Recipe: Implementing head, tail, tac with awk

head
====

$ awk 'NR <=10' file


tail
====

$ awk '{ buffer[NR % 10] = $0; } END { for(i=1;i<11;i++) { print buffer[i%10] } }'

tac
===

$ awk '{ buffer[NR] = $0; } END { for(i=NR; i>0; i--) { print buffer[i] } }'