$/ is the input record separator. The output record separator is $\. See The parable of the falling droplet.

Also, the default value of $\ is undef (meaning that nothing will be automatically appended to each printed line). If you set $\ as shown, you should omit the trailing "\n":

{
    local $\ = "\r\n";
    print "Win/DOS line ending";
}
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— otherwise, you will get "\n\r\n" printed at the end of the string.

Hope that helps,