utils

date.c (2043B)

// Collection of Unix tools, comparable to coreutils
// SPDX-FileCopyrightText: 2017-2022 Haelwenn (lanodan) Monnier <contact+utils@hacktivis.me>
// SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only
#define _POSIX_C_SOURCE 200809L
#include <errno.h>  /* errno */
#include <locale.h> /* setlocale() */
#include <stdio.h>  /* BUFSIZ, perror(), puts() */
#include <stdlib.h> /* exit(), strtol() */
#include <time.h>   /* time, localtime, tm, strftime */
#include <unistd.h> /* getopt(), optarg, optind */
int
custom_datetime(time_t *now, char *optarg)
{
	if(optarg[0] == '@')
	{
		optarg++;
		errno = 0;
		*now  = (time_t)strtol(optarg, NULL, 10);
		if(errno != 0)
		{
			perror("strtol");
			return 0;
		}
		return 1;
	}
	return 0;
}
void
usage()
{
	fprintf(stderr, "date [-u][-d datetime] [+format]\n");
}
int
main(int argc, char *argv[])
{
	char outstr[BUFSIZ];
	struct tm *tm;
	time_t now;
	char *format = "%c";
	int uflag    = 0;
	int c;
	setlocale(LC_ALL, "");
	now = time(NULL);
	if(now == (time_t)-1)
	{
		perror("time");
		exit(EXIT_FAILURE);
	}
	while((c = getopt(argc, argv, ":d:u")) != -1)
	{
		switch(c)
		{
		case 'd': /* Custom datetime */
			if(!custom_datetime(&now, optarg))
			{
				return 1;
			}
			break;
		case 'u': /* UTC timezone */
			uflag++;
			break;
		case ':':
			fprintf(stderr, "Error: Missing operand for option: '-%c'\n", optopt);
			usage();
			return 1;
		case '?':
			fprintf(stderr, "Error: Unrecognised option: '-%c'\n", optopt);
			usage();
			return 1;
		}
	}
	if(uflag)
	{
		tm = gmtime(&now);
		if(tm == NULL)
		{
			perror("gmtime");
			exit(EXIT_FAILURE);
		}
	}
	else
	{
		tm = localtime(&now);
		if(tm == NULL)
		{
			perror("localtime");
			exit(EXIT_FAILURE);
		}
	}
	argc -= optind;
	argv += optind;
	(void)argc;
	if(*argv && **argv == '+') format = *argv + 1;
	errno = 0;
	if(strftime(outstr, sizeof(outstr), format, tm) == 0 && errno != 0)
	{
		perror("strftime");
		exit(EXIT_FAILURE);
	}
	if(puts(outstr) < 0)
	{
		perror("puts");
		exit(EXIT_FAILURE);
	}
	return 0;
}