The following is even simpler:

my $pkg = 'Foo';
my $foo = do { local $/; eval "<${pkg}::DATA>" };
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The following is a version that doesn't use eval EXPR (faster, safer):

my $pkg     = 'Foo';
my $data_fh = do { no strict 'refs'; *{"${pkg}::DATA"} };
my $foo     = do { local $/; <$data_fh> };
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And if you want to cut your memory usage in half, use the following:

my $pkg = 'Foo';
my $data_fh; { no strict 'refs'; $data_fh = *{"${pkg}::DATA"}; }
my $foo;     { local $/; $foo = <$data_fh>; }
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You could even combine the two blocks.