In this case, the << marks a here-doc, and '}' is the marker. This is equivalent: 

$_ = <<'END_OF_STRING';

if ($some_condition) {
        return $X;
} else {
        return $Y;
END_OF_STRING

die "not reached";

[download]

You can find here-docs documented in perlop.

In reply to Re^4: Can't happen bug follow-up -- Can an if/else be bypassed? by kyle
in thread Can't happen bug follow-up -- Can an if/else be bypassed? by Your Mother

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