I have a shell script with the following line in it:
[ "$DEBUG" == 'true' ] && set -x
set -x
enables a mode of the shell where all executed commands are printed to the terminal. In your case it's clearly used for debugging, which is a typical use case for set -x
: printing every command as it is executed may help you to visualize the control flow of the script if it is not functioning as expected.
set +x
disables it.