Linux: rename file but keep extension?

Here's an answer for the bonus question.

I actually want to put a photo's creation date into its filename, to get something like 20091231 2359 New Year.jpg. I'm afraid that I need some non-trivial combination of commands to achieve that?

Assuming you want to take the photo's creation date from the EXIF data, you'll need a separate tool for that. Luckily it turns out that jhead offers a trivial way to do exactly what you want, with its -n option.

$ jhead -h
 [...]

 -n[format-string]

             Rename files according to date.  Uses exif date if present, file
             date otherwise.  If the optional format-string is not supplied,
             the format is mmdd-hhmmss.  If a format-string is given, it is
             is passed to the 'strftime' function for formatting
             In addition to strftime format codes:
             '%f' as part of the string will include the original file name
             [...]

Here's an example:

$ jhead -n%Y-%m-%d-%f New_year.jpg   
New_year.jpg --> 2009-12-31-New_year.jpg

Edit: Of course, to do this for a bunch of photos, it'd be something like:

$ for i in *jpg; do jhead -n%Y-%m-%d-%f $i; done

To tweak the date formatting to your liking, take a look at the output of date --help, for example; it will list the available format codes.

(jhead is widely available for different systems. If you are e.g. on Ubuntu or Debian, simply type sudo apt-get install jhead to install it.)

For just the renaming part, the 'rename' program will work. It's the same as the example you saw in the man page, just switched around.

justin@eee:/tmp/q$ touch myfile.{a,b,c,d}
justin@eee:/tmp/q$ ls
myfile.a  myfile.b  myfile.c  myfile.d
justin@eee:/tmp/q$ rename -v s/myfile/yourfile/ myfile.*
myfile.a renamed as yourfile.a
myfile.b renamed as yourfile.b
myfile.c renamed as yourfile.c
myfile.d renamed as yourfile.d
justin@eee:/tmp/q$ ls
yourfile.a  yourfile.b  yourfile.c  yourfile.d
justin@eee:/tmp/q$ 

betelgeuse:tmp james$ ls myfile.* yourfile.*
ls: yourfile.*: No such file or directory   
myfile.a    myfile.b
betelgeuse:tmp james$ for file
> in myfile.*
> do
> mv "${file}" "`echo $file | sed 's/myfile\./yourfile./'`"
> done
betelgeuse:tmp james$ ls myfile.* yourfile.*
ls: myfile.*: No such file or directory
yourfile.a  yourfile.b

The key is that, if you've seen an example which shows how to munge one part of the filename with a regex, that's the only example you need. Extensions have no special status on unix filesystems - they're just a part of the filename that happens to be after a . character.