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Subject: |
please elaborate on diff -u -I RE |
Date: |
Thu, 26 May 2022 11:15:39 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 |
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
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--- 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".
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