From: tamouse mailing lists <tamouse.lists@...>
Date: 2013-04-24T13:00:52+09:00
Subject: Re: what is the $- magic global?

On Tue, Apr 23, 2013 at 9:21 PM, Matthew Kerwin <lists@ruby-forum.com> wrote:
> Also: I'm aware of bash's $- options description, but that doesn't seem
> relevant in this case; bash's $- is a simple string, and doesn't have
> any magic attached.
>
> I know that perl and ruby both have a similarly-defined $+ magic
> variable.  Perl also has a $- ("The number of lines left on the page of
> the currently selected output channel.") but I doubt there's a
> correlation with ruby's, because perl's is a simple integer, and is
> related to $~ and $= which are completely different between the two
> languages.
>
> I've also encountered perl's @-/@+ match offsets, but can't see how
> they'd be relevant.

Hummm... I'm flummoxed as well. I just went through the newest
Programming Ruby book (beta 2) and cannot find anything referencing
$-. It lists these:

$-0 → String Synonym for $/
$-F → String Synonym for $;
$-a → Object True if the -a option is specified on the command line
$-d → Object Synonym for $DEBUG.
$-i → String If in-place edit mode is enabled (perhaps using the -i
command-line option), $-i holds the extension used when creating the
backup file.
$-I → Array Synonym for $:
$-l → Object Set to true if the -l option (which enables line-end
processing) is present on the command line.
$-p → Object Set to true if the -p option (which puts an implicit
while gets...end loop around your program) is present on the command
line.
$-v → Object Synonym for $VERBOSE.
$-w → Object Synonym for $VERBOSE.
$-W → Object Return the value set by the -W command-line option.

and this:

"a global variable name can be formed using $- followed by a single
letter or underscore" [p 318 in PDF]

but no bare $- variable....