+1
+ echo 1
1
+ false

By combining the 2 techniques together, which statement/step went wrong is printed out on the STDOUT.