Re*: [PATCH] t1503: Fix arithmetic expansion syntax error when using dash
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Sep 22, 2010, 19:15 UTC
- Message-ID
- <7viq1xsi7a.fsf@alter.siamese.dyndns.org>
- In-Reply-To
- <4C98EF25.4070700@ramsay1.demon.co.uk>
Ramsay Jones <ramsay@ramsay1.demon.co.uk> writes:
Show 9 quoted lines
> 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 '$N' rather than simply 'N'.
>
> Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>Thanks.
POSIX wants shells to support both "N" and "$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 ))'
23I 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@pobox.com> --- 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.