Data can be piped into m.proj2 only if the proj1 and proj2 parameters
are supplied. This is one of the bugs(?) with the program. For example:
 
cat ll | m.proj2 proj1=proj=ll
proj2=proj=utm,a=6378137.0000000000,es=0.0066943800,zone=20,unfact=1.00
 
will work ... but
 
cat ll | m.proj2
 
will not.
 
I suspect that a good programmer could fix this. Also, you can just run
m.proj2 by itself and enter coordinates individually.
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A datum is silently ignored.
