Debugging shell scripts

Sometimes you might need to debug or see what is really running in your shell script. If you want to see each line/command executed simply add "-x" to your first line where you define your shell/interpreter. This will output every executed command with a "+" before the line.

#! /bin/sh -x
echo "Hello World!"

This will output :

+echo "Hello World!"
Hello World!

I know this works with sh and bash, but I do not know the other shells.

Also debugging especially long shell scripts can be a hard job. If you set the "-x" option at the beginning of the script, then it will output all the commands executed.
For this purpose, you can add "set -x" before the place you want to debug and "set +x" at the end.

#! /bin/sh
echo "This is the test"
set -x
echo "Only show this part"
set +x

This will output:

This is the test
+echo "Only show this part"
+set +x
Only show this part


Also if you want to run your script, but not execute the commands you can use the -n option. This is best for checking your syntax.
Happy debugging with your favorite shell.