Update: Now that it\'s 2016 I\'d use PowerShell for this unless there\'s a really compelling backwards-compatible reason for it, particularly because of the regional setting
I had a similar problem. I have an automatic daily download from an FTP server of an encrypted file. I wanted to decrypt the file using gpg, rename the file to the current date (YYYYMMDD format) and drop the decrypted file into a folder for the correct department.
I went through several suggestions for renaming the file according to date and was having no luck until I stumbled upon this simple solution.
for /f "tokens=1-5 delims=/ " %%d in ("%date%") do rename "decrypted.txt" %%g-%%e-%%f.txt
It worked perfectly (i.e., the filename comes out as "2011-06-14.txt").
(Source)