If you did want to move to the Exec binding, you’d put the command you want to execute under Command. Per the Exec binding docs " * the current (or last) command to the input channel (see below, example: %2$s)" so the command would be:
This Thing will have a number of Channels associated with it. You will link a String Item to the Input Channel and sendCommand your errMsg to that String Item to cause the command to be run. The output of the command will be updated to a String Item linked to the Output Channel.
Note that you must add that command string as it appears in the whitelist (see the docs).