head

Keep only 10 first lines:

seq 20 | head

Keep only 2 first lines:

[ "$(printf '1\n2\n3\n4\n' | head -n2)" = "$(printf '1\n2\n')" ] || exit 1

2 first bytes:

[ "$(echo -en 'abc' | head -c 2)" = 'ab' ] || exit 1

GNU extensions

Remove last two bytes:

[ "$(echo -en 'abc' | head -c -2)" = 'a' ] || exit 1