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  • Yea the sudo ruby <(echo "puts 'hello'") doesn't work. It is from this answer. The only way it worked was the way I had it in my question. I was going for a one-liner Commented Apr 16, 2021 at 22:45
  • So you're saying that if I do something like exec 1>&7-, bash will simply parse this to mean "close fd 1", and just ignores the 7 in there? But without the -, it means, redirect fd 1 to fd 7? Seems like quite the jump in reasoning, but I guess it makes sense Commented Apr 16, 2021 at 22:47
  • 1
    @smac89, oooh, right, it's /proc/$$/fd/, not /proc/self/fd/, so you're letting ruby "steal" the fd from the shell's fd list. That's... somewhat convoluted, but ok, I suppose it works. Commented Apr 16, 2021 at 22:50
  • @smac89 1>&7 would mean to fd 1 a copy of fd 7. 1>&- would close fd 1. I'm not at all sure what 1>&7- should be. Oh, should have read the manual, it moves the fd from 7 to 1. Commented Apr 16, 2021 at 22:52
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    @smac89, not quite that either. Let's take something similar to the first one. exec {ec}< <(echo "echo bye"). Say ec gets the number 9, just to pick one. Now, fd 9 is connected to the process substitution. Now, don't do anything else with $ec, just run the exec <&$ec-, same as exec 1<&9-. That says to move 9 to 1 (stdin), so now 1 is connected to the process substitution and 9 gets closed. Then the shell reads input from 1, now the process substitution. It reads echo bye, runs that, gets an end-of-file, and exits. Commented Apr 16, 2021 at 23:07