$str1 = "Some String";
$str2 = 'Some String';
if( $str1 eq $str2 ) { 
    print ">>$str1<< is identical to >>$str2<<\n"; 
}

##</code><code>##

$str1 = "'Some String'"; 
$str2 = '"Some String"';
if( $str1 ne $str2 ) { 
    print ">>$str1<< is different to >>$str2<<\n";
}
...
>>'Some String' is different to >>"Some String"<<