Following a blog, I created a batch file, wm.bat:
\"d:\\svnroot\\external\\winmerge\\WinMerge.exe\" /B /WAIT \"d:\\svnroot\\external\\winmerge\\WinMergeU.exe
For Mac::
open this file : ~/.subversion/config
find and uncomment line containing : diff-cmd ( by removing # from start )
in front of diff-cmd, give the name of the diff tool, like in my case i was using araxis merge diff tool, so it looked like this :
diff-cmd=/Applications/Araxis Merge.app/Contents/Utilities/araxissvndiff
After this whenever you will run svn diff on terminal, if will show difference of the files in that tool
make sure there is no space before and after diff-cmd word.