From: Julio Olivera <julio.olvr@...>
Date: 2013-04-24T13:09:21+09:00
Subject: Re: what is the $- magic global?

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If you try it on http://repl.it/, $- immediately returns nil. Perhaps on
irb the interpreter is waiting for more input? I can't test it right now,
but what happens if you write something like the following?

> $-x =3D 42
> $-
> x

Julio
@_joliv <http://twitter.com/_joliv>


On Wed, Apr 24, 2013 at 1:00 AM, tamouse mailing lists <
tamouse.lists@gmail.com> wrote:

> 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 $=3D 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 =E2=86=92 String Synonym for $/
> $-F =E2=86=92 String Synonym for $;
> $-a =E2=86=92 Object True if the -a option is specified on the command li=
ne
> $-d =E2=86=92 Object Synonym for $DEBUG.
> $-i =E2=86=92 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 =E2=86=92 Array Synonym for $:
> $-l =E2=86=92 Object Set to true if the -l option (which enables line-end
> processing) is present on the command line.
> $-p =E2=86=92 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 =E2=86=92 Object Synonym for $VERBOSE.
> $-w =E2=86=92 Object Synonym for $VERBOSE.
> $-W =E2=86=92 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....
>
>

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<div dir=3D"ltr">If you try it on=C2=A0<a href=3D"http://repl.it/">http://r=
epl.it/</a>, $- immediately returns nil. Perhaps on irb the interpreter is =
waiting for more input? I can&#39;t test it right now, but what happens if =
you write something like the following?<div style>

<br></div><div style>&gt; $-x =3D 42</div><div style>&gt; $-</div><div styl=
e>&gt; x</div></div><div class=3D"gmail_extra"><br clear=3D"all"><div><div =
dir=3D"ltr">Julio<div><a href=3D"http://twitter.com/_joliv" target=3D"_blan=
k">@_joliv</a></div>

</div></div>
<br><br><div class=3D"gmail_quote">On Wed, Apr 24, 2013 at 1:00 AM, tamouse=
 mailing lists <span dir=3D"ltr">&lt;<a href=3D"mailto:tamouse.lists@gmail.=
com" target=3D"_blank">tamouse.lists@gmail.com</a>&gt;</span> wrote:<br><bl=
ockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #=
ccc solid;padding-left:1ex">

<div class=3D"im">On Tue, Apr 23, 2013 at 9:21 PM, Matthew Kerwin &lt;<a hr=
ef=3D"mailto:lists@ruby-forum.com">lists@ruby-forum.com</a>&gt; wrote:<br>
&gt; Also: I&#39;m aware of bash&#39;s $- options description, but that doe=
sn&#39;t seem<br>
&gt; relevant in this case; bash&#39;s $- is a simple string, and doesn&#39=
;t have<br>
&gt; any magic attached.<br>
&gt;<br>
&gt; I know that perl and ruby both have a similarly-defined $+ magic<br>
&gt; variable. =C2=A0Perl also has a $- (&quot;The number of lines left on =
the page of<br>
&gt; the currently selected output channel.&quot;) but I doubt there&#39;s =
a<br>
&gt; correlation with ruby&#39;s, because perl&#39;s is a simple integer, a=
nd is<br>
&gt; related to $~ and $=3D which are completely different between the two<=
br>
&gt; languages.<br>
&gt;<br>
&gt; I&#39;ve also encountered perl&#39;s @-/@+ match offsets, but can&#39;=
t see how<br>
&gt; they&#39;d be relevant.<br>
<br>
</div>Hummm... I&#39;m flummoxed as well. I just went through the newest<br=
>
Programming Ruby book (beta 2) and cannot find anything referencing<br>
$-. It lists these:<br>
<br>
$-0 =E2=86=92 String Synonym for $/<br>
$-F =E2=86=92 String Synonym for $;<br>
$-a =E2=86=92 Object True if the -a option is specified on the command line=
<br>
$-d =E2=86=92 Object Synonym for $DEBUG.<br>
$-i =E2=86=92 String If in-place edit mode is enabled (perhaps using the -i=
<br>
command-line option), $-i holds the extension used when creating the<br>
backup file.<br>
$-I =E2=86=92 Array Synonym for $:<br>
$-l =E2=86=92 Object Set to true if the -l option (which enables line-end<b=
r>
processing) is present on the command line.<br>
$-p =E2=86=92 Object Set to true if the -p option (which puts an implicit<b=
r>
while gets...end loop around your program) is present on the command<br>
line.<br>
$-v =E2=86=92 Object Synonym for $VERBOSE.<br>
$-w =E2=86=92 Object Synonym for $VERBOSE.<br>
$-W =E2=86=92 Object Return the value set by the -W command-line option.<br=
>
<br>
and this:<br>
<br>
&quot;a global variable name can be formed using $- followed by a single<br=
>
letter or underscore&quot; [p 318 in PDF]<br>
<br>
but no bare $- variable....<br>
<br>
</blockquote></div><br></div>

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