Interesting! I wonder if any shells that support $((..)) do not support ((..) though. The update 2017 standard mentions ((..)) but not in the obvious place.

Interesting! I wonder if any shells that support $((..)) do not support ((..) though. The update 2017 standard mentions ((..)) but not in the obvious place. It's under 'compound commands/grouping' ... https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_09_04 https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V... > If a character sequence beginning with "((" would be parsed by the shell as an arithmetic expansion if preceded by a '$', shells which implement an extension whereby "((expression))" is evaluated as an arithmetic expression may treat the "((" as introducing as an arithmetic evaluation instead of a grouping command. A conforming application shall ensure that it separates the two leading '(' characters with white space to prevent the shell from performing an arithmetic evaluation.