Don't block when executing external commands

src/macro_utilities.cpp

@@ -87,7 +87,7 @@ RunExternalCommand::RunExternalCommand(std::string &&command)
 
 void RunExternalCommand::run()
 {
-	runExternalCommand(m_command, false);
+	runExternalCommand(m_command, true);
 }
 
 RunExternalConsoleCommand::RunExternalConsoleCommand(std::string &&command)
@@ -118,5 +118,6 @@ void runExternalCommand(const std::string &cmd, bool block)
 	if (block)
 		std::system(cmd.c_str());
 	else
-		std::system(("nohup " + cmd + " &").c_str());
+		// If we don't block, disregard any output.
+		std::system(("nohup " + cmd + " >/dev/null 2>&1 &").c_str());
 }

src/status.cpp

@@ -570,7 +570,11 @@ void Status::Changes::songID(int song_id)
 		if (!s.empty())
 		{
 			if (!Config.execute_on_song_change.empty())
-				runExternalCommand(Config.execute_on_song_change, false);
+			{
+				// We need to block to allow sending output to the terminal so a script
+				// can e.g. set the album art.
+				runExternalCommand(Config.execute_on_song_change, true);
+			}
 
 			if (Config.fetch_lyrics_in_background)
 				myLyrics->fetchInBackground(s, false);