Re: ${a:=b} expands to `b', not `a''s value

[Léa Gris]

Le 20/01/2021 à 12:16, Oğuz écrivait :
>      $ declare -l a
>      $ echo "${a:=X} $a"
>      X x
>
> This doesn't jive with what the manual says.
>
> `-l`:
> > When the variable is assigned a value, all upper-case characters are
> converted to lower-case.
>
> `:=`:
> > If parameter is unset or null, the expansion of word is assigned to
> parameter.

The assignation part:
a is assigned X but it is stored as x in a.

> The value of parameter is then substituted.

The expansion part:
The value X is expanded but is not affected by the lowercase 
transformation flag from a, so it remains as X.

The fact that an expansion also assign a value is a questionable design 
choice though.

If I had to use this I would just silence the expansion as an argument 
to the dummy true or : command

: ${a:=X}

> Is this a bug or am I missing something here?

Then likely not.


--
Léa Gris