Junio C Hamano <gitster@xxxxxxxxx> writes:
> One thing I was wondering about the $(( ... )) syntax while reading
> this thread was about the SP around the expression, i.e.
>
> var=$(( $term1 * $term2 + $term3 ))
>
> vs
>
> var=$(($term1 * $term2 + $term3))
>
> I personally do not have strong preference between the two, but I
> have a vague impression that we preferred the former because
> somebody in the past gave us a good explanation why we should.
>
> "git grep" however seems to tell us that we are not clearly decided
> between the two, so I probably am misremembering it and there is no
> preference either way.
One thing that is somewhat related is that we would want to avoid
writing things like this by mistake:
var=$((cmd1 && cmd2) | cmd3)
which is not meant to be an arithmetic expansion, but is a command
substitution that happens to have a subshell at the head of the
pipeline. I think bash gets this right, but some shells (e.g. dash)
tries to parse this as an arithmetic expansion upon seeing "$((" and
fails to parse it, waiting forever until it sees the matching "))".
So we write it like this to make it safer:
var=$( (cmd1 && cmd2) | cmd3 )
Perhaps having a SP after $(( of a real arithmetic expression, i.e.
var=$(( ... anything ... ))
makes it easier to tell these two apart? I dunno.
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