Re: Exporting functions does not expand aliases in subshells

[Chet Ramey]

On 4/11/24 11:51 AM, Robert Elz wrote:

> For how aliases can mess things up, with the bash way of parsing
> command substitutions, if we do:
>
>         foo() { echo hello; X=$(echo goodbye); echo "$X"; }
>
> and just run foo then we get "hello", "goodbye" (on successive lines).

Let's assume that this is an interactive shell, not in posix mode, since
those make a difference.

> If we then do
>
> alias echo='echo say'
>
> and run foo again (without redefining it) then we get "hello" "say goodbye"
>
> as the first "echo" was already parsed, the (later) alias can't
> affect that one, but the one in the command substitution hasn't
> been (properly) parsed yet, so the alias affects that.

In posix mode, bash does the same thing as ash-based shells.

As has come up several times before, the ad-hoc way bash used to parse
$()-style command substitutions before bash-5.2 -- which was not POSIX-
conformant, but still needs to be supported for backwards compatibility --
drives the difference in behavior.

Chet
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/

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