Note: Most users will find that using the install-fieldmap.sh script suffices
for default field map installation:

See https://www.muec-uk.org/trac/browser/COMET/comet_g4_install/trunk/install-defaultFieldMap.sh
and use
svn checkout https://www.muec-uk.org/muecuk/COMET/comet_g4_install/trunk
to obtain the install script.

How to checkout just one file (such as defaultFieldMap.dat.gz)
==============================================================

To check out the single large file defaultFieldMap.dat.gz among all the
huge files inside the directory you can see in
https://www.muec-uk.org/trac/browser/COMET/fieldMaps/110812

Do this

  $svn checkout 'https://www.muec-uk.org/muecuk/COMET/fieldMaps/110812/' 110812 --depth empty

# this checks out the directory 110812 without anything inside it
# note also you replace "trac/browser" in the URL with "muecuk" to turn
# it into  a URL for SVN

  $cd 110812/

# enter the directory. It has the usual .svn directory in it

  $svn update defaultFieldMap.dat.gz

# Update the directory with just the file you need.