Reduce a difference with portable tmux by adding the -V flag and

#{version} format; on OpenBSD these just report the OpenBSD version.

format.c

@@ -1106,6 +1106,7 @@ format_create(struct client *c, struct cmdq_item *item, int tag, int flags)
 	ft->flags = flags;
 	ft->time = time(NULL);
 
+	format_add(ft, "version", "%s", getversion());
 	format_add_cb(ft, "host", format_cb_host);
 	format_add_cb(ft, "host_short", format_cb_host_short);
 	format_add_cb(ft, "pid", format_cb_pid);

proc.c

@@ -182,8 +182,8 @@ proc_start(const char *name)
 	if (uname(&u) < 0)
 		memset(&u, 0, sizeof u);
 
-	log_debug("%s started (%ld): socket %s, protocol %d", name,
+	log_debug("%s started (%ld): version %s, socket %s, protocol %d", name,
-	    (long)getpid(), socket_path, PROTOCOL_VERSION);
+	    (long)getpid(), getversion(), socket_path, PROTOCOL_VERSION);
 	log_debug("on %s %s %s; libevent %s (%s)", u.sysname, u.release,
 	    u.version, event_get_version(), event_get_method());
 

tmux.1

@@ -23,7 +23,7 @@
 .Sh SYNOPSIS
 .Nm tmux
 .Bk -words
-.Op Fl 2Cluv
+.Op Fl 2CluvV
 .Op Fl c Ar shell-command
 .Op Fl f Ar file
 .Op Fl L Ar socket-name
@@ -210,6 +210,11 @@ signal may be sent to the
 server process to toggle logging between on (as if
 .Fl v
 was given) and off.
+.It Fl V
+Report the
+.Nm
+version.
+.Pp
 .It Ar command Op Ar flags
 This specifies one of a set of commands used to control
 .Nm ,
@@ -4369,6 +4374,7 @@ The following variables are available, where appropriate:
 .It Li "session_windows" Ta "" Ta "Number of windows in session"
 .It Li "socket_path" Ta "" Ta "Server socket path"
 .It Li "start_time" Ta "" Ta "Server start time"
+.It Li "version" Ta "" Ta "Server version"
 .It Li "window_active" Ta "" Ta "1 if window active"
 .It Li "window_active_clients" Ta "" Ta "Number of clients viewing this window"
 .It Li "window_active_clients_list" Ta "" Ta "List of clients viewing this window"

tmux.c

@@ -18,6 +18,7 @@
 
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/utsname.h>
 
 #include <err.h>
 #include <errno.h>
@@ -212,6 +213,20 @@ find_home(void)
 	return (home);
 }
 
+const char *
+getversion(void)
+{
+	static char	*version;
+	struct utsname	 u;
+
+	if (version == NULL) {
+		if (uname(&u) < 0)
+			fatalx("uname failed");
+		xasprintf(&version, "openbsd-%s", u.release);
+	}
+	return version;
+}
+
 int
 main(int argc, char **argv)
 {
@@ -238,7 +253,7 @@ main(int argc, char **argv)
 		flags = 0;
 
 	label = path = NULL;
-	while ((opt = getopt(argc, argv, "2c:Cdf:lL:qS:uUv")) != -1) {
+	while ((opt = getopt(argc, argv, "2c:Cdf:lL:qS:uUvV")) != -1) {
 		switch (opt) {
 		case '2':
 			flags |= CLIENT_256COLOURS;
@@ -255,6 +270,9 @@ main(int argc, char **argv)
 		case 'f':
 			set_cfg_file(optarg);
 			break;
+ 		case 'V':
+			printf("%s %s\n", getprogname(), getversion());
+ 			exit(0);
 		case 'l':
 			flags |= CLIENT_LOGIN;
 			break;

tmux.h

@@ -1769,6 +1769,7 @@ int		 areshell(const char *);
 void		 setblocking(int, int);
 const char	*find_cwd(void);
 const char	*find_home(void);
+const char	*getversion(void);
 
 /* proc.c */
 struct imsg;