Save logging filename in pane-specific variable

When logging is started, save the name of the log file in the variable.
When logging is stopped, use the variable to display the name of the
file, then clear the variable.  Use whether the variable is empty or not
to determine if logging has been started.

scripts/toggle_logging.sh

@@ -10,19 +10,21 @@ start_pipe_pane() {
 	local file=$(expand_tmux_format_path "${logging_full_filename}")
 	"$CURRENT_DIR/start_logging.sh" "${file}"
 	display_message "Started logging to ${file}"
+	set_logging_variable "${file}"
 }
 
 stop_pipe_pane() {
 	tmux pipe-pane
-	display_message "Ended logging to $logging_full_filename"
+	display_message "Ended logging to $(get_logging_variable)"
+	set_logging_variable ""
 }
 
 # returns a string unique to current pane
 pane_unique_id() {
 	tmux display-message -p "#{session_name}_#{window_index}_#{pane_index}"
 }
 
-# saving 'logging' 'not logging' status in a variable unique to pane
+# saving value in a variable unique to pane
 set_logging_variable() {
 	local value="$1"
 	local pane_unique_id="$(pane_unique_id)"
@@ -31,13 +33,13 @@ set_logging_variable() {
 
 get_logging_variable() {
 	local pane_unique_id="$(pane_unique_id)"
-	local current_pane_logging="$(get_tmux_option "@${pane_unique_id}" "not logging")"
+	local current_pane_logging="$(get_tmux_option "@${pane_unique_id}")"
 	echo $current_pane_logging
 }
 
 # this function checks if logging is happening for the current pane
 is_logging() {
-	if [ "$(get_logging_variable)" == "logging" ]; then
+	if [ -n "$(get_logging_variable)" ]; then
 		return 0
 	else
 		return 1
@@ -47,10 +49,8 @@ is_logging() {
 # starts/stop logging
 toggle_pipe_pane() {
 	if is_logging; then
-		set_logging_variable "not logging"
 		stop_pipe_pane
 	else
-		set_logging_variable "logging"
 		start_pipe_pane
 	fi
 }