$(( expression )) error?

[wisecracker-bazza]

Take the code below.
[code]

!/bin/sh

txt="1234567890"
echo "$(( $txt ))"
echo "$(( ${#txt} - 1 ))"
echo "$(( #txt - 1 ))"
[/code]
Shell Check ERROR window.

[code]
$ shellcheck myscript

Line 3:
echo "$(( $txt ))"
^-- SC2004: $/${} is unnecessary on arithmetic variables.

$
[/code]
Your code says '$/${} are unnecessary with no other errors.
Now try running line 5 on sh, bash, ksh and zsh.
This is at least one exception to the rule.
TIA.
Bazza.

[koalaman]

You're right, but shellcheck also does not produce a warning for echo "$(( ${#txt} - 1 ))".

It only produces a warning where the $ is unnecessary, on line 3.

I've updated the wiki to mention this explicitly.