On 4/30/17 2:31 PM, Florian Mayer wrote:
> I want to add up all numbers from 1 to 10, but when I do
> $ echo $(({1,10}’+’ +0)) # with a space between the first + and the second one
> I get an error:
> bash: ((: 1+ ,3 10+ ,3: syntax error: operand expected (error token is ",3
> 10+ ,3“)
First of all, this is too clever by half. There are many clearer ways to
add the numbers from 1 to 10. Second, you are using a comma where you
probably mean `..'.
Once you take out the weird UTF-8 quotes, brace expansion isn't performed
at all. It never has been performed on something that looks like it could
be a command substitution (it defers to the subshell that's started to run
the command substitution). A future version of bash will probably assume
that $(( begins an arithmetic substitution and perform the expansion, but
no version of bash does that today.
Even if you were using a modified version of bash that did this, there is
no way you would get `,3' out of it, since it doesn't appear anywhere in
the original statement.
>
> It seems as if brace expansion gets executed first (as expected) but with
> all the spaces removed that had existed before inside the (( )) parentheses
> pair.
> The line
> $ (( {1, 10}'+' ,3)) # (space between 1 and 10)
> also gives the same error and thus shows that spaces are removed before
> brace expansion takes place. Why is that?
This does perform brace expansion, but it expands to two words
" 1+ ,3" and " 10+ ,3"
which eventually get passed to the expression evaluator as
" 1+ ,3 10+ ,3"
It's very hard to figure out what you might be expecting here.
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU [email protected] http://cnswww.cns.cwru.edu/~chet/
