Perlaccess : Tutorials : File and Directory
Renaming Files & Directories (12.4)
by Jacob A. Wheeler
http://www.bigresources.com

Renaming Files & Directories are pretty much the same. 

rename OLDNAME, NEWNAME
OLDNAME = Old File/Directory Name
NEWNAME = New File/Directory Name

Example: 
#!/usr/bin/perl
$new_file = "/path/to/new/file.txt"
$old_file = "/path/to/old/file.txt";
renameStuff();
sub renameStuff {
rename($old_name,$new_name) or "Error renaming file ($old_name)\n";
exit();
}