Failing fast in bash scripts

If you want your bash script to stop execution as soon as any of the commands returns a non-zero exit status, invoke bash with the -e option.

For example, the following script will continue to run, even though the sub-shell exited with the status 1.

#!/bin/bash 
( exit 1 ) # subshell that returns non-zero exit status
echo "This will be echoed"

However, if the script invokes bash with the -e option, the script ends as soon as the subshell returns 1.

#!/bin/bash -e
( exit 1 ) # subshell that returns non-zero exit status
echo "This will not be echoed"

Note: Although I’ve used the subshell as an example here, but the script will stop executing for any command failure e.g. wget, curl, etc.

Another way to enable bash scripts to stop execution on failure is by using the set -e option. This can be set at any point in the script.

#!/bin/bash
( exit 1 ) # subshell that returns non-zero exit status
echo "This will be echoed"
set -e # enable fail fast mode
( exit 1 ) # script will not execute beyond this
echo "This will NOT be echoed"

Lastly, the fail fast mode can be disabled by using set +e in the script.

#!/bin/bash
( exit 1 )
echo "This will be echoed"
set -e # enable fail fast mode
echo "Just echoing something"
set +e # disable fail fast mode
( exit 1 )
echo "This will STILL be echoed"