how to convert from one date format to another format in linux ?

 how to convert from one date format to another format in linux ?

echo 04-11-2021 | { IFS=- read d m y && echo "$y$m$d"; }

20211104

echo 04-11-2021 | { IFS=- read d m y && echo "$y/$m/$d"; }

2021/11/04

 echo 04-11-2021 | { IFS=- read d m y && echo "$d$m$y"; }

04112021

 echo 04-11-2021 | awk -F- '{print $3$2$1}'

20211104

echo 04-11-2021 |gawk -F, '{split($1, a, "-"); print a[3] a[2] a[1]}' 

20211104

echo 04/11/2021 | { IFS=/ read d m y && echo "$y$m$d"; }

20211104

date -d "20211104" "+%Y-%m-%d"

2021-11-04

date -d 04/11/2021 +%F

2021-04-11

 %F   full date; same as %Y-%m-%d