How can I diff 2 files while ignoring leading white space

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.