remember gnu parallel and / or xargs usage

gnu-parallel-xargs.md

(see: https://ryanmlayer.wordpress.com/2016/02/18/running-commands-in-parallel-with-xargs/)

#####GP

parallel '(head -1 f.bed ; grep -w ^{} f.bed | sort -nk 2) > f.{}.bed' ::: {1..22} X Y

#####xargs

echo -n $(seq 1 22) X Y | xargs -d ' ' -I{} -P 10
sh -c '(head -n1 f.bed; grep -w "^{}" f.bed | sort -n -k 2) > {}.f.bed'