GNU bug report logs - #42402
Enhancement request re zcat with empty files

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

From: Peter Horn <peter.horn <at> bigpond.com>
To: bug-gzip <at> gnu.org
Subject: Enhancement request re zcat with empty files
Date: Fri, 17 Jul 2020 13:42:04 +1000

Hello list,

This is my first post here, so apologies in advance for whatever I get 
wrong.

I am asking for an enhancement to zcat, that it should silently ignore 
empty files, either always, or (if that conflicts with POSIX or some 
other standard), by a command line option.

My use case is as follows:
I maintain a server, and have occasion to scan log files for specific items.
As is typical in a logrotate environment, the files are something like

xyz.log              current
xyz.log.1           previous
xyz.log.2.gz
xyz.log.3.gz      etc etc

Most of the time I can search for something by

zgrep 'target' xyz*

But, wanting to further process a number of entries, I tried the obvious

zcat xyz* | awk ...

which results in

gzip: xyz.log.1: unexpected end of file

I note that it correctly handles archives with no content (just the 20 
byte header)

Regards,
Peter

Message #8 received at 42402 <at> debbugs.gnu.org (full text, mbox):

From: Bob Proulx <bob <at> proulx.com>
To: Peter Horn <peter.horn <at> bigpond.com>
Cc: 42402 <at> debbugs.gnu.org
Subject: Re: bug#42402: Enhancement request re zcat with empty files
Date: Fri, 17 Jul 2020 23:45:22 -0600

Peter Horn wrote:
> But, wanting to further process a number of entries, I tried the obvious
> zcat xyz* | awk ...
> which results in
> gzip: xyz.log.1: unexpected end of file

To perhaps help work around the issue you have raised I'll just
suggest that 'zmore' and 'zless' can be (ab)used in this case.  They
are both the same.  And also though you mentioned 'zgrep' it can also
be used early in the pipeline.  Try it this way.

  zmore xyz.log* | awk ...
  zless xyz.log* | awk ...
  zgrep whatever xyz.log* | awk ...

It's somewhat backing into the solution but perhaps useful for you in
the toolbox regardless.

Bob

Message #13 received at 42402-done <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Peter Horn <peter.horn <at> bigpond.com>
Cc: 42402-done <at> debbugs.gnu.org
Subject: Re: Enhancement request re zcat with empty files
Date: Wed, 6 Apr 2022 17:08:17 -0700

> I am asking for an enhancement to zcat, that it should silently ignore 
> empty files, either always, or (if that conflicts with POSIX or some 
> other standard), by a command line option.

zcat -f does what you're asking for. For example:

$ touch empty
$ echo something | gzip >abc.gz
$ zcat -f *
something

Since the -f option satisfies your request I'll close the bug report.

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