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lang-bash
$( ... )is command substitution,$(( ... ))is arithmetic expansion. (If you're running that on an interactive Bash, the error message should begin withbash: ..., implying it's from Bash and not sed.) I can't tell any reason why the parentheses would have been doubled there. The other issue is with double quotes""vs. single quotes'', see What is the difference between the "...", '...', $'...', and $"..." quotes in the shell?