how can I diff two sections of the same file?

Question

I have a source file with two similar yet subtly different sections. I'd like to merge the two sections into one subroutine with a parameter that handles the subtle differences, but I need to be sure I'm aware of them all so I don't miss any.
What I usually do in such cases is copy each of the sections to a separate file and then use tkdiff or vimdiff to highlight the differences. Is there any way to skip the intermediate files and just diff two parts of the same file?

Answer 1

i chose to rework @ordnungswidrig's answer into a bash function (i was only interested in the differences from a single file, but this could easily be changed to handle two different files...):

# find differences within a file giving start and end lines for both sections
function diff_sections {
  local fname=`basename $1`;
  local tempfile=`mktemp -t $fname`;
  head -$3 $1 | tail +$2 > $tempfile && head -$5 $1 | tail +$4 | diff -u $tempfile - ;
  rm $tempfile;
}

you call the function like so... diff_sections path/to/file 464 483 485 506

Answer 2

The linediff plugin for Vim works well for me. Visually select one section of your file and type :Linediff. Visually select the other section and type :Linediff. It will put vim in to vimdiff mode, showing only the two sections you highlighted previously. Type:LinediffReset to exit vimdiff mode.

More info:

https://unix.stackexchange.com/a/52759/32477

https://superuser.com/a/414958/199800