04.the-problem.rst

set -o errexit considered harmful

The problem

call tree in 02.errexit-broken.sh:

01  +  main
    |
02  +-- echo "main: entering"
    |
03  +-- if authenticate
    |   # now part of an `if` keyword. Effectivelly forcing all the
    |   # code called by `authenticate` run with `set +e`
    |
04  +------ test `prompt_user` = "Alice"
    |       # contrary to common sense, this *still* is
    |       # part of the `if` keyword
    |
05  +-- then
    |
06  +-- echo "lanuching missiles"
    |
07  +-- fi

Therefore using errexit can easily result into Action at distance [4] anti-pattern.

[1]	Posix issue tracker http://austingroupbugs.net/view.php?id=537

[2]	why does errexit exist in its current utterly useless form? http://lists.gnu.org/archive/html/bug-bash/2012-12/msg00093.html

[3]	Some poor fellow on Stack Overflow http://stackoverflow.com/questions/13870291/trouble-with-errexit-in-bash

[4]	http://en.wikipedia.org/wiki/Action_at_a_distance_(computer_programming)