On 2019-10-04 09:15:41 +1000, Chris Angelico wrote: > On Fri, Oct 4, 2019 at 9:08 AM Cameron Simpson <c...@cskk.id.au> wrote: > > On 03Oct2019 23:55, Chris Angelico <ros...@gmail.com> wrote: > > >In the shell, the first two are an empty string, then ':' is a > > >colon, which introduces a label (the fact that it's in quotes is > > >irrelevant to the shell). So there's an empty label followed by a > > >shell comment. > > > > No. ":" is a synonym for "true". (Like "[" is a synonym for "test".) > > > > There aren't labels in the shell. This is just a dummy "true" command, > > with a comment. > > My bad. I remember using a leading colon-space as a multi-shell > comment, and in at least some of them, it's a label
You may actually be onto something here. I came across this interesting[1] paper: http://doc.cat-v.org/unix/unix-reader/A.Research.UNIX.Reader.complete.pdf which mentions: GOTO, : (v2 pages 37-38) Goto manipulated the standard input to give the illusion of a programmable shell (Thompson, v2) The associated : command, which thanks to ASCII collating sequence boasted the first page in the manual, was a big nop. It doesn't explicitely say what : was used for, but since it was associated with goto, it was very likely used to mark a label. The Bourne shell, introduced with v7, doesn't have goto, but retained : as a no-op. hp [1] To Unix history afficionados. -- _ | Peter J. Holzer | we build much bigger, better disasters now |_|_) | | because we have much more sophisticated | | | h...@hjp.at | management tools. __/ | http://www.hjp.at/ | -- Ross Anderson <https://www.edge.org/>
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