why does this work? wtf

sed -e 's/([0-9]){4}/****/g2'

sed -E "s/([0-9]{4} ){3}/** ** **** /g" expl: ([0-9]{4}) tells sed that find group of 4 digits and {3} tells no of groups , so we are capturing 3 groups of 4-digits and replaces them with *

^ -> from the start

cat | sed 's/^............../**** **** ****/'

I used awk

awk '{$1="****"; $2="****"; $3="****"; print $1, $2, $3, $4}' 

if someone can tell me how to use sed I'm beginner