What is catalog command and how is it used? | Oracle DBA

Catalog command is used to register different types of information with RMAN's repository.
Catalog command can be used to perform the following tasks:
i. Add information of backup pieces and image copies in the repository that are on disk a Record information about the level 0 backup in the RMAN repository.
ii. Record information about the copy taken by the operating system
Following examples show the use of catalog command:
1.Catalog an archive log — CATALOG ARCHIVELOG '<filename>';
2.Catalog a data file copy — CATALOG DATAFILECOPY '<filename>' Level <level>;