Diffident – command line side-by-side diff editor

I really like Beyond Compare, which is a proprietary diff program with all those little touches that make it a joy to use*. The way I write code at work generally involves a bit of hacking in jEdit, checking the code myself, and then reviewing the code with a colleague.

*Recently, though, they’ve brought out a newer version that seems to overcomplicate things.

Both my own checking and the code review with a colleague generally involve comparing the code with the previous version in the (perforce) repository. Beyond Compare integrates nicely with the perforce tools and allows you to see a change as diffs of each file involved.

None of this is anything new to the Free Software world, of course. All the version control programs I’ve used allow you to do the equivalent of cvs diff and see what changes you’ve made. Git has a particularly good git diff mode which by default colours your diff and pipes it to less, making it easy to read and use.

What I have found myself missing recently, though, is the ability to edit the files as you diff them. The whole point of reviewing what you’ve done is to make changes as they occur to you, and with perforce + Beyond Compare it is really natural to make those changes within the diff tool.

Incidentally, I also really like the side-by-side style of Beyond Compare. By default it inserts “missing” lines so that all the similar lines are aligned, rather than trying to indicate with balloon-like lines that code has been inserted or transformed. I find those balloons very annoying and confusing (and they take up space on my screen, grr).

Having a side-by-side view also makes copying lines from one side to the other much easier. I often copy from one side to the other – especially when I realise what I have done is stupid and I want to revert a section back to how it was.

So, to curtail an already-long story, I decided there was yet another area of my life where the only solution was to run software I had written, rather than relying on the shoddy stuff put out by others, so I wrote a diff tool.

Diffident is a diff tool inspired by Beyond Compare and git. It shows you a side-by-side diff of your files in a terminal (one day it may have a GTK+ interface too) and allows you to edit them. The editing part is in development – expect a release fairly soon, or get the code from the git repository. The output is coloured, and you can see the whole of both files, using keyboard shortcuts to jump to the next and previous differences.

You might ask “Why not just use Beyond Compare?” For a number of reasons:

1. It is not Free Software. I can’t improve it or trust it.
2. It’s sort of Windows-y. I know there is a Linux version, but I bet it’s not very Linux-y. (Disclaimer: I’ve never tried it ;)
3. It doesn’t work in a terminal.
4. The inline editing support is not great. Its real strength is copying from side to side.
5. It doesn’t feel right when used with git. I have got this set up in my Cygwin environment – it works, but it’s no fun.
6. It isn’t written by me.

I’d really like Diffident to become the de-facto diff tool for git people (and everyone else). That proves to be a bit trickier than I’d like because of the way git interacts with diff tools, but I’ve got a decent solution for using it as the GIT_EXTERNAL_DIFF tool, and I hope to improve it in the future. (For those who are interested, the kind of thing I’m thinking about is how to get git diff --cached to allow me to edit the files in the index.)

So anyway, check out Diffident and if you like it, help me make it better.