shell interview problems

nonsense.sh

# from a file print 10 lines that are directly before the last ten lines without using tail or head
{ tac | while read l; do [ "${i:=0}" -lt 20 -a "$i" -ge 10 ] && echo "$l"; i=$(($i + 1)); done | tac; } < file

# monitor changes to a file without using tail -f
while : ; do read line && echo "$line" || sleep 1; done < file