bash - 使用 set -e 时如何处理退出代码并获取命令输出

Question

I have set -e at top of script. How to avoid script termination for some commands and process exit code? I have a difficulty in following code sample:
I need both output to variable and exit code, without set -e its easy.

set -e
...
formoutput=$(yad --form --field="Subdomain" --field="Domain" --field="Web master username" \
  --field="Apache group" --field='Webroot' \
  --field='Webroot variables - ${homedir}(of webmaster) ${subdomain} ${webmaster} ${domain}:LBL' \
  --field="Virtualhost ip or domain" \
  --field="Virtualhost port" --field="Server admin email" \
  --field="Create mysql user&db:CHK" \
  --button="Cancel:3" --button="Save defaults:2" --button="Create:0" \
  --title="Create apache virtualhost" \
  --text='Subdomain are case sencetive for Webroot folder ${subdomain} variable' \
  --focus-field=1 --center --window-icon="preferences-system" --width=600 \
  "${config[subdomain]}" "${config[domain]}" "${config[webmaster]}" "${config[webgroup]}" \
  "${config[webroot]}" "test" "${config[virtualhost]}" "${config[virtualport]}" "${config[serveradmin]}" 1)
formbutton="$?"

Answer 1

You need to handle the exit code of the command.

The exit status of the command is the exit status of last command executed.

Variable assignment is not a command.

So you can just do what's popular in set -e scripts:

formoutput=$(yad ...) || ret=$? && ret=$?

to catch the return value.

Or you can ignore the exit by invoking : command:

formoutput=$(yad ...) ||:

The ||: is really || with : command. The colon command returns exit status of zero, the exit status of the list of commands a || b a || b is the exit status of the last command executed in the list, as : always returns zero, the list of commands will also return zero exit status.

Or use if :

if ! formoutput=$(yad ...); then 
          echo "AAAA! yad failed! abort ship!" >&2
fi

Note that if command also has an exit status of the last command executed. So be aware that:

if true; then
    false
fi

will exit from your set -e script.

Answer 2

Try this:

set -e
false || echo $? && echo 0

Even though false exits with 1, you'll be able to capture this exit value in the middle (with $? ) without aborting the whole script.

If the script ( false ) didn't fail, the exit code is always zero so you can just put a zero on success.

Answer 3

I needed to use the operators in the other order for this to work

$ set -e
$ true || status=$? && status=$?; echo $status
0
$ false || status=$? && status=$?; echo $status
0
$ true && status=$? || status=$?; echo $status
0
$ false && status=$? || status=$?; echo $status
1