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Posted by John W. Krahn on April 1, 2008, 10:45 pm
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David Harmon wrote:
> On Mon, 31 Mar 2008 23:23:25 +0200 in comp.lang.perl.misc, Gunnar
>> I do, I hope. :)
>>
>> foreach my $num ( 0 .. 0b11111 ) {
>> local *_ = \ sprintf '%05b', $num;
>
> What is *_ ? It looks like one of those magic perl variables, but
> I don't find any documentation on it.
It is a typeglob. It means that you want all of the _ variables to have
a local value. See the "Typeglobs and Filehandles" section of perldata.pod.
perldoc perldata
John
--
Perl isn't a toolbox, but a small machine shop where you
can special-order certain sorts of tools at low cost and
in short order. -- Larry Wall
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Posted by Tad J McClellan on April 1, 2008, 11:34 pm
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> On Mon, 31 Mar 2008 23:23:25 +0200 in comp.lang.perl.misc, Gunnar
>>I do, I hope. :)
>>
>> foreach my $num ( 0 .. 0b11111 ) {
>> local *_ = \ sprintf '%05b', $num;
>
> What is *_ ?
It is a typeglob of the variables named underscore.
> It looks like one of those magic perl variables,
^^^
^^^
It is many of those magic perl variables.
It is $_ and @_ and _ and ...
> but
> I don't find any documentation on it.
See the "Typeglobs and Filehandles" section in perldata.pod.
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.noitatibaher0cmdat/"
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Posted by Ben Morrow on April 2, 2008, 12:58 am
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Quoth "Newsgroup only please, address is no longer replyable."
> On Mon, 31 Mar 2008 23:23:25 +0200 in comp.lang.perl.misc, Gunnar
> >I do, I hope. :)
> >
> > foreach my $num ( 0 .. 0b11111 ) {
> > local *_ = \ sprintf '%05b', $num;
>
> What is *_ ? It looks like one of those magic perl variables, but
> I don't find any documentation on it.
What noone has said yet is why Gunnar used it. Due to a rather nasty bug
in perl, under certain rather obscure circumstances[0] $_ doesn't
localise properly, so if you need to do so it is safer to localise the
whole of *_. Unfortunately, besides being ugly, this means you lose your
sub arguments (and the magic stat filehandle, of course, but that's
likely less important); personally I would always rather use a for loop
over one element
for (sprintf '%05b', $num) {
or, with 5.10, either 'given' (like for, but gives scalar context to its
argument) or 'my $_'. None of these suffer from the bug.
Ben
[0] If $_ is an alias to an element of a tied hash or array, the value
of that element will be localised along with $_. A simple example is
use Tie::Hash;
tie my %h, 'Tie::StdHash';
$h = 1;
for ($h) {
local $_ = 2;
print $h; # 2, but should be 1
}
print $h; # back to 1 again
This is only really important if you call external code in the scope of
the 'local': if that code reads the hash, it will be surprised to find
the values have changed.
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Posted by Abigail on April 2, 2008, 8:33 am
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David Harmon (source@netcom.com) wrote on VCCCXXVIII September MCMXCIII
[] On Mon, 31 Mar 2008 23:23:25 +0200 in comp.lang.perl.misc, Gunnar
[] >I do, I hope. :)
[] >
[] > foreach my $num ( 0 .. 0b11111 ) {
[] > local *_ = \ sprintf '%05b', $num;
[]
[] What is *_ ? It looks like one of those magic perl variables, but
[] I don't find any documentation on it.
It's a silly attempt to obfuscate the code.
It's much better written as:
foreach (0 .. 0b11111) {
my $_ = sprintf '%05b' => $_;
tr _01_NY_;
say "$::_:$_";
}
No silly typeglobs needed.
Abigail
--
map=chr}map$=+$]..3*$=/2;
print "$J$u$s$t $a$n$o$t$h$e$r $P$e$r$l $H$a$c$k$e$r\n";
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Posted by Frank Seitz on April 2, 2008, 8:49 am
Please log in for more thread options Abigail wrote:
>
> It's a silly attempt to obfuscate the code.
>
> It's much better written as:
>
> foreach (0 .. 0b11111) {
> my $_ = sprintf '%05b' => $_;
> tr _01_NY_;
> say "$::_:$_";
> }
Nice.
> No silly typeglobs needed.
You forgot
use 5.10.0;
Frank
--
Dipl.-Inform. Frank Seitz; http://www.fseitz.de/
Anwendungen für Ihr Internet und Intranet
Tel: 04103/180301; Fax: -02; Industriestr. 31, 22880 Wedel
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