Show HN: rewrite, a rust-powered in-place file rewrite utility

So before anyone chimes in and asks why the title (or the OP) feels the need to point out that this was written in rust and perhaps any upvotes this submission has garnered are just from the rust fanclub.. you're right, I mostly wrote this in rust because of a desire to further familiarize myself with the language (it's been a year since I last used it).

However, I was going to write this anyway as it satisfies an itch I've had for a while. I had an implementation of `rewrite` as a bash script previously, but was not satisfied with it because I'm using `rewrite` in critical parts of my workflow and just don't trust bash the same way I do rust (or C/C++ or any other language, for that matter).

If you're also new to there are a few new things I've learned about rust that show up in the commit history (though not as much as I would have liked). In particular, using .expect() and .to_string_lossy() to avoid using .unwrap() directly (except where user input isn't a possible cause of failure). I had some try! code in there that was replaced by the new ? operator (not to be confused with the same operator in other languages like C#, the ? in rust is more of an inline try..catch rather than a null test/coalescing operator) but that code didn't even make the first commit.

There is also the "sponge" tool from Joey Hess' moreutils.

> You see, sort is too smart to read the entire file into memory, sort it, then spit it out on stdout, which is how it can manage sorting huge amounts of data without completely trashing your system memory.

This is not why the file is empty. sort doesn't need the original file for very long. Very likely it starts a merge sort by sorting smaller chunks of the input file to temporary files. As soon as all these initial-size chunks have been read, the input file is no longer needed.

The reason for the file being truncated is the semantics of I/O redirection:

    anyprogram somefile > somefile

means that the file is truncated by the shell (because of the redirection) before "anyprogram" even has the chance to open that file.