And if the othe various posts haven't illuminated yet, it's worth walking through some other examples step by step. (Including strict and warnings.)

Using all fully qualified globals:

use strict;
use warnings;

$main::var = 1;
{
    $main::var = 2;
    print $main::var, "\n";    # prints 2
}
print $main::var, "\n";        # also prints 2
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Declaring within the block:

use strict;
use warnings;

$main::var = 1;
{
    our $var = 2;
    print $var, "\n";    # prints 2
}
print $main::var, "\n";        # also prints 2
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Declaring within the block and trying to use unqualified later (on line 9) causes a compile-time error under strict -- the "our" only has its effect of allowing use of the variable name without fully qualifiying it while within the block:

use strict;
use warnings;

$main::var = 1;
{
    our $var = 2;
    print $var, "\n";    # prints 2
}
print $var, "\n";        # also prints 2
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Typical usage "at the top" applies to the whole file:

use strict;
use warnings;

our $var = 1;
{
    $var = 2;
    print $var, "\n";    # prints 2
}
print $var, "\n";        # also prints 2
[download]