$ gemmi grep -h
Usage: gemmi grep [options] TAG FILE_OR_DIR_OR_PDBID[...]
       gemmi grep -f FILE [options] TAG
Search for TAG in CIF files.
By default, recursive directory search checks only *.cif(.gz) files.
To change it, specify --name=* or --name=*.hkl.

Options:
  -h, --help               display this help and exit
  -V, --version            display version information and exit
  -v, --verbose            print additional messages to stderr
  -f, --file=FILE          obtain file (or PDB ID) list from FILE
  --name=PATTERN           filename glob pattern used in recursive grep; by
                           default, *.cif and *.cif.gz files are searched
  -m, --max-count=NUM      print max NUM values per file
  -O, --one-block          optimize assuming one block per file
  -a, --and=tag            Append delimiter (default ';') and the tag value
  -d, --delimiter=DELIM    CSV-like output with specified delimiter
  -n, --line-number        print line number with output lines
  -H, --with-filename      print the file name for each match
  -b, --no-blockname       suppress the block name on output
  -t, --with-tag           print the tag name for each match
  -l, --files-with-tag     print only names of files with the tag
  -L, --files-without-tag  print only names of files without the tag
  -c, --count              print only a count of values per block or file
  -r, --recursive          ignored (directories are always recursed)
  -w, --raw                include '?', '.', and string quotes
  -s, --summarize          display joint statistics for all files