atw: screen captures for Unix environment

Howdy austechies

Does anybody know of a program/utility (preferably shareware or
freeware!) for taking screen captures in a Unix environment?
I've trawled around the web for a while and found some references to
programs xv and xgrab (to capture window in Unix machine). 
But I don't know how to get or use these programs - assuming they can do
the job. 

Thanks in anticipation, 

Gerry Gowan
Terra Firma Baseline project
---------------------------
Telstra CNO
Ground floor, 300 Exhibition Street,
Melbourne

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