Bash : automatically exit the script if a command fails

"set -e, an alias of set -o errexit, is used to exit the script everytime a command fails. By putting this command at the top of your script, you can avoid to manually test all the return codes.

Automatically test if a command fails
#!/bin/bash

# Exit for a return code not 0
set -e;
true;

# Do not exit for a return code not 0
# until the next set -e
set +e;

false;
echo 'This false does not exit the script';

false;
if [ $? -ne 0 ]; then
    echo 'That\'s how we can manually check that the return code is not 0';
fi


# Put back the automatic exit
set -e;

false || { echo "Custom error message"; }

echo 'Still in the script because the return code of false || echo ... is 0';

false;
echo 'Will never be displayed because the previous command exited the script';

Result of this script
$ ./script.sh
This false does not exit the script
That's how we can manually check that the return code is not 0
Custom error message
Still in the script because the return code of false || echo ... is 0

Another use of set for testing if a variable is initialized.