Re: [hackers] [sbase][Patch] date: add date/time setting capability

From: John Vogel <jvogel4_AT_stny.rr.com>
Date: Wed, 28 Dec 2016 20:03:57 -0500

On Tue, 27 Dec 2016 17:34:02 -0800
Michael Forney <mforney_AT_mforney.org> wrote:

> One suggestion I can think of, since the date format is simple and
> uses fixed sizes, it to just parse into struct tm manually rather than
> restructuring the date string into a new buffer with spaces.
>
> For example (untested):
> static int date_field(char *s, size_t i) {
> return (s[i] - '0') * 10 + (s[i+1] - '0');
> }
>
> char *s = argv[0];
> tm->tm_mon = date_field(s, 0) - 1;
> tm->tm_day = date_field(s, 2);
> tm->tm_hour = date_field(s, 4);
> tm->tm_min = date_field(s, 6);
> switch (len) {
> case 8:
> tm->tm_year = now->tm_year;
> break;
> case 10:
> tm->tm_year = date_field(s, 8);
> if (tm->tm_year < 69)
> tm->tm_year += tm->year < 69 ? 2000 : 1900;
> break;
> case 12:
> tm->tm_year = date_field(s, 8) * 100 + date_field(s, 10);
> break;
> }
>

Thanks for the help, Michael. I made a couple adjustments to
account for tm_year needing to be 'years since 1900'. Tests
fine here.

--
 date.1 | 46 ++++++++++++++++++++++++++++++++++++++++++++--
 date.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++------
 2 files changed, 96 insertions(+), 8 deletions(-)
diff --git a/date.1 b/date.1
index 29081a5..0171936 100644
--- a/date.1
+++ b/date.1
_AT_@ -3,12 +3,15 @@
 .Os sbase
 .Sh NAME
 .Nm date
-.Nd print date and time
+.Nd print or set date and time
 .Sh SYNOPSIS
 .Nm
 .Op Fl d Ar time
 .Op Fl u
 .Op Cm + Ns Ar format
+.Sm off
+.Op Ar mmddHHMM Oo Oo Ar CC Oc Ar yy Oc
+.Sm on
 .Sh DESCRIPTION
 .Nm
 prints the date and time according to
_AT_@ -16,7 +19,8 @@ prints the date and time according to
 or
 .Ar format
 using
-.Xr strftime 3 .
+.Xr strftime 3
+or sets the date.
 .Sh OPTIONS
 .Bl -tag -width Ds
 .It Fl d Ar time
_AT_@ -27,6 +31,44 @@ Unix epoch 1970-01-01T00:00:00Z.
 .It Fl u
 Print UTC time instead of local time.
 .El
+.Pp
+An operand with a leading plus
+.Pq Cm +
+sign signals a user-defined format string using
+.Xr strftime 3
+conversion specifications.
+.Pp
+An operand without a leading plus sign is
+interpreted a value for setting the systems current date and time.
+The canonical representation for setting the date and time is:
+.Pp
+.Bl -tag -width Ds -compact -offset indent
+.It Ar mm
+The month of the year, from 01 to 12.
+.It Ar dd
+The day of the month, from 01 to 31.
+.It Ar HH
+The hour of the day, from 00 to 23.
+.It Ar MM
+The minute of the hour, from 00 to 59.
+.It Ar CC
+The first two digits of the year (the century).
+.It Ar yy
+The second two digits of the year.
+If
+.Ar yy
+is specified, but
+.Ar CC
+is not, a value for
+.Ar yy
+between 69 and 99 results in a
+.Ar CC
+value of 19. Otherwise, a
+.Ar CC
+value of 20 is used.
+.El
+.Pp
+The century and year are optional. The default is the current year.
 .Sh STANDARDS
 The
 .Nm
diff --git a/date.c b/date.c
index 1671e1f..4a18bd6 100644
--- a/date.c
+++ b/date.c
_AT_@ -1,6 +1,8 @@
 /* See LICENSE file for copyright and license details. */
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
+#include <errno.h>
 #include <time.h>
 
 #include "util.h"
_AT_@ -11,6 +13,11 @@ usage(void)
 	eprintf("usage: %s [-u] [-d time] [+format]\n", argv0);
 }
 
+static int date_field(const char *s, size_t i)
+{
+	return (s[i] - '0') * 10 + (s[i+1] - '0');
+}
+
 int
 main(int argc, char *argv[])
 {
_AT_@ -19,8 +26,6 @@ main(int argc, char *argv[])
 	time_t t;
 	char buf[BUFSIZ], *fmt = "%c", *tz = "local";
 
-	t = time(NULL);
-
 	ARGBEGIN {
 	case 'd':
 		t = estrtonum(EARGF(usage()), 0, LLONG_MAX);
_AT_@ -33,14 +38,55 @@ main(int argc, char *argv[])
 		usage();
 	} ARGEND
 
+	t = time(NULL);
+
+	if (!(now = tztime(&t)))
+		eprintf("%stime failed\n", tz);
+
 	if (argc) {
-		if (argc != 1 || argv[0][0] != '+')
+		if (argc != 1)
 			usage();
-		else
+		else if (argv[0][0] == '+') {
 			fmt = &argv[0][1];
+		}
+		else {
+			struct tm date;
+			struct timespec ts;
+
+			date.tm_mon = date_field(argv[0], 0) - 1;
+			date.tm_mday = date_field(argv[0], 2);
+			date.tm_hour = date_field(argv[0], 4);
+			date.tm_min = date_field(argv[0], 6);
+
+			switch (strlen(argv[0])) {
+			case 8:
+				date.tm_year = now->tm_year;
+				break;
+			case 10:
+				date.tm_year = date_field(argv[0], 8);
+				if (date.tm_year < 69)
+					date.tm_year += now->tm_year < 69 ? 0 : 100;
+				break;
+			case 12:
+				date.tm_year = ((date_field(argv[0], 8) - 19) * 100) + date_field(argv[0], 10);
+				break;
+			default:
+				eprintf("invalid date format: %s\n", argv[0]);
+			}
+			
+			t = mktime(&date);
+			if (t == (time_t)-1)
+				eprintf("mktime failed: bad calender date/time: %s\n", argv[0]);
+
+			ts.tv_sec = t;
+			ts.tv_nsec = 0;
+
+			if (clock_settime(CLOCK_REALTIME, &ts) == -1)
+				eprintf("clock_settime failed: %s\n", strerror(errno));
+
+			return fshut(stdout, "<stdout>");
+		}
 	}
-	if (!(now = tztime(&t)))
-		eprintf("%stime failed\n", tz);
 
 	strftime(buf, sizeof(buf), fmt, now);
 	puts(buf);

Received on Thu Dec 29 2016 - 02:03:57 CET