GNU bug report logs - #51921
Anything like ztail

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Peng Yu <pengyu.ut <at> gmail.com>
To: bug-gzip <at> gnu.org
Subject: Anything like ztail
Date: Wed, 17 Nov 2021 07:08:48 -0600

Hi,

Is there a more efficient way to perform ztail. I could use 'zcat f.gz
| tail'. But this means that it needs to go through the file until the
end. It would be more efficient to just check the end (as `tail f.txt`
does it). Is there a way to make ztail more efficient?

-- 
Regards,
Peng

Message #8 received at 51921 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Peng Yu <pengyu.ut <at> gmail.com>
Cc: 51921 <at> debbugs.gnu.org
Subject: Re: bug#51921: Anything like ztail
Date: Wed, 17 Nov 2021 12:33:33 -0800

On 11/17/21 05:08, Peng Yu wrote:
> Is there a way to make ztail more efficient?

Not in general, no. The compressed file can't be decompressed from 
random locations.

There might be some options for doing what you're suggesting if 
--rsyncable is used during compression (which it usually isn't) and if 
someone would like to code up something for gzip (which would be 
nontrivial).

Message #13 received at 51921 <at> debbugs.gnu.org (full text, mbox):

From: Stephen Kitt <steve <at> sk2.org>
To: Peng Yu <pengyu.ut <at> gmail.com>
Cc: Paul Eggert <eggert <at> cs.ucla.edu>, 51921 <at> debbugs.gnu.org
Subject: Re: bug#51921: Anything like ztail
Date: Wed, 17 Nov 2021 22:58:14 +0100

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On Wed, 17 Nov 2021 12:33:33 -0800, Paul Eggert <eggert <at> cs.ucla.edu> wrote:
> On 11/17/21 05:08, Peng Yu wrote:
> > Is there a way to make ztail more efficient?  
> 
> Not in general, no. The compressed file can't be decompressed from 
> random locations.
> 
> There might be some options for doing what you're suggesting if 
> --rsyncable is used during compression (which it usually isn't) and if 
> someone would like to code up something for gzip (which would be 
> nontrivial).

gztool (https://github.com/circulosmeos/gztool) can be used to create
additional indexes and then use that to access a compressed file randomly
without decompressing everything; it supports tail-style operation as well.

Whether it’s actually useful will depend on the scenario.

Regards,

Stephen

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