Ack. Thanks for the info and corrections.
jon.
On 23/09/2010, at 5:15, Junio C Hamano <gitster@xxxxxxxxx> wrote:
> Ramsay Jones <ramsay@xxxxxxxxxxxxxxxxxxx> writes:
>
>> On systems which have dash as /bin/sh, such as Ubuntu, the final
>> test (master@{n} for various n) fails with a syntax error while
>> processing an arithmetic expansion. The syntax error is caused by
>> using a bare name ('N') as a variable reference in the expression.
>>
>> In order to avoid the syntax error, we spell the variable reference
>> as '$N' rather than simply 'N'.
>>
>> Signed-off-by: Ramsay Jones <ramsay@xxxxxxxxxxxxxxxxxxx>
>
> Thanks.
>
> POSIX wants shells to support both "N" and "$N" and requires them to yield
> the same answer to $((N)) and $(($N)), but we should aim for portability
> in a case like this, especially when the price we pay to do so is so
> small, i.e. a few extra dollars.
>
> By the way, on my box, I get this:
>
> $ ls l /bin/dash
> -rwxr-xr-x 1 root root 104024 2008-08-26 02:36 /bin/dash*
> $ dpkg -l dash | grep '^ii'
> ii dash 0.5.4-12 POSIX-compliant shell
> $ /bin/dash -c 'N=20 ; echo $(( N + 3 ))'
> 23
>
> I just left it vague by saying "e.g. older dash" in below, but we may want
> to be more precise in the documentation.
>
> -- >8 --
> CodingGuidelines: spell Arithmetic Expansion with $(($var))
>
> Signed-off-by: Junio C Hamano <gitster@xxxxxxxxx>
> ---
> Documentation/CodingGuidelines | 4 ++++
> 1 files changed, 4 insertions(+), 0 deletions(-)
>
> diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines
> index b8bf618..2cdd76f 100644
> --- a/Documentation/CodingGuidelines
> +++ b/Documentation/CodingGuidelines
> @@ -43,6 +43,10 @@ For shell scripts specifically (not exhaustive):
>
> - We use Arithmetic Expansion $(( ... )).
>
> + - Inside Arithmetic Expansion, spell shell variables with $ in front
> + of them, as some shells do not grok $((x)) while accepting $(($x))
> + just fine (e.g. older dash).
> +
> - No "Substring Expansion" ${parameter:offset:length}.
>
> - No shell arrays.
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