Automate atom/group selections?

[pr19]

GROMACS version: 2021.3
GROMACS modification: Yes/No
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When running commands like gmx make_ndx and gmx cluster, I am prompted to select a group for the analysis. Is there a way I could modify the gmx command to automatically select the desired group(s)?

[jalemkul]

You can use echo to pass selections to any GROMACS utility.

echo X Y | gmx command ...