Re: Docs typo, :- vs -

[Greg Wooledge]

On Fri, Jan 31, 2025 at 01:42:38 +0100, Alfred Agrell wrote:
> Hello
> 
> https://git.savannah.gnu.org/cgit/bash.git/tree/doc/bash.info#n1842
> 
> '${PARAMETER:-WORD}'
>      If PARAMETER is unset or null, the expansion of WORD is
>      substituted.  Otherwise, the value of PARAMETER is substituted.
> 
>           $ v=123
>           $ echo ${v-unset}
>           123
> 
> The heading says :-, but the example just says -. Which one is intended? Or
> is it supposed to say that both are equivalent?

They both exist, and mean slightly different things.

Right above the list of examples, there's this paragraph:

       When not performing substring expansion, using the forms documented be‐
       low  (e.g.,  :-),  bash  tests  for  a parameter that is unset or null.
       Omitting the colon results in a test only for a parameter that  is  un‐
       set.

Everyone overlooks this.  Even POSIX finally caved in and added examples
showing both syntaxes, not expecting the reader to extrapolate from
multiple sources.