$ gemmi convert -h
Usage:
 gemmi convert [options] INPUT_FILE OUTPUT_FILE

with possible conversions between PDB, mmCIF and mmJSON.
FORMAT can be specified as one of: mmcif, mmjson, pdb, ccd (read-only).
ccd = coordinates of a chemical component from CCD or monomer library.

General options:
  -h, --help              Print usage and exit.
  -V, --version           Print version and exit.
  -v, --verbose           Verbose output.
  --from=FORMAT           Input format (default: from the file extension).
  --to=FORMAT             Output format (default: from the file extension).

CIF output options:
  --pdbx-style            Similar styling (formatting) as in wwPDB.
  -b NAME, --block=NAME   Set block name and default _entry.id
  --sort                  Sort tags in alphabetical order.
  --skip-category=CAT     Do not output tags starting with _CAT

PDB input options:
  --segment-as-chain      Append segment id to label_asym_id (chain name).
  --old-pdb               Read only the first 72 characters in line.
  -L, --force-label       Add label_seq_id even if SEQRES is missing

PDB output options:
  --short-ter             Write PDB TER records without numbers (iotbx compat.).
  --linkr                 Write LINKR record (for Refmac) if link_id is known.

Any output options:
  --minimal               Write only the most essential records.
  --shorten               Shorten chain names to 1 (if # < 63) or 2 characters.
  --rename-chain=OLD:NEW  Rename chain OLD to NEW (--rename-chain=:A adds
                          missing chain IDs).
  -s FILE                 Use sequence from FILE (PIR or FASTA format), which
                          must contain either one sequence (for all chains) or
                          as many sequences as there are chains.
  --anisou=yes|no|heavy   Add or remove ANISOU records.

Macromolecular operations:
  --expand-ncs=dup|new    Expand strict NCS specified in MTRIXn or equivalent.
                          New chain names are the same or have added numbers.
  --assembly=ID           Output bioassembly with given ID (1, 2, ...).
  --remove-h              Remove hydrogens.
  --remove-waters         Remove waters.
  --remove-lig-wat        Remove ligands and waters.
  --trim-to-ala           Trim aminoacids to alanine.

When output file is -, write to standard output.