psub does not allow cooperative multitasking

[kwaze]

In your Bash prompt enter less -f <(yes | awk '{print NR}'). Compare that to less (yes | awk '{print NR}' | psub) in Fish which makes the shell freeze.

[kwaze]

The following works.
Using named pipes:

 mkfifo numbers.fifo
 yes | awk '{print NR}' > numbers.fifo&
 less numbers.fifo

and when you exit less, do

  rm numbers.fifo

Maybe psub could be changed to work that way?

[faho]

That works. Maybe psub could be changed to work that way?

That's what psub is supposed to do unless invoked with the "-f"/"--file" option, but there's a bug. Try again with a17b9fd.

[faho]

Oh, we actually already have a bug about this: #1040. Closing this as a duplicate.

[geoff-nixon]

Actually, this is isn't #1040, its much more along the lines of #238 - #563 - #1396.
Basically, bash forks at all command and process substitutions, fish does not.

Using your example @kwaze, we can reproduce the same issue without sub with something like:

mkfifo numbers.fifo
function yesawk
  yes | awk '{print NR}'
end
yesawk > numbers.fifo &
... # hang

Which is definitely a big annoying fish bug. However, for your particular case, why is

yes | awk '{print NR}' | less -f

insufficient? Process substitution is always icky, even in other shells. Its all about the pipeline! 😉

[faho]

Actually, this is isn't #1040, its much more along the lines of #238 - #563 - #1396.

Some combination of those as applied to psub is this and 1040.