How can I diff 2 files while ignoring leading white space

Question

I have 2 source files, they are different versions of the same thing. However, one has been through a different editor that made indent changes, so all the lines are showing up different in diff.

Is there a diff command or a filter I can use to diff with so that the output will only be lines that are different after ignoring the leading spaces/tabs?

score 181 · Accepted Answer · answered May 07 '13 at 15:37

181

diff has some options that can be useful to you:

   -E, --ignore-tab-expansion
          ignore changes due to tab expansion

   -Z, --ignore-trailing-space
          ignore white space at line end

   -b, --ignore-space-change
          ignore changes in the amount of white space

   -w, --ignore-all-space
          ignore all white space

   -B, --ignore-blank-lines
          ignore changes whose lines are all blank

So diff -w old new should ignore all spaces and thus report only substantially different lines.

answered May 07 '13 at 15:37

Lev Levitsky

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It's worth noting that `-w` effectively removes all whitespace from the lines before comparing, so `ab` and `a b` are considered identical. I prefer `-b` because it ignores whitespace _changes_, meaning that `ab` and `a b` are considered different but `a b` and `a` + _multiple spaces_ + `b` (sorry, mini-Markdown wouldn't allow multiple spaces in code!) are considered the same. – IpsRich Oct 16 '15 at 07:56
How can I ignore all the newlines? – JobHunter69 Sep 29 '16 at 23:15
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Can I tell `diff` to ignore equivalent series expansions for transcendental numbers like e and pi? – geneorama Mar 27 '17 at 20:13
@RichardWiseman Good point; in cases when there is a mess of tab and space differences though, there's no good combination that works except `-w`. `-tb`, `-tbB` , `-t`, etc. all leak in some differences that you'd prefer to ignore. `-w` does not, even if it also might exclude some differences you'd prefer to see. – TurnipEntropy Apr 27 '18 at 17:29
@geneorama Yes, and you can ignore any change that does not alter the meaning of your program with the new `--ignore-goedel` option. – Elmar Zander Oct 10 '22 at 08:26
ignoring white space is cool and all.. except when comparing python code where white space is significant =) – horace Apr 24 '23 at 16:30

score 9 · Answer 2 · answered Sep 28 '17 at 16:38

diff -bB file[12]

-b, --ignore-space-change
      ignore changes in the amount of white space
-B, --ignore-blank-lines
      ignore changes whose lines are all blank

Please note that -w option will ignoring all whitespaces before diffing, so a line like this i s a line and this is a line in each file will compare as thisisaline and will not report differences.

Beside of -w option problem, even -b option has minor issues and that doesn't ignore whitespaces if come at the begging of a line

So you should use sed to remove those whitespaces occurred at start first then do `diff -bB.

diff -bB <(sed 's/^[ \t]*//' file1) <(sed 's/^[ \t]*//' file2)

score 1 · Answer 3 · answered May 07 '13 at 15:38

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If one is using tabs incorrectly, you can fix that

expand bad_file

answered May 07 '13 at 15:38

Zombo

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Chris Koknat · Answer 4 · 2020-09-22T22:12:55.107

My open-source Linux tool 'dif' compares files while ignoring various differences including whitespace.

It has many other options for ignoring comments or timestamps, sorting the input files, doing search/replace, ignoring certain lines, etc.

After preprocessing the input files, it runs the Linux tools meld, gvimdiff, tkdiff, or kompare on these intermediate files.

Installation is not required, just download and run the 'dif' executable from https://github.com/koknat/dif

To condense any whitespace to a single space, use the -white option:

dif file1 file2 -white

To remove all whitespace (except for newlines), use the -nowhite option:

dif file1 file2 -nowhite

How can I diff 2 files while ignoring leading white space

4 Answers4