Getting forces within a distance cutoff of an index atom : gmx traj

GROMACS version:2016.5
GROMACS modification: No
Hi all ,
I am using gmx traj to get all the forces on the index atom with the following command
gmx traj -s %s_md.tpr -f %s_md.xtc -n probe.ndx -of %s_probeF.xvg

How can I get the all the force within a certain distance cutoff from my index atom?
For example instead of forces due to all the atoms in the box, I want forces within 10 angstrom of my index atom.
Thanks in advance.

gmx traj only prints out the forces that were already computed by mdrun. If you want only forces acting on an atom within 10 Å then I suggest specifying plain cutoffs (no long-range algorithms) in a new .mdp file and using mdrun -rerun to re-evaluate energies and forces.