GNU bug report logs - #55652
please elaborate on diff -u -I RE

Previous Next

Full log

View this message in rfc822 format

From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#55652: closed (please elaborate on diff -u -I RE)
Date: Fri, 27 May 2022 01:54:02 +0000

[Message part 1 (text/plain, inline)]

Your message dated Thu, 26 May 2022 18:53:20 -0700
with message-id <67d65b7a-1438-9033-e331-6791bc0043f8 <at> cs.ucla.edu>
and subject line Re: [bug-diffutils] bug#55652: please elaborate on diff -u -I RE
has caused the debbugs.gnu.org bug report #55652,
regarding please elaborate on diff -u -I RE
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


-- 
55652: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=55652
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

[Message part 2 (message/rfc822, inline)]

From: Harald Dunkel <harri <at> afaics.de>
To: bug-diffutils <at> gnu.org
Subject: please elaborate on diff -u -I RE
Date: Thu, 26 May 2022 11:15:39 +0200

Hi folks,

I have hoped that

	diff -I '^[[:space:]]*\#' file1 file2

would ignore comment lines, but it doesn't work as I expected.
Example:

	#!/bin/bash

	diff -version | head -1

	echo -e '\t# comment 1' >/tmp/x1
	echo -e '\t# comment 2' >/tmp/x2
	diff -u -I '^[[:space:]]*\#' /tmp/x1 /tmp/x2 && echo 'no diffs'

	echo -e '' >>/tmp/x1
	echo -e '' >>/tmp/x2
	diff -u -I '^[[:space:]]*\#' /tmp/x1 /tmp/x2 && echo 'still no diffs'

	echo -e 'hello, world' >>/tmp/x2
	diff -u -I '^[[:space:]]*\#' /tmp/x1 /tmp/x2 && echo 'no diffs'
	echo "diff --normal"
	diff -I '^[[:space:]]*\#' /tmp/x1 /tmp/x2 && echo 'no diffs'

Output:

	diff (GNU diffutils) 3.8
	no diffs
	still no diffs
	--- /tmp/x1     2022-05-26 10:54:36.187361365 +0200
	+++ /tmp/x2     2022-05-26 10:54:36.191361276 +0200
	@@ -1,2 +1,3 @@
	-       # comment 1
	+       # comment 2
	
	+hello, world
	diff --normal
	2a3
	> hello, world

This seems weird. Only 1 line has been appended to x2 before running
diff the third time. It does not match the pattern. How comes diff -u
reports 2 different lines, with an unchanged line in between? Is this
as expected?


Regards

Harri

[Message part 3 (message/rfc822, inline)]

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Harald Dunkel <harri <at> afaics.de>
Cc: 55652-done <at> debbugs.gnu.org
Subject: Re: [bug-diffutils] bug#55652: please elaborate on diff -u -I RE
Date: Thu, 26 May 2022 18:53:20 -0700

On 5/26/22 02:15, Harald Dunkel wrote:
> How comes diff -u
> reports 2 different lines, with an unchanged line in between?

What else can diff do? You asked for context, and the context lines differ.


> Is this
> as expected? 

Yes, the manual says:

   However, '-I' only ignores the insertion or deletion of lines that
contain the regular expression if every changed line in the hunk--every
insertion and every deletion--matches the regular expression.  In other
words, for each nonignorable change, 'diff' prints the complete set of
changes in its vicinity, including the ignorable ones.


One might add an option to make diff behave differently in this case, 
although it's not clear what the "right" behavior would be. In the 
meantime perhaps you can get by with "diff -U0 -Iwhatever".

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.