This is a python script (python/coords/RadCon.py) that takes as input a field size and the name of the unit this size is given in. The result (to standard out) is the size in arcsec, arcmin, degrees.

%  RadCon.py 20.0 arcsec 
20.000000000 0.333333 0.006

% RadCon.py 20.0 arcmin 
1200.000000000 20.000000 0.333

% RadCon.py 20.0 deg 
72000.000000000 1200.000000 20.000

% RadCon.py 20 gog 
0.000000000 0.000000 0.000

Using RadCon.py in a script I typically redirect the 
output to a file (ptools.2) that I can then read 
to set variables within the bash script: 

RadCon.py $3 arcmin >ptools.2 
read Rsec Rmin Rdeg < ptools.2

N.B. In this case arg3 is the field radius in arcminutes.