How to do nothing forever in an elegant way?

I don't think you're going to get any more elegant than the

tail -f /dev/null

that you already suggested (assuming this uses inotify internally, there should be no polling or wakeups, so other than being odd looking, it should be sufficient).

You need a utility that will run indefinitely, will keep its stdout open, but won't actually write anything to stdout, and won't exit when its stdin is closed. Something like yes actually writes to stdout. cat will exit when its stdin is closed (or whatever you re-direct into it is done). I think sleep 1000000000d might work, but the tail is clearly better. My Debian box has a tailf that shortens command slightly.

Taking a different tack, how about running the program under screen?

sleep infinity is the clearest solution I know of.

You can use infinity because sleep accepts a floating point number*, which may be decimal, hexadecimal, infinity, or NaN, according to man strtod.

* This isn't part of the POSIX standard, so isn't as portable as tail -f /dev/null. However, it is supported in GNU coreutils (Linux) and BSD (used on Mac) (apparently not supported on newer versions of Mac — see comments).

sleep 2147483647 | program > output &

Yes, 2^31-1 is a finite number, and it won't run forever, but I'll give you $1000 when the sleep finally times out. (Hint: one of us will be dead by then.)

• no temporary files; check.
• no busy-waiting or periodic wakeups; check
• no exotic utilities; check.
• as short as possible. Okay, it could be shorter.