Shell Programming and Scripting

#!/usr/bin/env bash

set +m -f
shopt -s lastpipe

f() {
    local -i x y                   # Store each character in $x. $y is just a counter.
    while read -rN1 "x[y++]"; do
        printf '%d ' "${1}" >&2    # keep track of which job this is.
    done
    printf "${#x[@]} "             # Print the total number of reads by each job.
}

g() {
    f 1 <${1} &
    f 2 <${1}
}

declare -i ex=1

echo "example $((ex++)):"
# This works as I expect, f is backgrounded and two readers of one pipe each get about half the input:

read -ra x < <({ f 1 & f 2; } < <(printf '%.s0' {0..20}))
printf '%b\n' "\n${x[@]}\n"

echo "example $((ex++)):"
# In this equivalent version, f is not backgrounded, and one reader consumes all of the input, I can only assume for some reason because it's part of a pipeline:

{ f 1 & f 2; } < <(printf "%.s0" {0..20}) | {
    read -ra x
    printf '%b\n' "\n${x[@]}\n"
}

echo "example $((ex++)):"
# Same as above. Unsafe wordsplitting for brevity.

printf '%s\n' $'\n'$(printf '%.s0' {0..20} | { f 1 & f 2; })

printf '\n%s\n' "example $((ex++)):"
# Identical to the above two examples, except rather than using the command group's stdin, save the FD to $x and redirect individually. Now it behaves as the first example again. (WTF???)

{ f 1 <&${x} & f 2 <&${x}; } {x}< <(printf "%.s0" {0..20}) | {
    read -ra x
    printf '%b\n' "\n${x[@]}\n"
}

echo "example $((ex++)):"
# In this version, the name of the pipe is passed to g and then individually redirected to f, but it doesn't work. No matter how much data it gets, the pipe is closed before the second call to f sees it:

read -ra x < <(g <(printf "%.s0" {0..20}))
printf '%b\n' "\n${x[@]}\n"
wait

# vim: set fenc=utf-8 ff=unix ts=4 sts=4 sw=4 ft=sh nowrap et:

 $ ./pipefork 
example 1:
2 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 2 1 2 2 1 
13
10

example 2:
2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 
1
22

example 3:
2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
1
22

example 4:
2 1 2 1 2 1 2 1 2 1 1 2 1 1 2 1 1 2 1 2 1 
10
13

example 5:
1 1 ./pipefork: line 16: /dev/fd/63: No such file or directory
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 
22

..............
g() {
exec 4<${1}
f 1 <${1} &
f 2 <&4
}
...............
.........