See How do I shuffle an array?.

@lines = <IN>;
shuffle(@lines);
print OUT @lines;

# or if 'shuffle' returns the shuffled list

print OUT shuffle(<IN>);
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As far as moving elements from one place to another, just move them around, or use splice if you need some more "serious" movements:

($lines[param('from')], $lines[param('to')]) =
   ($lines[param('to')], $lines[param('from')]);
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