meaning of '@' sigil on a hash?

I have this code and wonder why it works this way with a '@' preceding the hash:

#!/usr/bin/perl -w

use strict;
use Data::Dumper;

my %hash;
my @keys = qw ( one two three );
my @values = qw ( 1 2 3 );

#  What's with the @ symbol and not a $?
@hash{@keys} = @values;

print Dumper \%hash;
[download]

I'd expect it to be as below:

#!/usr/bin/perl -w

use strict;
use Data::Dumper;

my %hash;
my @keys = qw ( one two three );
my @values = qw ( 1 2 3 );

#  I thought it would need a $!
$hash{@keys} = @values;

print Dumper \%hash;
[download]

Why do you need the '@' preceding the hash name and not a '$'?

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Re: meaning of '@' sigil on a hash?
by plobsing (Friar) on Dec 08, 2007 at 17:57 UTC

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Re: meaning of '@' sigil on a hash?
by shmem (Canon) on Dec 08, 2007 at 18:18 UTC

Why do you need the '@' preceding the hash name and not a '$'?

Because you are accessing the hash in list context. Did you try it with a $ as sigil? Doing so will result in

$VAR1 = {
          '3' => 3
        };
[download]

because $hash{@keys} is a scalar. So, the array @keys is evaluated in scalar context, which yields 3 (three elements). The scalar context on the left of the assignment enforces scalar context on the right, so that's also 3 (three elements.)

--shmem

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}

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Re: meaning of '@' sigil on a hash?
by Burak (Chaplain) on Dec 08, 2007 at 18:28 UTC

@hash{@keys} = @values;

$hash{@keys} = @values;

@array[0..4] = qw(a b c d e);
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Re: meaning of '@' sigil on a hash?
by ikegami (Pope) on Dec 08, 2007 at 19:19 UTC

In Perl5, the sigil represents how the variable should be treated. It does not represent the type of the variable. So just like $ can be used by scalar, arrays and hashes, @ can be used by arrays and hashes.

	select element	select elements (slice)	all keys	all values	all keys & values
scalar	`$scalar`
array	`$array[$i]`	`@array[@i]`	`(0..$#array)`	`@array`
hash	`$hash{$i}`	`@hash{@i}`	`keys(%hash)`	`values(%hash)`	`%hash`
list		`(...)[@i]`

This is all documented in perldata, including slices.

Update: Reordered the columns.

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Re: meaning of '@' sigil on a hash?
by bradcathey (Prior) on Dec 09, 2007 at 00:17 UTC

awohld, glad to have you around, but help those who will be searching your nodes in the future, by Choosing a Good, Descriptive Title.

—Brad
"The important work of moving the world forward does not wait to be done by perfect men." George Eliot

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meaning of '@' sigil on a hash?

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