XML Catalog Manager (xmlcatmgr in its short form) is a small utility used
to manipulate SGML and XML catalogs.  It is extremely small and lightweight,
specially designed to be run from packaging systems.  Basically, it allows
adding and removing entries from catalogs in a completely automated way.

A catalog is a lookup mechanism used to translate entities into other
different entities.  They can, for example, map public identifiers to
local files or URIs.  This allows you to tell the parser where to look
for entities without having to modify the original document source.