Last Updated: 2024-11-21

I wanted to write a health check script that always returned a predictable exit code (the number 1) if a HTTP service was down. This predictability was to replace getting (e.g.) 10 possible exit codes depending on the exact reason the curl command failed.

The code ended up as the following

curl --fail localhost:8000 || exit 1

How does this work?

• Exit codes: If curl was successful (i.e. the site was live), it would return 0. Otherwise it could return a variety of exit codes depending on the nature of the error.
• the || operator gives the first "truthy" item it encounters
• when curl returns 0, this counts as "truthy". This might trip you up, as most other languages do things the other way around, making 1 truthy and 0 falsey.
• when curl returns non-zero, it is also falsey, so the part after the double pipe is run (exit 1), giving us the predictability.