[jrockway]

Even more fun is that if you create /dev/udp/127.0.0.1 (and chmod a+rwx), it won't create the file 53 if you "echo hello > /dev/udp/127.0.0.1/53". Instead it sends a UDP packet to your DNS server.

If you create a symlink to a path like /dev/udp/127.0.0.1/53 and redirect output to the symlink, a packet is not sent; the file is written as normal.

I'm guessing nobody has ever actually had a problem with this, so it's not actually a bad design choice, but I personally wouldn't have written that code. Leaky abstraction.

[zeroimpl]

I dunno, if you “echo foo > /dev/null” then “cat /dev/null” you won’t get foo back. Plenty of assumptions about filesystem behaviour don’t work in all cases.

That being said, I’d prefer if the symlink actually worked and sent the packet.

[jrockway]

Yeah when I was testing it, I definitely half-expected the symlink to work.

I will quibble with you on /dev/null a little bit. /dev/null works like any other file; there is absolutely no guarantee that you can read what you wrote on any filesystem write on UNIX. You can "echo foo > regular_file" and then "cat regular_file" and it could be gone or have completely different content. Other processes writing the file, network filesystems, quantum rays, who knows. So to me, /dev/null is not unusual in that respect at all, except that that probability function that you can read what you wrote looks a little different than a regular file.

Most importantly, /dev/null isn't a construction implemented by bash. Any program on the OS sees the same behavior as your shell script. That said, this isn't really as unusual as I originally thought. You can open a file named $HOME/foo in bash and that's going to be a very different file in your C program. I do like the $ to indicate "hey this is a quirk of the programming language that's allowing this", though.

[elteto]

That’s probably because bash is only looking for those types of paths in a redirection context. But if you try to use regular file utilities those paths don’t have any special meaning so they just work as normal.