Scripting

I am trying to push a small script to a test mac.  The script will make the current logged in user an admin of the Mac.  The script works when I pass the username over to the Mac.  But as soon as I try to use a variable to get the logged in current user, the script fails.

This works (the current username is user2)

dseditgroup -o edit -a user2 -u localadmin -P mm1007mm -t user admin

This fails with the following (using $USER to get the current logged in user)

dseditgroup -o edit -a $USER -u localadmin -P mm1007mm -t user admin

2014-04-22 10:03:46: Alert not enabled, moving to next phase....

2014-04-22 10:03:52: Sending script script.sh to client....

2014-04-22 10:03:57: Script sent

2014-04-22 10:03:57: Executing script....

2014-04-22 10:04:01: Error 64 received while executing script

Any help would be greatly appreciated.