How to catch and handle nonzero exit status within a Bash function?

Question

Say I have the following (pointless) Bash function:

myfunc() {
    ls
    failfailfail
    uptime
}

I run it as follows:

myfunc || echo "Something is wrong."

What I want to happen is ls runs (as it should), failfailfail does not work (since it doesn't exist), and uptime doesn't run. The return value of the function would be nonzero, and the error message would be shown. The return value doesn't have to be the exact exit status of the failed command, it just shouldn't be zero.

What actually happens is I get the output of ls, followed by "-bash: failfailfail: command not found", followed by the output of uptime. The error message is not shown, because the failed exit status is getting eaten.

set -e has no useful effect, either within the function or in the scope where the function is called. The only way I can get this to work the way I want is:

myfunc() {
    ls || return $?
    failfailfail || return $?
    uptime || return $?
}

But this seems awfully repetitive and ugly. Is there another way to clean this up?

score 3 · Answer 1 · answered Apr 29 '16 at 00:19

Under set -e, the non-existence of failfailfail causes the whole script to exit (or the subshell, if the function is executed in a subshell).

If you don't need to modify the shell state from the function, you can run it in a subshell.

myfunc() (
    set -e
    ls
    failfailfail
    uptime
)

Another approach in bash is to set an ERR trap to execute return. If you want to make it a local setting, you need to restore the old trap value, which is a little cumbersome.

myfunc() {
    local old_ERR_trap=$(trap -p ERR)
    if [[ -z $old_ERR_trap ]]; then old_ERR_trap="trap - ERR"; fi
    trap 'local ret=$?; eval "$old_ERR_trap"; return $ret' ERR
    ls
    failfailfail
    uptime
}

score 0 · Answer 2 · answered Apr 28 '16 at 16:27

0

The only way you can make it simpler is by combining it all in one command but it makes the script a bit harder to maintain than your last version:

myfunc() {
    ls && failfailfail && uptime || return $?
}

answered Apr 28 '16 at 16:27

Julie Pelletier

7,622

1

You can put line breaks after &&, which would make this easier to maintain IMO. You don't need backslashes for that, either. – Wildcard Apr 28 '16 at 16:31

score 0 · Answer 3 · answered Apr 28 '16 at 16:34

0

Given that they are all simple commands, you could do it something like the following:

myfunc() {
  ls &&
  failfailfail &&
  uptime ||
  return $?
}

answered Apr 28 '16 at 16:34

Wildcard

36,499

It's interesting but I think it may cause more confusion that way. – Julie Pelletier Apr 28 '16 at 16:35
Instead of posting a new answer, you should edit the existing one. Your answer doesn't need to be a separate answer from the previous one. – MAChitgarha Sep 06 '19 at 12:22
@MAChitgarha this is from three years ago. – Wildcard Sep 06 '19 at 15:35
@Wildcard I know, but some people may search for a solution, now. Editing the previous answer is more helpful than adding an answer, though. – MAChitgarha Sep 07 '19 at 11:42

score 0 · Answer 4 · answered Apr 29 '16 at 18:17

0

Sometimes things are better put in a Makefile, which handles this sort of thing.

#!/bin/bash
myfunc() { # watch out for tabs!
        make -f - <<!
default:
        ls -d
        failfailfail
        uptime
!
}

answered Apr 29 '16 at 18:17

meuh

51,383

This feels... devious. – smitelli May 02 '16 at 20:04

How to catch and handle nonzero exit status within a Bash function?

4 Answers4