[TUHS] A question about ls(1)

Dan Cross crossd at gmail.com
Sun Apr 28 21:47:35 AEST 2019

On Sat, Apr 27, 2019 at 10:26 AM Anthony Martin <ality at pbrane.org> wrote:

> From at least V2 to V6, the ls(1) command would not
> show directory entries whose names began with a '.'
> unless the -a flag was supplied.
> This was changed in V7: only the directory entries
> for "." and ".." would be skipped by default.
> All further versions of Research Unix retain the
> convention of V7 and Plan 9 ultimately made it
> unnecessary. However, BSD and its descendants did
> not follow suit. Instead, they continued behaving
> like V6 with an additional -A flag to emulate V7.
> Was the initial behavior intentional or just a
> matter of expediency?

I believe it's been publicly stated that it was a mistake in early Unix.
Apparently, Rob Pike had a Google+ post to this effect back in 2012 (or
earlier): I see a reference to it from another mailing list around that
time. Unfortunately, the Google+ content is now lost. Rob, do you have a

Who made the change and what was their motivation?
> Was it a reaction to the intentional hiding of what
> came to be known as "dot files"?

Speaking from memory, I think the intent was to avoid showing '.' and '..',
and that a programming error accidentally hid all dotfiles; probably this
went unnoticed because there just weren't many of them at the time. This
was corrected in 7th Edition, but the existing behavior had already escaped
into the world via Berkeley.

I suspect the "dot file" convention came later, as a side-effect of
observed behavior of ls.

        - Dan C.
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