cif_merge(1) on Linux
The text 86bb7fcd9a34, as Debian 10 (Buster) shipped it.
Merge data values in identical data blocks of multiple CIFs. Unique data items are combined into a single data block of the output CIF; data items with equivalent values are silently merged into one. When a value differs for the same data item and the same data block in two files, a warning (error) is issued.