[TAG] Another 2 cent tip for you

[Lew Pitcher]

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Hi, guys.

I sent this in a couple of months ago, but it seems to have disappeared into 
the aether and not made it to your fine publication. So, assuming that it 
wasn't rejected, but had just been missed, I decided that I should try again.

Here's a little tip I gathered from some conversation going on in the 
alt.os.linux newsgroup a couple of months ago. I contacted the people 
involved in the news thread and they all agreed that I could submit the 
conclusions of the thread as a Two Cent Tip (with proper accreditation, of 
course). So, thanks to Michael Heiming and Chris F. A. Johnson, here's a Two 
Cent Tip for you...


Over in news:alt.os.linux, a reader posted a question that asked how to make
Linux use "file associations" (sort of like MSWindows) so that the user just
types the name of the data file at the commandline, and the sutiable
application starts up and processes it. The example was wanting xmms to play
an MP3 just by typing the MP3's filename at the command prompt.

This lead into a discussion amongst various alt.os.linux participants, 
primarily  Michael Heiming and Chris F.A. Johnson,  about "binfmt_misc", and 
how it could be used to satisfy MSWindow'ish "file associations". For those 
who don't know, you can "register" a command interpreter through a /proc 
entry, so that, when you try to run a file that needs that command 
interpreter, the system will start up the program for you. This is how Linux 
recognizes executable shell scripts in order to start the shell interpreter 
on them, and how it recognizes executable java byte code, in order to run the 
java interpreter on it, when you type it's name at the command prompt. 

To use this feature, you need to mount the "binfmt_misc" pseudo-filesystem, so
as root,
  mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
(or add the appropriate line to your /etc/fstab, and have it mounted
automatically at the next boot). Now, (again, as root) tell Linux what 
interpreter to use by "echo"ing an association string into 
the /proc/sys/fs/binfmt_misc/register pseudo-file. In this case, we want to 
the string to indicate that any 'executable' file with the 'extension' 
of .mp3 is to be interpreted by /usr/bin/xmms, so the
registration strings are
  echo ":xmms:E::mp3::/usr/bin/xmms:" > /proc/sys/fs/binfmt_misc/register
  echo ":mps:E::mp3::/usr/bin/xmms:" >/proc/sys/fs/binfmt_misc/register
  echo ":ogg:E::ogg::/usr/bin/xmms:" >/proc/sys/fs/binfmt_misc/register
  echo ":m3u::E:m3u::/usr/bin/xmms:" >/proc/sys/fs/binfmt_misc/register

Now, when we (as a regular user)
  ~ $ chmod u+x my_life_changed.mp3
and then
  ~ $ my_life_changed.mp3
up pops XMMS and the music plays on.

The format and variations of the "registration" string are documented
in /usr/src/linux/Documentation/binfmt_misc.txt. 

Kewl, eh?

My thanks to Michael Heiming and Chris F. A. Johnson for pointing out
how to do this.
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