Joined Bell Labs in 1967, Aho co-authored a number of research papers, first with Jeff Ullman, and then with several other co-workers. He soon stumbled upon what would become the UNIX project, and found that using the early system "was a much nicer way to write papers than the old traditional way". Through UNIX, Aho helped develop automata theory and its applications to programming language parsing and compilation.
Aho is the "A" in the command AWK. This language was named by its authors, Al Aho, Peter Weinberger and Brian Kernighan.