[TUHS] Were cron and at done at the same time? Or one before the other?
M Douglas McIlroy
m.douglas.mcilroy at dartmouth.edu
Wed Dec 9 14:35:24 AEST 2020
This pair of commands exemplifies a weakness in the way Unix evolved.
Although it was the product of a shared vision, It was not a
product-oriented project. Unix commands work well together, but they
don't necessarily work alike.
It would be nice if identifiable families of commands had similar user
interfaces. However, cron and at were written by different
individuals, apparently with somewhat different tastes. Unix folks
were close colleagues, but had no organized design committee.
Time specs in cron and at are markedly different. A more consequential
example is data-field specs (or lack thereof) in sort, join, cut, comm
and uniq. The various specs were recognized as "wildly incongruent" in
a BUG remak. However there was no impetus for unification. To
paraphrase John Cocke (speaking about Fortran): one must understand
that Unix commands are not a logical language. They are a natural
language--in the sense that they developed by organic evolution, not
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