Bash set builtin

Shell scripts I come across sometimes have for instance “#!/bin/bash -eux” on the first line. Because I’ve Googled for this too many times now, I’ll record the meaning of these options here for my own sanity.

The options (-e, -u and -x) are part of the set builtin. They have the following meaning:

Exit immediately if a pipeline […] returns a non-zero status.
Treat unset variables and parameters […] as an error when performing parameter expansion.
Print a trace of […] commands and their arguments or associated word lists after they are expanded and before they are executed.

For more details and other options, read the manual.