Greenbaum was a co-writer with Jim Fritzell of Mister Peepers an important early television show created by David Swift and starring Wally Cox.
[2][3] In the mid 1950s, Greenbaum teamed with Jim Fritzell and collaborated on scripts for the TV series Mister Peepers (1952), a stylish sitcom starring Wally Cox as a timid small-town science teacher; it also gave Tony Randall his first important role.
These included the Walter Brennan sitcom The Real McCoys (1957–62), The Andy Griffith Show (1960–68) and M*A*S*H, on which they worked for five years, contributing 35 episodes.
On his own, Greenbaum wrote two books, including the memoir The Goldenberg Who Couldn't Dance, and 'The Tenth Life of Osiris Oaks' (with Wally Cox), and worked on The George Gobel Show.
[7] In a book published the year of Greenbaum's death, Don Knotts recalled of him, "Everett would come up with lines right out of the blue that would knock you off your seat.