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bug#17640: grep with -m reads the entire input
From: |
Jim Meyering |
Subject: |
bug#17640: grep with -m reads the entire input |
Date: |
Fri, 30 May 2014 08:58:44 -0700 |
On Fri, May 30, 2014 at 8:56 AM, Jim Meyering <address@hidden> wrote:
> On Thu, May 29, 2014 at 10:45 PM, Marc Aldorasi <address@hidden> wrote:
>> With grep 2.18, the -m option would cause grep to stop reading input
>> after printing the requested number of matching lines. With version
>> 2.19, grep reads the entire input before exiting. Interestingly, grep
>> does not read the entire input if the -c or -C0 options are added in
>> addition to -m, and also when using -l or -q instead of -m. I believe
>> this is caused by commit 5122195.
>
> Thanks a lot for the report. Just in time.
> I confirm that it's a bug introduced in 2.19.
> To test, run "seq 1000000 > million", then
> "strace -e read grep 0 million" first using grep-2.18
> (shows just a few read syscalls), and then with 2.19,
> which shows grep reading the entire million-line file.
Correction: to reproduce, you'll have to insert -m1 in that grep command.
> Here's an incomplete patch. Obviously there's a lot more
> to be added, including NEWS and a nontrivial test. This
> was introduced by commit v2.18-140-g6f07900