Debugging

Tracing

-x in Command Line

$ /bin/bash -x my_script.sh

-x in Script

#!/bin/bash -x
...

Turn on/off tracing with set

#!/bin/bash
number=1
set -x # Turn on tracing
if [ $number = 1 ]; then
 echo "Number is equal to 1."
else
 echo "Number is not equal to 1."
fi
set +x # Turn off tracing

Change PS4

$ export PS4='$LINENO + '
$ ./trouble.sh
5 + number=1
7 + '[' 1 = 1 ']'
8 + echo 'Number is equal to 1.'
Number is equal to 1.