Originally Posted by Scrutinizer

I haven't come across a situation where leaving out the $-sign did not work. Also, I found this:
Arithmetic Expansion

[...]

> using integer variables even without the $ symbol you don't care
I use $ in arithmetic expressions because there are shells
that fail if it is not there.

> [*] BTW, are there shells that support $((...)) but require to
> prefix 'i' by '$'?

Old versions of dash. The version in Debian etch requires the $, but
the current version doesn't.
Since dash is based on ash, maybe ash is the same.

> Since dash is based on ash, maybe ash is the same.

ash didn't have support for $((...)) as it predates it. It did
have and expr builtin though. debian ash is based on NetBSD sh,
that one being based on ash as in all the other BSDs where sh is
not based on pdksh.

I don't know whether the change that allows variables without $
has made it to NetBSD sh, but a quick read of
http://cvsweb.netbsd.org/bsdweb.cgi/...rev=1.18&conte...
would seem to indicate it didn't.

Note that $((i * 2)) is not the same as $(($i * 2)) if $i is for
instance "1 + 1" in most shell implementations (the wording is
not clear (to me at least) in POSIX but I beleive the result is
unspecified then anyway for $((i * 2)); it's not clear whether
the output of i=-1; echo $((i * 2)) is specified either though I
wouldn't expect any shell to output anything other than -2 if
they do output anything).