Re: /bin/echo -- $var

[Eric Blake]

On 8/14/19 7:01 AM, Harald Dunkel wrote:
> Hi folks,
> 
> I just learned by accident that
> 
>       var="-n"
>       /bin/echo -- $var
> 
> actually prints
> 
>       -- -n

Correct.  This is the POSIX-mandated behavior.

> 
> Shouldn't it be just
> 
>       -n

No, because 'echo' is one of the few exceptions to the rule, in that
POSIX specifically mandates that it NOT recognize -- as an
end-of-options marker.  Instead, POSIX recommends that you use printf
instead of echo if the string you are intending to print may contain \
or start with -.

> ?
> 
> Other tools in coreutils use '--' to indicate "stop parsing for
> command line flags", e.g. touch, ls and rm:
> 
>       % /bin/touch -- -l
>       % /bin/ls -- -l
>       -l
>       % /bin/rm -- -l
>       % /bin/rm -- -l
>       /bin/rm: cannot remove '-l': No such file or directory
> 
> Some common style would be nice here.

It would be nice, but it would be non-compliant to the standards.  We
can't change this one.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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