who.c

来自「操作系统源代码」· C语言 代码 · 共 72 行

/*	who 1.5 - tell who is currently logged in	Author: Kees J. Bot
 *								9 Jul 1989
 */
#define nil 0
#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/stat.h>
#include <utmp.h>
#include <time.h>
#include <string.h>

char PATH_UTMP[] = "/etc/utmp";

char day[] = "SunMonTueWedThuFriSat";
char month[] = "JanFebMarAprMayJunJulAugSepOctNovDec";

int main(int argc, char **argv)
{
	char *tmp= PATH_UTMP;
	FILE *f;
	struct utmp ut;
	struct tm *tm;
	int slot, wtmp= 0, once= 0;

	if (argc > 3) {
		fprintf(stderr, "Usage: who <account-file>  |  who am i\n");
		exit(1);
	}
	if (argc == 2) {
		tmp= argv[1];
		wtmp= 1;
	}

	if ((f= fopen(tmp, "r")) == nil) {
		fprintf(stderr, "who: can't open %s\n", tmp);
		exit(1);
	}
	if (argc == 3) {
		if ((slot= ttyslot()) < 0) {
			fprintf(stderr, "who: no access to terminal.\n");
			exit(1);
		}
		fseek(f, (off_t) sizeof(ut) * slot, 0);
		once= 1;
	}

	while (fread((char *) &ut, sizeof(ut), 1, f) == 1) {
		if (!wtmp && ut.ut_name[0] == 0) continue;

		tm= localtime(&ut.ut_time);

		printf("%-9.8s %-9.8s %.3s %.3s %2d %02d:%02d",
			ut.ut_name,
			ut.ut_line,
			day + (3 * tm->tm_wday),
			month + (3 * tm->tm_mon),
			tm->tm_mday,
			tm->tm_hour,
			tm->tm_min
		);

		if (ut.ut_host[0] != 0) printf("  (%.*s)",
				(int) sizeof(ut.ut_host), ut.ut_host);

		printf("\n");
		if (once) break;
	}
	exit(0);
}