I usually don't write bash scripts. If use the terminal often to run AWS ClI commands, but if I need logic or something a bit more complex I'd rather go for a tiny NodeJs file.

It feels more natural to me, more readable and I can debug what is going wrong.

Sometimes though I have to touch old bash scripts used for continuous integration. Like today. Well, it was actually a YAML file used to run GilabCI Pipelines, but the job script contained a bash script, that wasn't working.

if [$CI_PIPELINE_SOURCE == "schedule"] && [[ -z "$STAGE" ]]; then
 # collapsed multi-line command

This condition was giving an error, which was swallowed by the CI giving a successful job, but with an, of course, unexpected behavior.

27/bin/bash: line 118: [schedule: command not found

I remembered that there was something about Single Brackets or double Brackets so I immediately changed that to

[[$CI_PIPELINE_SOURCE == "schedule"]]

Nope.

Then I remembered there was something about Wrapping Variables in Quotes therefore I changed to

[["$CI_PIPELINE_SOURCE" == "schedule"]]

Nope.

I checked the docs and Stackoverflow
After googling and trying to mix and match, Single Equal / Single Equals / Quotes in every possible allowed combination I was left staring at the script and at the StackOverflow example for a while. Until it struck me.

The space.

T h e f r e a k i n g m i s s i n g s p a c e

if [[ $CI_PIPELINE_SOURCE  == "schedule" ]] && [[ -z "$STAGE" ]]; then

I just repropose here the Stackoverflow explanation as my own reminder

= || == ?

Bash allows == to be used for equality with [ (but this is not standard)

To quote or not to quote?

Always wrap your variables with quotes, because if it is empty, your Bash script would encounter a syntax error. (Not because it would try to compare something with a null value, but because the syntax itself would be kind of broken.)

Hope it helps.