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#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int head(int fd, int lines, const char * name)
{
static const size_t SIZE = 1024 * 4;
char buffer[SIZE];
while (lines > 0) {
const ssize_t available = read(fd, buffer, SIZE);
if (-1 == available) {
perror(name);
return 1;
}
if (0 == available)
return 0;
size_t offset = 0;
for (ssize_t n = 0; n < available; ++n) {
if (buffer[n] == '\n') {
lines--;
if (0 <= lines) {
const ssize_t res = write(1, buffer + offset, 1 + n - offset);
if (-1 == res) {
perror(name);
return 1;
}
offset = 1 + n;
}
if (0 >= lines)
return 0;
}
}
if (0 < lines) {
const ssize_t res = write(1, buffer + offset, available - offset);
if (-1 == res) {
perror(name);
return 1;
}
}
}
return 0;
}
int main(int argc, char * argv[])
{
int opt;
int lines = 10;
while (-1 != (opt = getopt(argc, argv, "n:"))) {
switch (opt) {
case 'n':
errno = 0;
lines = strtol(optarg, (char **) NULL, 10);
if (lines < 0)
errno = EINVAL;
if (0 != errno) {
perror(optarg);
return 1;
}
break;
default:
dprintf(2, "Usage: %s [-n lines] [file...]\n", argv[0]);
return 1;
}
}
const unsigned int file_count = argc - optind;
int res = 0;
if (optind >= argc)
res |= head(0, lines, "-");
else for (int i = optind; i < argc; ++i) {
if (1 < file_count)
printf("==> %s <==\n", argv[i]);
const unsigned int is_stdin = '-' == argv[i][0] && 0 == argv[i][1];
const int fd = is_stdin ? 0 : open(argv[i], O_RDONLY);
if (-1 == fd) {
perror(argv[i]);
res = 1;
continue;
}
res |= head(fd, lines, argv[i]);
if (!is_stdin) {
const int clr = close(fd);
if (-1 == clr) {
perror(argv[i]);
res = 1;
}
}
}
return res;
}
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