Re: [9fans] a question of file and the history of magic

[Jeff Sickel <jas@corpus-callosum.com>]

On Jul 6, 2008, at 2:30 PM, erik quanstrom wrote:

>> This addition helped my scripts become a little more streamlined, but
>> of course puts in an additional entry into the source file I need to
>> track.  As file name extensions don't always work across all sorts of
>> systems, many still hamstrung by 8.3, what is the preferred or
>> recommend mechanism for checking file types the Plan 9 way since we
>> no
>> longer have the System V magic?
>
> i'm pretty confused by what you're saying here.  why doesn't file(1)
> work?
> are you saying there's something wrong with editing the source as
> opposed
> to to editing a configuration file?


File does work; until I need to check for something not in its
compiled-in magic tables.  So I patch the code and it works better
than many other options I've tried while still letting me use rc to
script out things I need to get done without the restart time of
trying to remember what the script does when I need to add to it later
(unlike the brick wall I continually hit all the time when using Perl).

In a sense, the question is more about the historical change and/or
adoption of a new file command for Plan 9 that doesn't use a magic
file for references.  Why opt out of a magic file other than the
obvious performance hit of scanning it each run?  Is it worth
repeating the old forms that used magic, or has anyone in the Plan 9
community already improved upon the idea and introduced a new, more
adaptable tool?

> either way your system is equally non-standard.  in either event,
> submitting a patch and having it accepted is the only way around this.

The beauty of standards is there are so many to choose from -- oft
quoted and most likely misappropriated from somewhere else.

> 	dd -if $infile -bs $nbytes -count 1 | xd

dang, I almost always forget about dd for some reason.  Though in that
case I'd need to pull in Plan 9's version of dd into p9p since the
arguments to dd are different on almost every system I use: Plan 9,
various Linux distros, Solaris, OS X, ...

-jas