Using set -e / set +e in bash with functions

Question

I've been using a simple bash preamble like this in my scripts:

#!/bin/bash
set -e

In conjunction with modularity / using functions this has bitten me today.

So, say I have a function somewhere like

foo() {
  #edit: some error happens that make me want to exit the function and signal that to the caller 
  return 2
}

Ideally I'd like to be able to use multiple small files, include their functions in other files and then call these functions like

set +e
foo
rc=$?
set -e

. This works for exactly two layers of routines. But if foo is also calling subroutines like that, the last setting before the return will be set -e, which will make the script exit on the return - I cannot override this in the calling function. So, what I had to do is

foo() {
  #calling bar() in a shielded way like above
  #..      

  set +e
  return 2
}

Which I find very counterintuitive (and also not what I want - what if in some contexts I'd like to use the function without shielding against failures, while in other contexts I want to handle the cleanup?) What's the best way to handle this? Btw. I'm doing this on OSX, I haven't tested whether this behaviour is different on Linux.

Answer 1

Shell functions don't really have "return values", just exit codes.

You could add && : to the caller, this makes the command "tested", and won't exit it:

foo() {
    echo 'x'
    return 42
}

out=$(foo && :)
echo $out

The : is the "null command" (ie. it doesn't do anything). In this case it doesn't even get executed, since it only gets run if foo return 0 (which it doesn't).

This outputs:

x

It's arguably a bit ugly, but then again, all of shell scripting is arguably a bit ugly ;-)

Quoting sh(1) from FreeBSD, which explains this better than bash's man page:

 -e errexit
         Exit immediately if any untested command fails in non-interactive
         mode.  The exit status of a command is considered to be explicitly
         tested if the command is part of the list used to control an if,
         elif, while, or until; if the command is the left hand operand of
         an “&&” or “||” operator; or if the command is a pipeline preceded
         by the ! operator.  If a shell function is executed and its exit
         status is explicitly tested, all commands of the function are con‐
         sidered to be tested as well.