On Mon, Nov 02, 2026 at 02:38:43PM +0100, Christian Schulte wrote:
> Do not use 'Z'. Use '%z'.

Sure... but let's save some space in case it is +0000. Maybe like so?

This changes the ts(1) default format to ISO8601.

Index: ts.1
===================================================================
RCS file: /cvs/src/usr.bin/ts/ts.1,v
diff -u -p -r1.8 ts.1
--- ts.1	3 Jul 2022 16:55:39 -0000	1.8
+++ ts.1	2 Nov 2026 14:48:34 -0000
@@ -52,7 +52,7 @@ specifications described in the
 .Xr strftime 3
 manual page.
 The default format is
-.Qq %b %d %H:%M:%S ;
+.Qq %Y-%m-%dT%H:%M:%S%z ;
 or
 .Qq %H:%M:%S
 if one of the
@@ -79,9 +79,9 @@ and
 .Qq 4:20:00.00001 .
 .Sh EXAMPLES
 .Bd -literal -offset indent
-$ (echo foo; sleep 2; echo bar) | ts
-Jun 28 12:13:38 foo
-Jun 28 12:13:40 bar
+$ (echo foo; sleep 2; echo bar) | TZ=Etc/UTC ts
+2026-11-02T14:24:50Z foo
+2026-11-02T14:24:52Z bar
 
 $ ls | ts -i %.S
 00.000452 CVS
Index: ts.c
===================================================================
RCS file: /cvs/src/usr.bin/ts/ts.c,v
diff -u -p -r1.11 ts.c
--- ts.c	11 Oct 2022 07:36:27 -0000	1.11
+++ ts.c	2 Nov 2026 14:48:34 -0000
@@ -34,7 +34,7 @@ struct usec {
 	char *pos;
 };
 
-static char		*format = "%b %d %H:%M:%S";
+static char		*format;
 static char		*buf;
 static char		*outbuf;
 static size_t		 bufsize;
@@ -44,6 +44,17 @@ static void		 fmtfmt(void);
 static void		 fmtprint(const struct timespec *);
 static void __dead	 usage(void);
 
+static int
+localtz_is_utc(void)
+{
+	time_t now;
+	struct tm *local;
+
+	now = time(NULL);
+	local = localtime(&now);
+	return local->tm_gmtoff == 0;
+}
+
 int
 main(int argc, char *argv[])
 {
@@ -87,6 +98,12 @@ main(int argc, char *argv[])
 
 	if (argc == 1)
 		format = *argv;
+	else {
+		if (localtz_is_utc())
+			format = "%Y-%m-%dT%H:%M:%SZ";
+		else
+			format = "%Y-%m-%dT%H:%M:%S%z";
+	}
 
 	bufsize = strlen(format) + 1;
 	if (bufsize > SIZE_MAX / 10)