Just appending -l to $SHELL to create a login shell is wrong: -l is not POSIX,

and some people may use shells which do not support it. Instead, make an empty
default-command option mean a login shell, and fork it with a - in argv[0]
which is the method used by login(1).

Also fix the automatic-rename code to handle this correctly and to strip a
leading - if present.

names.c

@@ -59,7 +59,16 @@ set_window_names(void)
 		if (name == NULL)
 			wname = default_window_name(w);
 		else {
-			wname = parse_window_name(name);
+			/* 
+			 * If tmux is using the default command, it will be a
+			 * login shell and argv[0] may have a - prefix. Remove
+			 * this if it is present. Ick.
+			 */
+			if (w->active->cmd != NULL && *w->active->cmd == '\0' &&
+			    name != NULL && name[0] == '-' && name[1] != '\0')
+				wname = parse_window_name(name + 1);
+			else
+				wname = parse_window_name(name);
 			xfree(name);
 		}
 
@@ -78,7 +87,9 @@ default_window_name(struct window *w)
 {
 	if (w->active->screen != &w->active->base)
 		return (xstrdup("[tmux]"));
-	return (parse_window_name(w->active->cmd));
+	if (w->active->cmd != NULL && *w->active->cmd != '\0')
+		return (parse_window_name(w->active->cmd));
+	return (parse_window_name(window_default_command()));
 }
 
 char *

tmux.1

@@ -1070,8 +1070,12 @@ maintain this maximum length.
 Set the command used for new windows (if not specified when the window is
 created) to
 .Ar command .
-The default is
+The default is an empty string, which instructs
-.Dq exec $SHELL -l .
+.Nm
+to create a login shell using the
+.Ev SHELL
+environment variable or, if it is unset, the user's shell returned by
+.Xr getpwuid 3 .
 .It Ic default-path Ar path
 Set the default working directory for processes created from keys, or
 interactively from the prompt.

tmux.c

@@ -209,7 +209,6 @@ main(int argc, char **argv)
  	struct cmd		*cmd;
 	struct pollfd	 	 pfd;
 	struct hdr	 	 hdr;
-	const char		*shell;
 	struct passwd		*pw;
 	char			*s, *path, *label, *cause, *home, *pass = NULL;
 	char			 cwd[MAXPATHLEN];
@@ -270,6 +269,7 @@ main(int argc, char **argv)
 	options_init(&global_s_options, NULL);
 	options_set_number(&global_s_options, "bell-action", BELL_ANY);
 	options_set_number(&global_s_options, "buffer-limit", 9);
+	options_set_string(&global_s_options, "default-command", "%s", "");
 	options_set_number(&global_s_options, "display-time", 750);
 	options_set_number(&global_s_options, "history-limit", 2000);
 	options_set_number(&global_s_options, "lock-after-time", 0);
@@ -358,17 +358,6 @@ main(int argc, char **argv)
 	}
 	xfree(label);
 
-	shell = getenv("SHELL");
-	if (shell == NULL || *shell == '\0') {
-		pw = getpwuid(getuid());
-		if (pw != NULL)
-			shell = pw->pw_shell;
-		if (shell == NULL || *shell == '\0')
-			shell = _PATH_BSHELL;
-	}
-	options_set_string(
-	    &global_s_options, "default-command", "exec %s -l", shell);
-
 	if (getcwd(cwd, sizeof cwd) == NULL) {
 		pw = getpwuid(getuid());
 		if (pw->pw_dir != NULL && *pw->pw_dir != '\0')

tmux.h

@@ -1408,6 +1408,7 @@ int	 screen_check_selection(struct screen *, u_int, u_int);
 
 /* window.c */
 extern struct windows windows;
+const char	*window_default_command(void);
 int		 window_cmp(struct window *, struct window *);
 int		 winlink_cmp(struct winlink *, struct winlink *);
 RB_PROTOTYPE(windows, window, entry, window_cmp);

window.c

@@ -23,6 +23,7 @@
 #include <fcntl.h>
 #include <fnmatch.h>
 #include <paths.h>
+#include <pwd.h>
 #include <signal.h>
 #include <stdint.h>
 #include <stdlib.h>
@@ -57,6 +58,23 @@ struct windows windows;
 
 RB_GENERATE(winlinks, winlink, entry, winlink_cmp);
 
+const char *
+window_default_command(void)
+{
+	const char	*shell;
+	struct passwd	*pw;
+
+	shell = getenv("SHELL");
+	if (shell != NULL && *shell != '\0')
+		return (shell);
+
+	pw = getpwuid(getuid());
+	if (pw != NULL && pw->pw_shell != NULL && *pw->pw_shell != '\0')
+		return (pw->pw_shell);
+
+	return (_PATH_BSHELL);
+}
+
 int
 winlink_cmp(struct winlink *wl1, struct winlink *wl2)
 {
@@ -424,7 +442,8 @@ window_pane_spawn(struct window_pane *wp,
 {
 	struct winsize	 ws;
 	int		 mode;
-	const char     **envq;
+	const char     **envq, *ptr;
+	char		*argv0;
 	struct timeval	 tv;
 
 	if (wp->fd != -1)
@@ -465,7 +484,18 @@ window_pane_spawn(struct window_pane *wp,
 		sigreset();
 		log_close();
 
-		execl(_PATH_BSHELL, "sh", "-c", wp->cmd, (char *) NULL);
+		if (*wp->cmd != '\0') {
+			execl(_PATH_BSHELL, "sh", "-c", wp->cmd, (char *) NULL);
+			fatal("execl failed");
+		}
+
+		/* No command; fork a login shell. */
+		cmd = window_default_command();
+		if ((ptr = strrchr(cmd, '/')) != NULL && *(ptr + 1) != '\0')
+			xasprintf(&argv0, "-%s", ptr + 1);
+		else
+			xasprintf(&argv0, "-%s", cmd);
+		execl(cmd, argv0, (char *) NULL);
 		fatal("execl failed");
 	}