overflow behavior differs from other shells

[Elliott Hughes]

$ mksh -c 'echo $((0x7fffffff + 1))'
-2147483648

versus:

$ dash -c 'echo $((0x7fffffff + 1))'
2147483648
$ bash -c 'echo $((0x7fffffff + 1))'
2147483648
$ busybox sh -c 'echo $((0x7fffffff + 1))'
2147483648
$ zsh -c 'echo $((0x7fffffff + 1))'
2147483648

[Elliott Hughes (enh-9)]

(this seen with R55 but also at least as far back as R46, so not a recent regression.)

[Thorsten Glaser (mirabilos)]

Not a bug, everything works as intended and documented.

More helpful answer:

If you want POSIX semantics for overflow (have the shell use the host C “long” data type for arithmetics), use the “lksh” binary (l as in long, legacy), see the lksh(1) manpage.

However *do* be aware that 'echo $((0x7FFFFFFF + 1))' on a system with 32-bit long, with POSIX semantics (lksh, GNU bash, dash, …) is ALLOWED TO REMOVE ALL DATA (equal 'rm -rf ~ /') or otherwise crash the system due to ISO C99 Undefined Behaviour. DO NOT DO THAT!