On 2/18/11 4:32 PM, Peter Hofmann wrote:
> So far, so good. It's what I expected. Let's add another level of
> quotes:
>
> $ echo "$(echo "{1..3}")"
> 1 2 3
>
> Huh? Actually, I was expecting to get the same output as before.
>
> Some debug output:
>
> $ set -x
> $ echo "$(echo "{1..3}")"
> ++ echo 1
> ++ echo 2
> ++ echo 3
> + echo 1 2 3
> 1 2 3
>
> Why's that?
>
> a) As far as I understood, quotes inside of $(...) should not interfere
> with the outer quotes.
> b) Why are there three subshells? Actually, that {1..3} doesn't get
> expanded. It's more like the call above is effectively equivalent to
> this:
>
> $ echo "$(echo 1)" "$(echo 2)" "$(echo 3)"
This is close to the actual expansion.
Brace expansion is strictly textual, is performed before all other
expansions, and doesn't understand a whole lot of shell syntax.
It does understand a little about quoted strings, so what you get is
echo "$(echo "1")" "$(echo "2")" "$(echo "3")"
The preamble is "$(echo ", the portion to be expanded is {1..3}, and the
postscript is ")".
Chet
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU c...@case.edu http://cnswww.cns.cwru.edu/~chet/
