bug#55652: closed (please elaborate on diff -u -I RE)

[GNU bug Tracking System]

Your message dated Thu, 26 May 2022 18:53:20 -0700
with message-id <67d65b7a-1438-9033-e331-6791bc0043f8@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.

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-- 
55652: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=55652
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> --- Begin Message ---
>
>
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> Subject: 
>
> please elaborate on diff -u -I RE
>
>
>
>
> Date: 
>
> Thu, 26 May 2022 11:15:39 +0200
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>
>
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> User-agent: 
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> Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1
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>
>
>
> 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
>
>
>
> --- End Message ---
> --- Begin Message ---
>
>
>
> Subject: 
>
> Re: [bug-diffutils] bug#55652: please elaborate on diff -u -I RE
>
>
>
>
> Date: 
>
> Thu, 26 May 2022 18:53:20 -0700
>
>
>
>
> User-agent: 
>
> Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0
>
>
>
>
> 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".
>
>
> --- End Message ---