source: vendor/bash/3.1-p17/examples/functions/coproc.bash

# coprocess.bash
#
# vi:set sts=2 sw=2 ai:
#

coprocess_pid=

#
# coprocess - Start, control, and end coprocesses.
#
function coprocess ()
{
  while (( $# > 0 )) ; do
    case "$1" in
      #
      # coprocess close
      #
      c|cl|clo|clos|close)
        shift
        exec 61>&- 62<&-
        coprocess_pid=
        if [ "$1" = "-SIGPIPE" ] ; then
          # Only print message in an interactive shell
          case "$-" in
            *i*)
              echo 'SIGPIPE' >&2
              ;;
          esac
          return 1
        fi
        return 0
        ;;

      #
      # coprocess open
      #
      o|op|ope|open)
        shift
        local fifo="/var/tmp/coprocess.$$.$RANDOM"

        local cmd="/bin/bash"
        if (( $# > 0 )) ; then
          cmd="$@"
        fi

        mkfifo "$fifo.in" || return $?
        mkfifo "$fifo.out" || {
          ret=$?
          rm -f "$fifo.in"
          return $?
        }

        ( "$@" <$fifo.in >$fifo.out ; rm -f "$fifo.in" "$fifo.out" ) &
        coprocess_pid=$!
        exec 61>$fifo.in 62<$fifo.out
        return 0
        ;;

      #
      # coprocess print - write to the coprocess
      #
      p|pr|pri|prin|print)
        shift
        local old_trap=$(trap -p SIGPIPE)
        trap 'coprocess close -SIGPIPE' SIGPIPE
        if [ $# -eq 1 ] && [ "$1" = "--stdin" ] ; then
          cat >&61
        else
          echo "$@" >&61
        fi
        local ret=$?
        eval "$old_trap"
        return $ret
        ;;

      #
      # coprocess read - read from the coprocess
      #
      r|re|rea|read)
        shift
        local old_trap=$(trap -p SIGPIPE)
        trap '_coprocess_close -SIGPIPE' SIGPIPE
        builtin read "$@" <&62
        local ret=$?
        eval "$old_trap"
        return $ret
        ;;

      s|st|sta|stat|statu|status)
        if [ -z "$coprocess_pid" ] ; then
          echo 'no active coprocess'
          return 1
        else
          echo "  coprocess is active [$coprocess_pid]"
          return 0
        fi
        ;;

      *)
        coprocess print "$@"
        return $?
        ;;
    esac
    shift
  done
  coprocess status
  return $?
}