How to run a command before a Bash script exits?

Question

Here's an example of using trap:

#!/bin/bash -e

function cleanup {
  echo "Removing /tmp/foo"
  rm  -r /tmp/foo
}

trap cleanup EXIT
mkdir /tmp/foo
asdffdsa #Fails

Output:

dbrown@luxury:~ $ sh traptest
t: line 9: asdffdsa: command not found
Removing /tmp/foo
dbrown@luxury:~ $

Notice that even though the asdffdsa line failed, the cleanup still was executed.

From the bash manpage (concerning builtins):

trap [-lp] [[arg] sigspec ...]
The command arg is to be read and executed when the shell receives signal(s) sigspec.

So, as indicated in Anon.'s answer, call trap early in the script to set up the handler you desire on ERR.

From the reference for set:

-e

Exit immediately if a simple command (see section 3.2.1 Simple Commands) exits with a non-zero status, unless the command that fails is part of an until or while loop, part of an if statement, part of a && or || list, or if the command's return status is being inverted using !. A trap on ERR, if set, is executed before the shell exits.

(Emphasis mine).

sh version of devguydavid's answer.

#!/bin/sh
set -e
cleanup() {
  echo "Removing /tmp/foo"
  rm  -r /tmp/foo
}
trap cleanup EXIT
mkdir /tmp/foo
asdffdsa #Fails

ref: shellscript.sh