Update custom date field based on another date field when it is updated

[Peter Garncarek]

I am using Portfolio which has custom field "Target Start" date.  When this field is updated I want to automatically copy "Target Start" to custom field "IG1" (it is a date field also).

Based on what I read, a listener for "Issue Updated" event would do the trick.  I just need the simple code to copy value of "Target Start" to "IG1".  I have seen examples but nothing specific to this and I do not know enough to do this quickly and figure someone out there must have done this already and perhaps can help me with the code.

Or should I just make "IG1" a scripted field and not do a listener?