[bug-diffutils] [PATCH] Add --ed-line-numbers-only option to diff

[Niklas Hambüchen]

Hello,

in a recent file system failure, I lost quite a bit of work on Gtk, so I 
wrote a program that helps finding lost file names (e.g. as a result of 
a system recovery like extundelete) by comparing them to similar files.

To calculate the similarity of files, I compare the number of common 
lines between to files to their sizes. To find that number of common 
lines, I use (ah, finally...) diff.

I found it quite interesting that I had to spend hours searching for a 
program to just tell how many lines of two files are the same, or more 
generally, to tell me which parts of two files are the same and where 
exactly additions, deletions and replacements are.

After some time, I finally found the diff -e flag, that prints out the 
ed (ed is the standard editor!) commands to transform the one file into 
the other. This information can nicely be used to calculate all these 
things (it indeed already prints out additions, deletions and 
replacements in a line-based fashion, so that only the similar hunks 
have to be calculated off that data).
However, it also prints out the actual file (change) content, which is a 
mess to parse, even more if you are not interested in the result.

I therefore propose the following patch that implements a 
--ed-line-numbers-only option to omit the contents and only print out 
the difference location information.

Thank you
Niklas