[debbugs-tracker] bug#18076: closed (Lines are not ignored by option -I if they are followed by a line with a difference)

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Your message dated Tue, 22 Jul 2014 10:58:58 -0600
with message-id <address@hidden>
and subject line Re: [bug-diffutils] bug#18076: Lines are not ignored by option 
-I if they are followed by a line with a difference
has caused the debbugs.gnu.org bug report #18076,
regarding Lines are not ignored by option -I if they are followed by a line 
with a difference
to be marked as done.

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18076: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=18076
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--- Begin Message --- Subject: Lines are not ignored by option -I if they are followed by a line with a difference Date: Tue, 22 Jul 2014 14:59:43 +0800

Package: diffutils

Version: 3.3

When 2 (or more) consecutive lines are different between the two compared files, they are ignored by option -I if all of them are ignored; if the last line is not ignored, all the lines are returned by diff tool (instead of only the last line).

Although the documentation clearly indicates this as nominal, it looks strange while looking at the results to have lines that we supposed to have been ignored.

------------------
To reproduce:
1. Create 2 files (e.g. File1.txt and File2.txt) having 2 consecutive different lines (e.g. lines 2 and 3)
2. Run diff with option -I including a pattern matching line 2
3. Observe that diff returns differences for both lines 2 and 3

Note: the files attached could be used as an example with the command line
diff -I "^IGNORE:.*quot; File1.txt File2.txt
The difference is as follows:
2,3c2,3
< IGNORE: Line to be ignored with value = 1
< Different line (version A)
---
> IGNORE: Line to be ignored with value = 2
> Different line (version B)

Jean-Francois Thuong

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File1.txt
Description: Text document

File2.txt
Description: Text document

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--- Begin Message --- Subject: Re: [bug-diffutils] bug#18076: Lines are not ignored by option -I if they are followed by a line with a difference Date: Tue, 22 Jul 2014 10:58:58 -0600 User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0

tag 18076 notabug
thanks

On 07/22/2014 12:59 AM, Jean-Francois Thuong wrote:

> To reproduce:
> 1. Create 2 files (e.g. File1.txt and File2.txt) having 2 consecutive
> different lines (e.g. lines 2 and 3)
> 2. Run diff with option -I including a pattern matching line 2
> 3. Observe that diff returns differences for both lines 2 and 3

Thanks for the report.  However, this is not a bug, but documented
behavior.  -I only suppresses entire hunks where EVERY difference in the
hunk matches the regex.

The mode of operation you are requesting, where diff ignores lines that
match the regex prior to doing the comparison (although line numbers are
then a bit off), can be accomplished via this trick in bash:

patt='^IGNORE:'
diff <(sed "/$patt/d" File1.txt) <(sed "/$patt/d" File2.txt)

Maybe it's worth a new option to diff to allow this mode of operation by
default (and so that line numbers are still accurate); but -I cannot be
changed semantics to match that new option.

I'm closing this report as we are matching our documentation, although
we can reopen it if someone is interested in writing a patch for such a
new option.

> *The information transmitted is intended only for the person or entity to

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-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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