59 lines
1.2 KiB
C
59 lines
1.2 KiB
C
|
#define _GNU_SOURCE
|
||
|
|
#include <stdbool.h>
|
||
|
|
#include <stdio.h>
|
||
|
|
#include <stdlib.h>
|
||
|
|
#include <unistd.h>
|
||
|
|
|
||
|
|
// You may assume that lines are no longer than 1024 bytes
|
||
|
|
#define LINELEN 1024
|
||
|
|
|
||
|
|
static void usage (void) __attribute__ ((unused));
|
||
|
|
|
||
|
|
int
|
||
|
|
main (int argc, char *argv[])
|
||
|
|
{
|
||
|
|
int opt;
|
||
|
|
int n = 5;
|
||
|
|
|
||
|
|
while ((opt = getopt (argc, argv, "n:")) != -1)
|
||
|
|
{
|
||
|
|
switch (opt)
|
||
|
|
{
|
||
|
|
case 'n':
|
||
|
|
n = strtol (optarg, NULL, 10);
|
||
|
|
break;
|
||
|
|
default:
|
||
|
|
printf ("./bin/head: invalid option -- \'%c\'\n", optopt);
|
||
|
|
exit (EXIT_FAILURE);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
FILE *file = optind < argc ? fopen (argv[optind], "r") : stdin;
|
||
|
|
if (file == NULL)
|
||
|
|
{
|
||
|
|
perror ("Failed to open input file");
|
||
|
|
exit (EXIT_FAILURE);
|
||
|
|
}
|
||
|
|
|
||
|
|
char buffer[LINELEN];
|
||
|
|
int count = 0;
|
||
|
|
|
||
|
|
while (count < n && fgets (buffer, sizeof (buffer), file) != NULL)
|
||
|
|
{
|
||
|
|
printf ("%s", buffer);
|
||
|
|
count++;
|
||
|
|
}
|
||
|
|
|
||
|
|
return EXIT_SUCCESS;
|
||
|
|
}
|
||
|
|
|
||
|
|
static void
|
||
|
|
usage (void)
|
||
|
|
{
|
||
|
|
printf ("head, prints the first few lines of a file\n");
|
||
|
|
printf ("usage: head [FLAG] FILE\n");
|
||
|
|
printf ("FLAG can be:\n");
|
||
|
|
printf (" -n N show the first N lines (default 5)\n");
|
||
|
|
printf ("If no FILE specified, read from STDIN\n");
|
||
|
|
}
|