Re: assignment from background process

[Jesse Hathaway]

Another fun option, besides the ones Greg mentioned, is to use a bash coproc as
a background process and then use read with a timeout to poll the coproc for a
response. Below is a silly example of using a coproc to asynchronously send
gigabytes of data to devnull:

#!/bin/bash

copy_to_devnull_daemon() {
  read -r count
  if dd status=none if=/dev/zero of=/dev/null bs=1G count="${count}"; then
    printf 'SUCCESS: Copied %s gigs to /dev/null\n' "${count}"
  else
    printf 'ERROR: Unable to copy %s gigs to /dev/null\n' "${count}"
  fi
}

coproc copy_to_devnull { copy_to_devnull_daemon; }

COPY_TO_DEVNULL_OUT="${copy_to_devnull[0]}"
COPY_TO_DEVNULL_IN="${copy_to_devnull[1]}"

read_copy_to_devnull() {
  local timeout_secs
  timeout_secs=$1
  read -r -t "${timeout_secs}" reply <&"$COPY_TO_DEVNULL_OUT"
  printf '%s\n' "$reply"
}

write_copy_to_devnull() {
  local count
  count=$1
  printf '%s\n' "${count}" >&"$COPY_TO_DEVNULL_IN"
}

write_copy_to_devnull '50'

reply=""
while [[ $reply == "" ]]; do
  reply=$(read_copy_to_devnull 1)
done
printf 'Reply: "%s"\n' "${reply}"