The first is being evaluated in a list context, because print takes a list, but the second is evaluted in a scalar context because you're concatenating this. In a scalar context, a list evaluates to the number of elements it contains.

If you change the contexts in your examples, you'll get the opposite results: 

perl -e 'print scalar(my ($rec) = undef);'
perl -e 'print "return=",(my ($rec) = undef);'

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The first explicitly asks for a scalar context, and prints 1. The second stays in print's list context and so prints nothing (well, just return=).

In reply to Re: undef var by sgifford
in thread undef var by aapada

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