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I was wondering if there's a known reason behind the use of .. to represent the parent of the current directory in most operating systems.

The reason I ask this question is because I think that the colon character (:) could have been a better idea instead. For one, it uses one character less. Also, it can visually represent the concept of "the directory above this directory", since a colon is a dot above a dot, and a dot represents a directory.

But whether you agree with me or not, I'm just curious about the history of .. in operating systems. That's all.

jasonwryan
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Francis Ocoma
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  • Conjecture: the convention that files with names beginning with . are hidden by default predates the special meanings of . and ..; and part of the reason that . and .. were selected is so that these special entries that appear in every directory would be hidden by default. – Celada Nov 18 '14 at 06:32
  • on a side note, given a unix /foo/bar/baz directory. on Multics, in the old days, assumming you are in bar directory. You would refer file in baz using bar>baz>myfile and file in foo using <myfile, with < and > meaning up and down. As those have a different meaning in linux, they could not be used for files and dirs. – Archemar Nov 18 '14 at 08:41
  • @Celada It might be the other way around. I suspect that . and .. came first, and they were hidden by default, then they developed the convention of using other files beginning with . as config files, and also hiding those. – Barmar Nov 18 '14 at 16:42
  • I tried googling "history of unix file system", but none of the papers seem to address this naming convention. Not even Ritchie's conference paper: http://cm.bell-labs.com/who/dmr/hist.html – Barmar Nov 18 '14 at 16:45
  • I suspect they chose .. rather than : because it's easier to type, it doesn't require a shift key. I wonder if it's a coincidence that . and / are adjacent on the keyboard. – Barmar Nov 18 '14 at 16:48
  • The colon is used as a path separator on unix and linux systems. – stoeff Nov 18 '14 at 18:45
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    @Barmar I'd suspect that is indeed the case. I remember reading that the convention of having .files hidden was born by a bug in ls, where any entry beginning with . got hidden. .. Ah yes: http://unix.stackexchange.com/questions/88875/why-are-filenames-that-start-with-a-dot-hidden-can-i-hide-files-without-using-a – muru Nov 19 '14 at 22:12

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