mv  -  move or rename a file

     mv name1 name2

     Mv changes the name of name1 to name2.  If name2 is a direc-
     tory, name1 is moved to that directory with its original
     file-name.  Directories may only be moved within the same
     parent directory (just renamed).

     If name2 already exists, it is removed before name1 is
     renamed.  If name2 has a mode which forbids writing, mv
     prints the mode and reads the standard input to obtain a
     line; if the line begins with y, the move takes place; if
     not, mv exits.

     If name2 would lie on a different file system, so that a
     simple rename is impossible, mv copies the file and deletes
     the original.

     It should take a -f flag, like rm, to suppress the question
     if the target exists and is not writable.