Add -E to detach-client to exec a command to replace the client instead

of exiting it, useful if tmux wasn't exec'd itself. From Jenna Magius.

client.c

@@ -51,6 +51,8 @@ static enum {
 static int		 client_exitval;
 static enum msgtype	 client_exittype;
 static const char	*client_exitsession;
+static const char	*client_execshell;
+static const char	*client_execcmd;
 static int		 client_attached;
 
 static __dead void	 client_exec(const char *,const char *);
@@ -358,6 +360,14 @@ client_main(struct event_base *base, int argc, char **argv, int flags,
 	/* Start main loop. */
 	proc_loop(client_proc, NULL);
 
+	/* Run command if user requested exec, instead of exiting. */
+	if (client_exittype == MSG_EXEC) {
+		if (client_flags & CLIENT_CONTROLCONTROL)
+			tcsetattr(STDOUT_FILENO, TCSAFLUSH, &saved_tio);
+		clear_signals(0);
+		client_exec(client_execshell, client_execcmd);
+	}
+
 	/* Print the exit message, if any, and exit. */
 	if (client_attached) {
 		if (client_exitreason != CLIENT_EXIT_NONE)
@@ -655,6 +665,16 @@ client_dispatch_attached(struct imsg *imsg)
 			client_exitreason = CLIENT_EXIT_DETACHED;
 		proc_send(client_peer, MSG_EXITING, -1, NULL, 0);
 		break;
+	case MSG_EXEC:
+		if (datalen == 0 || data[datalen - 1] != '\0' ||
+		    strlen(data) + 1 == (size_t)datalen)
+			fatalx("bad MSG_EXEC string");
+		client_execcmd = xstrdup(data);
+		client_execshell = xstrdup(data + strlen(data) + 1);
+
+		client_exittype = imsg->hdr.type;
+		proc_send(client_peer, MSG_EXITING, -1, NULL, 0);
+		break;
 	case MSG_EXIT:
 		if (datalen != 0 && datalen != sizeof (int))
 			fatalx("bad MSG_EXIT size");

cmd-detach-client.c

@@ -33,8 +33,9 @@ const struct cmd_entry cmd_detach_client_entry = {
 	.name = "detach-client",
 	.alias = "detach",
 
-	.args = { "as:t:P", 0, 0 },
-	.usage = "[-P] [-a] [-s target-session] " CMD_TARGET_CLIENT_USAGE,
+	.args = { "aE:s:t:P", 0, 0 },
+	.usage = "[-aP] [-E shell-command] "
+	         "[-s target-session] " CMD_TARGET_CLIENT_USAGE,
 
 	.sflag = CMD_SESSION,
 	.tflag = CMD_CLIENT,
@@ -63,6 +64,7 @@ cmd_detach_client_exec(struct cmd *self, struct cmdq_item *item)
 	struct client	*c = item->state.c, *cloop;
 	struct session	*s;
 	enum msgtype	 msgtype;
+	const char	*cmd = args_get(args, 'E');
 
 	if (self->entry == &cmd_suspend_client_entry) {
 		tty_stop_tty(&c->tty);
@@ -79,20 +81,31 @@ cmd_detach_client_exec(struct cmd *self, struct cmdq_item *item)
 	if (args_has(args, 's')) {
 		s = item->state.sflag.s;
 		TAILQ_FOREACH(cloop, &clients, entry) {
-			if (cloop->session == s)
-				server_client_detach(cloop, msgtype);
+			if (cloop->session == s) {
+				if (cmd != NULL)
+					server_client_exec(cloop, cmd);
+				else
+					server_client_detach(cloop, msgtype);
+			}
 		}
 		return (CMD_RETURN_STOP);
 	}
 
 	if (args_has(args, 'a')) {
 		TAILQ_FOREACH(cloop, &clients, entry) {
-			if (cloop->session != NULL && cloop != c)
-				server_client_detach(cloop, msgtype);
+			if (cloop->session != NULL && cloop != c) {
+				if (cmd != NULL)
+					server_client_exec(cloop, cmd);
+				else
+					server_client_detach(cloop, msgtype);
+			}
 		}
 		return (CMD_RETURN_NORMAL);
 	}
 
-	server_client_detach(c, msgtype);
+	if (cmd != NULL)
+		server_client_exec(c, cmd);
+	else
+		server_client_detach(c, msgtype);
 	return (CMD_RETURN_STOP);
 }

server-client.c

@@ -296,6 +296,32 @@ server_client_detach(struct client *c, enum msgtype msgtype)
 	proc_send_s(c->peer, msgtype, s->name);
 }
 
+/* Execute command to replace a client, */
+void
+server_client_exec(struct client *c, const char *cmd)
+{
+	struct session	*s = c->session;
+	char		*msg, *shell;
+	size_t		 cmdsize, shellsize;
+
+	if (*cmd == '\0')
+		return;
+	cmdsize = strlen(cmd) + 1;
+
+	if (s != NULL)
+		shell = options_get_string(s->options, "default-shell");
+	else
+		shell = options_get_string(global_s_options, "default-shell");
+	shellsize = strlen(shell) + 1;
+
+	msg = xmalloc(cmdsize + shellsize);
+	memcpy(msg, cmd, cmdsize);
+	memcpy(msg + cmdsize, shell, shellsize);
+
+	proc_send(c->peer, MSG_EXEC, -1, msg, cmdsize + shellsize);
+	free(msg);
+}
+
 /* Check for mouse keys. */
 static key_code
 server_client_check_mouse(struct client *c)

tmux.1

@@ -724,6 +724,7 @@ is used, the
 option will not be applied.
 .It Xo Ic detach-client
 .Op Fl aP
+.Op Fl E Ar shell-command
 .Op Fl s Ar target-session
 .Op Fl t Ar target-client
 .Xc
@@ -740,6 +741,11 @@ If
 .Fl P
 is given, send SIGHUP to the parent process of the client, typically causing it
 to exit.
+With
+.Fl E ,
+run
+.Ar shell-command
+to replace the client.
 .It Ic has-session Op Fl t Ar target-session
 .D1 (alias: Ic has )
 Report an error and exit with 1 if the specified session does not exist.

tmux.h

@@ -443,6 +443,7 @@ enum msgtype {
 	MSG_SUSPEND,
 	MSG_UNLOCK,
 	MSG_WAKEUP,
+	MSG_EXEC,
 };
 
 /*
@@ -1880,6 +1881,7 @@ int	 server_client_open(struct client *, char **);
 void	 server_client_unref(struct client *);
 void	 server_client_lost(struct client *);
 void	 server_client_detach(struct client *, enum msgtype);
+void	 server_client_exec(struct client *, const char *);
 void	 server_client_loop(void);
 void	 server_client_push_stdout(struct client *);
 void	 server_client_push_stderr(struct client *);