Simple line count program using POSIX file APIs.

linecount.c

#include <stdio.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/uio.h>
#include <unistd.h>

void count_lines(char* filename)
{
    int fd;
    int s;
    int i;
    int lines = 0;
    static char buf[32768];

    fd = open(filename, O_RDONLY);

    if(0 > fd)
    {
        perror(filename);
        return;
    }

    while(0 < (s = read(fd, &buf, sizeof(buf))))
    {
        for(i = 0 ; i < s ; i++)
        {
            if(buf[i] == '\n') lines++;
        }
    }

    close(fd);

    printf("%8d %s\n", lines, filename);
}

int main(int argc, char* argv[])
{
    int i = 1;

    if(argc < 2)
    {
        return 1;
    }

    for(; i < argc ; i++)
    {
        count_lines(argv[i]);
    }
}