Basically this reads set $x to 5 if $x is false (0 or undef)

$x = 0;
$x = $x || 5;
# prints 5
print $x;


$x = 4;
$x = $x || 5;
$prints 4
print $x;

$x = $x || 5;
# prints 5
print $x;
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