> Why doesn't set -e (or set -o errexit, or trap ERR) do what I expected?
> set -e was an attempt to add "automatic error detection" to the shell. Its goal was to cause the shell to abort any time an error occurred, so you don't have to put || exit 1 after each important command. That goal is non-trivial, because many commands intentionally return non-zero.
> What are the advantages and disadvantages of using set -u (or set -o nounset)?
> Bash (like all other Bourne shell derivatives) has a feature activated by the command set -u (or set -o nounset). When this feature is in effect, any command which attempts to expand an unset variable will cause a fatal error (the shell immediately exits, unless it is interactive).
pipefail is not quite as bad, but is nevertheless incompatible with most other shells.
is a good example of why -e and pipefail are dangerous. grep will return an error status if it gets an error (e.g. file not found) or if it simply fails to find any matches. With -e and pipefail, this command will terminate the script if there happen to be no matches, so you have to use something like || true at the end... which completely breaks the exit-on-error behavior that was the point of the exercise.
> GreyCat's personal recommendation is simple: don't use set -e. Add your own error checking instead.
> rking's personal recommendation is to go ahead and use set -e, but beware of possible gotchas. It has useful semantics, so to exclude it from the toolbox is to give into FUD.
> Why doesn't set -e (or set -o errexit, or trap ERR) do what I expected?
> set -e was an attempt to add "automatic error detection" to the shell. Its goal was to cause the shell to abort any time an error occurred, so you don't have to put || exit 1 after each important command. That goal is non-trivial, because many commands intentionally return non-zero.
http://mywiki.wooledge.org/BashFAQ/112:
> What are the advantages and disadvantages of using set -u (or set -o nounset)?
> Bash (like all other Bourne shell derivatives) has a feature activated by the command set -u (or set -o nounset). When this feature is in effect, any command which attempts to expand an unset variable will cause a fatal error (the shell immediately exits, unless it is interactive).
pipefail is not quite as bad, but is nevertheless incompatible with most other shells.