in reply to Any downsides to this slurp idiom?

If the file you're slurping has any size, you're better to do:

my $s; do{ local( @ARGV, $/)='big.file'; $s = <> };
my $s = do{ local( @ARGV, $/)='big.file'; <> };

As the latter makes two copies of the file. One in a temporary, and then a copy in $s.

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