Doug McIlroy

American computer scientist, mathematician, engineer, and programmer

Malcolm Douglas McIlroy (born 1932) is an American mathematician, engineer, and programmer, best known for having originally developed Unix pipes, software componentry, and several Unix tools, such as spell, diff, sort, join, graph, speak, and tr.

McIlroy (left) with former colleague Dennis Ritchie at the Japan Prize Foundation in May 2011.


  • The notion of "intricate and beautiful complexities" is almost an oxymoron. Unix programmers vie with each other for "simple and beautiful" honors — a point that's implicit in these rules, but is well worth making overt.
  • Word and Excel and PowerPoint and other Microsoft programs have intimate — one might say promiscuous — knowledge of each others' internals. In Unix, one tries to design programs to operate not specifically with each other, but with programs as yet unthought of.
  • Everything was small... and my heart sinks for Linux when I see the size of it. [...] The manual page, which really used to be a manual page, is now a small volume, with a thousand options... We used to sit around in the Unix Room saying, 'What can we throw out? Why is there this option?' It's often because there is some deficiency in the basic design — you didn't really hit the right design point. Instead of adding an option, think about what was forcing you to add that option.
  • Ritchie and Thompson made an amazing team; and they played Unix and C like a fine instrument. They sometimes divided up work almost on a subroutine-by-subroutine basis with such rapport that it almost seemed like the work of a single person. In fact, as Dennis has recounted, they once got their signals crossed and both wrote the same subroutine. The two versions did not merely compute the same result, they did it with identical source code! Their output was prodigious. Once I counted how much production code they had written in the preceding year − 100,000 lines! Prodigious didn’t mean slapdash. Ken and Dennis have unerring design sense. They write code that works, code that can be read, code that can evolve.
  • I don't know the counts of Unix and Linux servers. I do know that my heart sinks whenever I look under the hood in Linux. It is has been so overfed by loving hands. Over 240 system calls! Gigabytes of source! A C compiler with a 250-page user manual (not counting the language definition)! A simple page turner, 'less,' has over 40 options and 60 commands! It's proof that open-source can breed monsters just like the commercial pros. Miraculously, though, this monster works.

Quotes about Doug McIlroy

  • ... speaking of Doug, he's the unsung hero of Unix. He was manager of the group that produced it and a huge creative force in the group, but he's almost unknown in the Unix community. He invented a couple of things you might have heard of: pipes and — get this — macros. Well, someone had to do it and that someone was Doug. As Ken once said when we were talking one day in the Unix room, "There's no one smarter than Doug."
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