On 28 March 2011, Ford, Kevin wrote:

> I couldn't get Simon's MARC 21 Magic file to work.  Among other issues, 
> I received "line too long" errors.  But, since I've been curious about 
> this for sometime, I figured I'd take a whack at it myself.  Try this:

This is very nice!  Thanks.  I tried it on a bunch of MARC files I have, 
and it recognized almost all of them.  A few it didn't, so I had a closer 
look, and they're invalid.

For example, the Internet Archive's Binghamton catalogue dump:

http://ia600307.us.archive.org/6/items/marc_binghamton_univ/

$ file -m marc.magic bgm*mrc
bgm_openlib_final_0-5.mrc:         data
bgm_openlib_final_10-15.mrc:       MARC Bibliographic
bgm_openlib_final_15-18.mrc:       data
bgm_openlib_final_5-10.mrc:        MARC Bibliographic

But why?  Aha:

$ head -c 25 bgm_openlib_final_*mrc
==> bgm_openlib_final_0-5.mrc <==
01812cas  2200457   45x00
==> bgm_openlib_final_10-15.mrc <==
01008nam  2200289ua 45000
==> bgm_openlib_final_15-18.mrc <==
01614cam    00385   45  0
==> bgm_openlib_final_5-10.mrc <==
00887nam  2200265v  45000

As you say, the leader should end with 4500 (as defined at 
http://www.loc.gov/marc/authority/adleader.html) but two of those files 
don't.  So they're not valid MARC.  I'm sure any decent MARC tool can deal 
with them, since decent MARC tools are certainly going to be forgiving 
enough to deal with four characters that apparently don't even really 
matter.

So on the one hand they're usable MARC but file wouldn't say so, and on 
the other that's a good indication that the files have failed a basic 
validity test.  I wonder if there are similar situations for JPEGs or 
MP3s.

I think you should definitely submit this for inclusion in the magic file. 
It would be very useful for us all!

Bill

P.S. I'd never used head -c (to show a fixed number of bytes) before. 
Always nice to find a new useful option to an old command.

> #--------------------------------------------
> # MARC 21 Magic  (Second cut)
>
> # Set at position 0
> 0 	short	>0x0000
>
> # leader ends with 4500
>> 20	string	4500
>
> # leader starts with 5 digits, followed by codes specific to MARC format
>>> 0	regex/1	(^[0-9]{5})[acdnp][^bhlnqsu-z]	MARC Bibliographic
>>> 0	regex/1	(^[0-9]{5})[acdnosx][z]	MARC Authority
>>> 0	regex/1	(^[0-9]{5})[cdn][uvxy]	MARC Holdings
>>> 0	regex/1	(^[0-9]{5})[acdn][w]	MARC Classification
>>> 0	regex/1	(^[0-9]{5})[cdn][q]	MARC Community


-- 
William Denton, Toronto : miskatonic.org www.frbr.org openfrbr.org