Once head read enough bytes to satisfy -c option, it stops reading input and quit.

This is different from what -n does and it is also different from both FreeBSD and busybox head implementation.

With GNU Coreutils head:

$ echo -e "123\n456\n789" | { head -n 1; while read a; do echo "-$a-"; done; } 

123

$ echo -e "123\n456\n789" | { head -c 4; while read a; do echo "-$a-"; done; } 

123

-456-

-789-

$

With all other head implementations I tested:

$

It would make sense to both -n and -c have the same meaning, differing only whether to read bytes or lines.

Regards,