Invalid Command Name "open"

I’m attempting to create a log file using OpenOCD 0.10.0 using the simple code:

set f [open $logfile w]

Running this I get the error invalid command name “open”. I understand that jim tcl is a cut-down version of tcl, but is this one of the commands that has been removed? I have used the same bit of code successfully on an earlier version of OpenOCD.

Is there any way that I can get this to work?