use strict;
use warnings;

my (@grid, $top, $bottom, $left, $right);

while (<DATA>) {
    chomp;
    push @grid, [split / /];
}

$top = 0;
$bottom = $#grid;
$left = 0;
$right = $#{$grid[0]};

while (1) {
    print $_ for @{$grid[$top]}[$left..$right];
    last if ++$top > $bottom;
    
    print $grid[$_][$right] for $top..$bottom;
    last if --$right < $left;

    print $_ for @{$grid[$bottom]}[reverse $left..$right];
    last if --$bottom < $top;

    print $grid[$_][$left] for reverse $top..$bottom;
    last if ++$left > $right;
}

__DATA__
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EDIT: Whose doesn't work for 4 rows, ikegami? I tested mine with a number of different configurations, including several with 4 rows, and it seemed to work just fine.