grep -w -e '(.)(.).21' file
grep --label=foo something
cat /var/log/apache/access_log | grep 404
grep -H 'eli' /etc/passwd
grep -r 'hello' /home/gigi
grep --color=always -iw lm /proc/cpuinfo
grep -E -e '^(.?)(.?)(.?)(.?)(.?)(.?)(.?)(.?)(.?).?987654321$' file
cat /etc/passwd | grep root
grep -rH --include='*.c' 'hello' /home/gigi