Add pane_start_path to match start_command.

format.c

@@ -801,6 +801,20 @@ format_cb_start_command(struct format_tree *ft)
 	return (cmd_stringify_argv(wp->argc, wp->argv));
 }
 
+/* Callback for pane_start_path. */
+static void *
+format_cb_start_path(struct format_tree *ft)
+{
+	struct window_pane	*wp = ft->wp;
+
+	if (wp == NULL)
+		return (NULL);
+
+	if (wp->cwd == NULL)
+		return (xstrdup(""));
+	return (xstrdup(wp->cwd));
+}
+
 /* Callback for pane_current_command. */
 static void *
 format_cb_current_command(struct format_tree *ft)
@@ -2898,6 +2912,9 @@ static const struct format_table_entry format_table[] = {
 	{ "pane_start_command", FORMAT_TABLE_STRING,
 	  format_cb_start_command
 	},
+	{ "pane_start_path", FORMAT_TABLE_STRING,
+	  format_cb_start_path
+	},
 	{ "pane_synchronized", FORMAT_TABLE_STRING,
 	  format_cb_pane_synchronized
 	},

tmux.1

@@ -5195,6 +5195,7 @@ The following variables are available, where appropriate:
 .It Li "pane_right" Ta "" Ta "Right of pane"
 .It Li "pane_search_string" Ta "" Ta "Last search string in copy mode"
 .It Li "pane_start_command" Ta "" Ta "Command pane started with"
+.It Li "pane_start_path" Ta "" Ta "Path pane started with"
 .It Li "pane_synchronized" Ta "" Ta "1 if pane is synchronized"
 .It Li "pane_tabs" Ta "" Ta "Pane tab positions"
 .It Li "pane_title" Ta "#T" Ta "Title of pane (can be set by application)"