Detecting failure of a Bash “export” value

问题

In Bash I'm executing a command and putting the result in a variable like this:

export var=`svn ls`

But if SVN fails for some reason--say it returns a non-zero error code--export still returns status code 0. How do I detect if the executed command fails?

回答1:

var=`svn ls`
if [[ $? == 0 ]]
then
        export var
else
        unset var
fi

$? is the exit code of the last command executed, which is svn ls here.

jmohr's solution is short and sweet. Adapted mildly,

var=`svn ls` && export var || unset var

would be approximately equivalent to the above (export of a valid identifier will never fail, unless you've done something horrible and run out of environment space). Take whatever you want -- I use unset just to avoid $var possibly having a value even though it's not exported.

回答2:

var=`svn ls` && export var

回答3:

I had similar problem, it can be done like this:

rm -f error_marker_file
export var=`svn ls || touch error_marker_file`

[ -f error_marker_file ] && echo "error in executing svn ls"

回答4:

export FOO=$(your-command) || echo "your-command failed"

来源：https://stackoverflow.com/questions/247706/detecting-failure-of-a-bash-export-value