$csv and $xls = $csv;

Here and is used for control flow. It separates statements (or expressions) which are conditionally evaluated from left to right. The first is simply $csv and so the subsequent statement is only evaluated (and therefore executed) if this first expression is true. You can see then that the whole line is equivalent to writing

$xls = $csv if $csv;

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In reply to Re: Confused by a couple of idioms by hippo
in thread Confused by a couple of idioms by nysus

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