A Boy and His Dog is a 1975 American black comedy science fiction film directed by actor L. Q. Jones, from a screenplay by Jones based on the 1969 novella of the same title by fantasy author Harlan Ellison. The film stars Don Johnson, Susanne Benton, Alvy Moore, and Jason Robards.
https://en.m.wikipedia.org/wiki/A_Boy_and_His_Dog_(1975_film)
Great movie. It is also on youtube, as of a few days ago.