possible mis-use of single-quoting if you are on W32? Or, try:

#!/usr/bin/perl -l
use strict;
use warnings;

my $n = shift;                # assign the number provided as an argue
+ment to  $n
die q{Please provide a positive number.} if ($n < 0); # not negative 
print q{*} x $n;             # print "*" $n times followed by newline 
+(the shebang's -l switch
if ($n >1) { 
    foreach (2 .. $n - 1) {               # print second line .. next 
+to last line
       print q{*}, q{ } x ($n - 2), q{*}; # with $n-2 spaces (first & 
+last postions are *
    } 
    print "*" x $n ; 
}
[download]

Tested on *nix and W2k