cmb_test2.sh

#!/bin/sh
dpv(){ command dpv -k -b "$0" -p "$items\n" -t "$*" -a "\nCombinations:" \
    -l "$total: "; }
items="a b c d e f g h i j k l m n o p q r s t u v w x y z"
total=$( cmb -t $items )
start=$( date +%s )
trap exit SIGINT
clear
cmb $items | dpv cmb
end=$( date +%s )
elapsed1=$(( $end - $start ))
sixth=$(( $total / 6 ))
export items
start=$( date +%s )
time echo \
    :$sixth \
    $(( $sixth + 1 )):$sixth \
    $(( $sixth * 2 + 1 )):$sixth \
    $(( $sixth * 3 + 1 )):$sixth \
    $(( $sixth * 4 + 1 )):$sixth \
    $(( $sixth * 5 + 1 )): \
    | xargs -P6 -n1 sh -c '
        start=${1%%:*} count=${1#*:}
        cmb ${start:+-i$start} ${count:+-c$count} $items
    ' sh | dpv "xargs -P6 cmb"
end=$( date +%s )
elapsed2=$(( $end - $start ))
echo
awk -v e1=$elapsed1 -v e2=$elapsed2 'BEGIN {
    printf "cmb: %us   xargs: %us   opt: %.2fx\n", e1, e2, e1 / e2
}'