What is the song Dennis Hopper sings in Cool Hand luke movie?

The song Dennis Hopper sings in "Cool Hand Luke" is "The Good, The Bad and The Ugly" by Ennio Morricone. It's the main theme song from the 1966 spaghetti western film of the same name, which is playing on the jukebox in the prison dining hall. Hopper sings a few lines of the song while Luke is trying to eat his 50 eggs.

The song is iconic and well-known, and it perfectly captures the mood of the scene in the movie.