how to make svn diff show only non-whitespace line changes between two revisions

You can use an alternate diff command using the --diff-cmd argument for svn diff. diff is a good utility that has plenty of features for ignoring whitespace.

For example:

svn diff --diff-cmd /usr/bin/diff -x "-w"

Use -x --ignore-space-change or -x --ignore-all-space. (See svn -h diff.)

Note that end-of-lines are not considered whitespace in this scenario and that has to be ignored with:

svn diff -x --ignore-eol-style [etc...]

You can use

svn diff -r 100:200 -x -b > file.diff

If you want to ignore all whitespaces:

svn diff -x -w | less

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