rename

To rename file(s).

Example:

Prompt> rename 's/pdb/ent/' *.pdb

This changes the name of all files whose name ends with ".pdb".

Nota bene:
The syntax for the substitution is like in sed or vi.
This means that, in the example above, only the first "pdb" string found is changed. For instance, a file named pdbxxx.pdb is renamed as follows: entxxx.pdb.