Is there a way to turn the list context returned by map and grep into a scalar context?

Yes, by forcing scalar context or using the scalar() function, but seeing as how that's not what you want, an array slice will just have to do

perl -le 'print +(grep /\d/, qw/foo b4r b4z quux/)[0]'
b4r
[download]

See. perldata for more info on slicing.
HTH

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broquaint