# Minitar#tar? and inclusion in Ruby?

**URL:** <https://www.ruby-forum.com/t/minitar-tar-and-inclusion-in-ruby/96875>\
**Category:** Ruby\
**Created:** [July 3, 2006, 12:57am UTC](https://www.ruby-forum.com/t/minitar-tar-and-inclusion-in-ruby/96875 "2006-07-03T00:57:04Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [July 3, 2006, 12:57am UTC](https://www.ruby-forum.com/t/minitar-tar-and-inclusion-in-ruby/96875/1 "2006-07-03T00:57:04Z")

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Using Archive::Tar:Minitar, is there any way to quickly check if a file  
is a tar file or not?

Also I would like to recommend Austin’s lib for inclusion in Ruby. We  
already have Zlib so it makes sense to provide for tar.gz files.  
Although I think maybe simplify the naming to just Archive::Tar --no  
Minitar. Hopefully it will get some additonal features eventually and  
not be so “mini” 😉 In so doing, perhaps Zlib belongs in Archive  
namespace too?

Thanks,  
T.

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [July 3, 2006, 2:11am UTC](https://www.ruby-forum.com/t/minitar-tar-and-inclusion-in-ruby/96875/2 "2006-07-03T02:11:52Z")

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removed\_email\_address@domain.invalid wrote:

> Using Archive::Tar:Minitar, is there any way to quickly check if a file  
> is a tar file or not?

To answer my own question, sadly, “no”:

Magic bytes  
None.  
However, identification of tar files is not limited to looking at  
the file extension. Each tar archive entry header also stores a  
checksum on itself. Thus, reading the first 512 bytes of a potential  
tar file, creating that checksum and comparing it to the stored  
checksum will tell if the file really is in tar format.

That’s too complex for efficent checking. OTOH, Luckly gzips are easy  
to identify. Not tested but basically:

class File  
# Is a file a gzip file?  
def self.gzip?( file )  
File.open(file,‘rb’) { |f|  
return false unless f.getc == 0x1f  
return false unless f.getc == 0x8b  
}  
end  
end

Might be worth adding to Zlib (assuming it’snot already there --I  
didn’t see it).

T.

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [July 3, 2006, 2:58am UTC](https://www.ruby-forum.com/t/minitar-tar-and-inclusion-in-ruby/96875/3 "2006-07-03T02:58:32Z")

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On 7/2/06, removed\_email\_address@domain.invalid [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Using Archive::Tar:Minitar, is there any way to quickly check if a file  
> is a tar file or not?
> 
> Also I would like to recommend Austin’s lib for inclusion in Ruby. We  
> already have Zlib so it makes sense to provide for tar.gz files.  
> Although I think maybe simplify the naming to just Archive::Tar --no  
> Minitar. Hopefully it will get some additonal features eventually and  
> not be so “mini” 😉 In so doing, perhaps Zlib belongs in Archive  
> namespace too?

Actually, Archive::Tar::Minitar will be deprecated hopefully by the  
end of the year. Members of TRUG started on a project (RAT) to replace  
it with a port of libarchive at a hackathon earlier this year. This  
didn’t produce something usable, but work will continue in other  
hackathons later this year and something should be usable (hopefully)  
by RubyConf.

There’s a lot that Minitar can’t do – and little value in adding it  
considering the options that libarchive give us.

-austin

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [July 3, 2006, 12:43pm UTC](https://www.ruby-forum.com/t/minitar-tar-and-inclusion-in-ruby/96875/4 "2006-07-03T12:43:28Z")

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Austin Z. wrote:

> Actually, Archive::Tar::Minitar will be deprecated hopefully by the  
> end of the year. Members of TRUG started on a project (RAT) to replace  
> it with a port of libarchive at a hackathon earlier this year. This  
> didn’t produce something usable, but work will continue in other  
> hackathons later this year and something should be usable (hopefully)  
> by RubyConf.

Nice. I look foward to using libarchive – really hope it pans out. I  
need it to pan out!

Thanks Austin,  
T.

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [July 3, 2006, 2:49pm UTC](https://www.ruby-forum.com/t/minitar-tar-and-inclusion-in-ruby/96875/5 "2006-07-03T14:49:47Z")

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On 7/3/06, removed\_email\_address@domain.invalid [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> ```
> However, identification of tar files is not limited to looking at
> 
> ```
> 
> the file extension. Each tar archive entry header also stores a  
> checksum on itself. Thus, reading the first 512 bytes of a potential  
> tar file, creating that checksum and comparing it to the stored  
> checksum will tell if the file really is in tar format.
> 
> That’s too complex for efficent checking. OTOH, Luckly gzips are easy  
> to identify. Not tested but basically:

Might it be sufficent for your purpose to check if the first 100 bytes  
are  
of the form ASCI+\0\* ?  
Sorry I do not have a uft8 fs handy to see if the ASCI+ contraint can be  
easily checked in that case.

Cheers  
Robert

class File

> didn’t see it).
> 
> T.

–  
Deux choses sont infinies : l’univers et la bêtise humaine ; en ce qui  
concerne l’univers, je n’en ai pas acquis la certitude absolue.

- Albert Einstein