[Magic-dev] ~/.magic breaks UNIX 'file' command on OS X

[David Fang]

Hi Calin,

> This is the first time i hear about it. Since is not documented in file
> man page on OSX it's a bug in file on OSX.

	Or just missing documentation.

> On linux I never had that problem. I checked on internet for other
> systems and at least OpenBSD, HP-UX, IRIX, Solaris don't have the
> problem that you describe.

	Well not *every* unix variant is structured the same way.  Mac OS
X 10.4 (darwin 8) was derived from FreeBSD 5, but not every aspect was
mirrored.

> > 	% file
> > 	file: could not find any magic files!
> This is a bug. file on unix systems reads /etc/magic not ~/.magic

According to my man file:

FILES
       /usr/share/file/magic.mgc
              Default compiled list of magic numbers

       /usr/share/file/magic
              Default list of magic numbers

       /usr/share/file/magic.mime.mgc
              Default compiled list of magic  numbers,  used  to  output mime
              types when the -i option is specified.

       /usr/share/file/magic.mime
              Default  list  of  magic numbers, used to output mime types when
              the -i option is specified.

       /etc/magic
              Local additions to magic wisdom.


	There is no /etc/magic on my system (10.4) nor on 10.3.  It's
merely optional for local extensions.  One has to create it and put
custom files there.  No mention of $HOME/.magic, but my *observation* is
that it somehow overrides the other file-magic paths.  Even an empty
.magic file breaks file.

% ls -l /usr/share/file
total 5104
-rw-r--r--   1 root  wheel   358659 Mar 20 19:03 magic
-rw-r--r--   1 root  wheel  2100032 Mar 20 19:03 magic.mgc
-rw-r--r--   1 root  wheel    30287 Mar 20 19:03 magic.mime
-rw-r--r--   1 root  wheel   115104 Mar 20 19:03 magic.mime.mgc

> > then you have a problem.  The obvious workaround of course, is to
> > move .magic out of the way during such compiles.  Has this been a known
> > problem?  Perhaps someone with more knowledge on the subject could
> > offer a better solution?
>
> This has never been a problem. I know magic from about 5 years and
> never heard of such a problem.

	Tried using it on Mac OS X?  :)  I guess the conclusion is that
other unices' `file' command just doesn't use $HOME/.magic, it may be as
simple as that.  Perhaps I'll poke around the Darwin newsgroups or look
at the source myself.

> Sidenote: maybe it's an undocumented behaviour if it doesn't have a
> /etc/magic file to look in home directory for a ~/.magic file.
> Do you have a /etc/magic file ?

	My feeling is that it's just plain undocumented.
	Thanks for the feedback.

David Fang
Computer Systems Laboratory
Electrical & Computer Engineering
Cornell University
http://www.csl.cornell.edu/~fang/ -- *gag* work in progress