little-things/parent-urls

#!/bin/bash
prog0='BEGIN { FS="/"; OFS="/" }' # Set the field separators
prog1='{ print }' # Print the input URL (if desired)
prog2='/\/$/ { --NF }' # Remove the trailing blank field if the URL ends with a slash
prog3='{ for (i = NF; i > 3; --i) { --NF; print $0 OFS; } }' # One by one, remove the last path component, print remaining fields

prog="${prog0}  "
if [[ "$1" == '--with-original' ]]
then
	prog="${prog}${prog1}  "
fi
prog="${prog}${prog2}  ${prog3}"

exec awk "${prog}"