False positive warning for ls about shellcheck

[koalaman]

Verified and fixed.

[grimreaper]

This should still warn as a non-portable extension. some ls(1) lack the -N option

[arth1]

Because ls is an external command (unless you use tcsh), it is non-portable by nature. Sure, it could be BusyBox ls or a legacy Unix system, but if warning against that, surely one would have to warn about hundreds of commands and non-portable options, including (but not limited to) "ps -m", and "find -print0" | "xargs -0" and even "echo -n". One could, I suppose, check for POSIXLY_CORRECT or "set -p" and limit the well-known commands when that's in effect.

I'm of the opinion that when external programs are called, the caller is responsible for the arguments being supported where the script is run. It seems ... easier.

[grimreaper]

External commands are not non-portable by nature. There is a POSIX standard and provided that this is adhered to one should expect it to work.

echo -n is in POSIX. other echo flags are not. I would expect a warning for, e.g., echo -e to use printf instead.