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.
