#!/bin/bash
shopt -s extglob
export TIMEFORMAT="(%U + %S) / %R : %P  "

strings=(
    now snow '@0' '2009-02-13 23:31:30 UTC' '2001-09-09 01:46:40 UTC'
    'Sep 09 2001 UTC 01:46:39' 12:34:56 10/12 'Mar 25' 10:00 22:30 '7 Mon 12:00'
    'Apr 1 12:34' 'Dec 31 23:59' 'Jan 1 00:00' '@1' 'tomorrow' 'yesterday'
)
_sep=$'  :\n'

print2byLine() {
    printf "%-24s:%13s%s" "$1" "${2:(${#2}<14?0:${#2}-13)}" "${_sep%:*}"
    _sep="${_sep#*:}:${_sep%:*}"
}

multiforked() {
    local _string _out
    for _string in "${strings[@]}" ;do
	_out="$(date -d "$_string" +%s 2>&1)"
	print2byLine "$_string" "$_out"
    done
    printf "%-12s (%d dates): " ${FUNCNAME^^} ${#strings[@]} >&2
}
oldForked() {
    local _dateOut _dateIn _string _out _fifo=/tmp/fifo-demo-$$
    mkfifo $_fifo
    exec 9> >(exec stdbuf -o0 date -f - +%s >$_fifo 2>&1)
    exec 8<$_fifo
    rm $_fifo
    for _string in "${strings[@]}" ;do
	echo >&9 $_string
	read -t 1 -u 8 _out
	print2byLine "$_string" "$_out"
    done
    exec 8<&- 9>&-
    printf "%-12s (%d dates): " ${FUNCNAME^^} ${#strings[@]} >&2
}
forked() {
    local _dateOut _dateIn _string _out
    exec 8<> <(:)
    exec 9> >(exec stdbuf -o0 date -f - +%s >&8 2>&8)
    for _string in "${strings[@]}" ;do
	echo >&9 $_string
	read -t 1 -u 8 _out
	print2byLine "$_string" "$_out"
    done
    exec 8<&- 9>&-
    printf "%-12s (%d dates): " ${FUNCNAME^^} ${#strings[@]} >&2
}

time multiforked
time oldForked
time forked