Auto-update $DISPLAY within tmux

Help avoid stale values for $DISPLAY which breaks X11 forwarding.

.bash_profile

@@ -18,6 +18,18 @@ source ~/.bash/z/z.sh
 
 # Load the shell dotfiles
 for file in ~/.{exports,aliases,functions,bash_prompt,bash.local}; do
-  [ -r "$file" ] && source "$file"
+	[ -r "$file" ] && source "$file"
 done
 unset file
+
+# Ran before every command
+preexec() {
+	# Don't cause a preexec for PROMPT_COMMAND
+	# Beware! This fails if PROMPT_COMMAND is a string with more than one command
+	[ "$BASH_COMMAND" = "$PROMPT_COMMAND" ] && return
+
+	# Update $DISPLAY to help avoid stale values within tmux
+	update-x11-forwarding
+}
+
+trap 'preexec' DEBUG

.functions

@@ -195,3 +195,17 @@ haste() {
 	echo "Upload failed."
 	return 1
 }
+
+# Cache $DISPLAY if we're not in tmux, otherwise update from the cache
+# Based on: http://alexteichman.com/octo/blog/2014/01/01/x11-forwarding-and-terminal-multiplexers/
+update-x11-forwarding() {
+	if [ ! -f ~/.display ]; then
+		touch ~/.display
+	fi
+
+	if [ -z "$TMUX" ]; then
+		echo $DISPLAY > ~/.display
+	else
+		export DISPLAY=`cat ~/.display`
+	fi
+}