What did Doug McIlroy contribute to Unix and Bell Labs, according to Brian Kernighan?

Brian Kernighan described Doug McIlroy as exceptionally good at almost anything he chose to do. McIlroy wrote the Unix sort and diff programs, did his own language design, wrote one of the first PL/I compilers and invented the idea of macros. Kernighan rated his biggest role as constructive technical critic: as the department head over Ken Thompson he never told Thompson what to do, but his criticism made the work better throughout his Bell Labs career.

• McIlroy was Kernighan's boss on his first internship, around 1967, and let him drift to an unrelated project.
• McIlroy was the outside reader on Kernighan's PhD thesis and improved both its writing and content.
• Kernighan said McIlroy stayed at Bell Labs until retiring in roughly the early to mid 1990s.

Source: our own transcription of the episode. The full conversation is on Ryan Peterman (2026-11-05). Read the whole episode summary →

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