Access element of an array

In this most simple example we have an array called @names and we try to print the first element in the array by accessing @names[0];.

examples/array_index1.pl

use warnings;
use strict;
use 5.010;

my @names = qw(Foo Bar);
say @names[0];

The output looks like this:

Scalar value @names[0] better written as $names[0] at array_index1.pl line 6.
Foo

So we get the correct value printed, but we also get a warning.

In Perl, when you talk about a whole array or about a slice of an array you use the @ sigil, but when you try to access a single element of an array you need to use the $ sigil. So the proper way to access the first element of the @names array is to use $names[0].

Array element in dereference

In the second example we have slightly more complex expression,

examples/array_index2.pl

use warnings;
use strict;

sub f {
    my @prevCommands = @{ @_[0] };
}

Running this code we only get the warning but no output. The function does not even get executed, the warning is already emitted.

Scalar value @_[0] better written as $_[0] at array_index2.pl line 5.

Here too, instead of @_[0] we should have written $_[0]. Not to be confused with $_ the default variable of Perl that does not have a square-bracket nor curly braces after it.

Correct way to access elements of an array in Perl

The correct way can be seen in this code:

examples/array_index.pl

use warnings;
use strict;
use 5.010;

my @names = qw(Foo Bar);
say $names[0];

sub f {
    my @prevCommands = @{ $_[0] };
}

Comments

I've always viewed it as telling perl what I want returned. If I just want a single element of an array then I tell Perl I wan a scalar, $. If I want the whole array or a slice I tell Perl I want an array, @. And likewise if I want the whole hash...