proper way to detect shell exit code when errexit

Question

I prefer to write solid shell code, so the errexit & nounset is alway set.

The following code will stop at bad_command line

#!/bin/bash
set -o errexit ; set -o nounset
bad_command # stop here
good_command

I want to capture it, here is my method

#!/bin/bash
set -o errexit ; set -o nounset
rc=1
bad_command && rc=0 # stop here
[ $rc -ne 0 ] && do_err_handle
good_command

Is there any better or cleaner method

My Answer:

#!/bin/bash
set -o errexit ; set -o nounset
if ! bad_command ; then
  # error handle here
fi
good_command

Answer 1

I cobbled together a (hopefully) textbook example from all the answers:

#!/usr/bin/env bash

# exit immediately on error
set -o errexit

file='dfkjlfdlkj'
# Turn off 'exit immediately on error' during the command substitution
blah=$(set +o errexit && ls $file) && rc=$? || rc=$?
echo $blah
# Do something special if $rc
(( $rc )) && echo failure && exit 1
echo success

Answer 2

Keep with errexit. It can help find bugs that otherwise might have unpredictable (and hard to detect) results.

#!/bin/bash
set -o errexit ; set -o nounset

bad_command || do_err_handle
good_command

The above will work fine. errexit only requires that the line pass, as you do with the bad_command && rc=0. Therefore, the above with the 'or' will only run do_err_handle if bad_command fails and, as long as do_err_handle doesn't also 'fail', then the script will continue.

Answer 3

In bash you can use the trap builtin which is quite nice. See https://unix.stackexchange.com/questions/79648/how-to-trigger-error-using-trap-command

Not sure how portable it is with other shells.. so YMMV

Answer 4

Agree with comments, so if you can give up errexit then you can easily shorten your code to

 bad_command || do_err_handle
 good_command

I hope this helps.

Answer 5

what if you want to know exit status of bad_command?

I think the simplest way is to disable errexit:

#!/bin/sh
set -o errexit

some_code_here

set +o errexit
bad_command
status=$?
set -o errexit
process $status