http://www.perlmonks.org?node_id=487213

A recursive solution:

```use strict;
use warnings;

my \$n = shift;
my \$count = 1;
my @matrix;

push @matrix, [(0)] for (1..\$n);
buildRing (0, \$n - 1);
my \$width = length sprintf ("%s", '' . \$count);
my \$format = "%\${width}d";
print "" . (join " ", map {sprintf \$format, \$_} @{\$matrix[\$_]}) . "\n"
+ for (0..(\$n-1));

sub buildRing
{
my (\$first, \$last) = @_;
\$matrix[\$first][\$_] = \$count++ for (\$first..\$last);
\$matrix[\$_][\$last] = \$count++ for ((\$first+1)..\$last);
\$matrix[\$last][\$last-\$_+\$first-1] = \$count++ for (\$first..\$last-1);
for (\$_ = --\$last; \$_ > \$first; --\$_)
{\$matrix[\$_][\$first] = \$count++}
\$matrix[\$first][\$last] = \$count if (++\$first == \$last);
buildRing (\$first, \$last) if (\$first<\$last);
}
```use strict;
use warnings;

my \$n = shift || 5;
my (\$count, \$first, \$last) = (1, 0, \$n - 1);
my @matrix;

push @matrix, [(0)] for (1..\$n);
{
\$matrix[\$first][\$_] = \$count++ for (\$first..\$last);
\$matrix[\$_][\$last] = \$count++ for ((\$first+1)..\$last);
\$matrix[\$last][\$last-\$_+\$first-1] = \$count++ for (\$first..\$last-1);
for (\$_ = --\$last; \$_ > \$first; --\$_)
{\$matrix[\$_][\$first] = \$count++}
\$matrix[\$first][\$last] = \$count if (++\$first == \$last);
redo unless \$first >= \$last;
}

my \$width = (int log \$count) - 1;
print "" . (join " ", map {sprintf "%\${width}d", \$_} @{\$matrix[\$_]}) .
+ "\n" for (0..(\$n-1));
```\$n=shift;(\$c,\$f,\$l,@m)=(1,0,--\$n);