Bash: How can I check the return value of a command

Question

I am new to bash scripting and want to write a short script, that checks if a certain program is running. If it runs, the script should bring the window to the foreground, if it does not run, the script should start it.

#!/bin/bash

if [ "$(wmctrl -l | grep Wunderlist)" = ""]; then
    /opt/google/chrome/google-chrome --profile-directory=Default --app-id=ojcflmmmcfpacggndoaaflkmcoblhnbh
else
    wmctrl -a Wunderlist
fi

My comparison is wrong, but I am not even sure what I should google to find a solution. My idea is, that the "$(wmctrl -l | grep Wunderlist)" will return an empty string, if the window does not exist. I get this error when I run the script:

~/bin » sh handle_wunderlist.sh                                       
handle_wunderlist.sh: 3: [: =: argument expected

Answer 1

You need a space before the closing argument, ], of the [ (test) command:

if [ "$(wmctrl -l | grep Wunderlist)" = "" ]; then
    ....
else
    ....
fi

As a side note, you have used the shebang as bash but running the script using sh (presumably dash, from the error message).