afni.nimh.nih.gov

The pair of files forms a single dataset. Generally one would
not use either as part of the dataset name, though it is okay.

These examples would all do the same thing:

3dresample -master irf+orig -input mask+orig -prefix mask_irf
3dresample -master irf+orig.HEAD -input mask+orig.HEAD -prefix mask_irf
3dresample -master irf+orig.BRIK -input mask+orig.BRIK -prefix mask_irf

- rick