Bash compare output of command to empty text string

Question

I am trying to write a function that compares the output of a command and runs a loop until it returns nothing. When I run it, it acts like the condition has not been met and the script is forever stuck in the while loop, even though if I run the command at the prompt it returns nothing. Any help is greatly appreciated. Machine is Mac OS 10.9 which is why the syntax of su is a little funky.

stopvm ()
{
    su macadmin -c "VBoxManage controlvm tjfog acpipowerbutton"
    while [`su macadmin -c 'VBoxManage list runningvms | grep tjfog'` != ""]
    do
        echo "Waiting for the VM to shutdown"
        sleep 3
    done
}

Running at the prompt returns the following.

bash-3.2# su macadmin -c VBoxManage list runningvms | grep tjfog
bash-3.2#

Thanks!

anubhava · Accepted Answer · 2013-12-13 21:16:25Z

3

[ and ] require spaces inside after [ and before ].

But you can rewrite your while condition as:

while su macadmin -c 'VBoxManage list runningvms | grep -q tjfog'
do
    echo "Waiting for the VM to shutdown"
    sleep 3
done

answered Dec 13, 2013 at 21:16

anubhava

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