First of all, it would be simpler to avoid misleading the user by using a hack to circumvent strictures.

sub input_pin {
   my $name = sprintf( "Device::BCM2835::RPI_V2_GPIO_P1_%02d", $_[0] )
+;
   no strict "refs";
   return $name->();
}
[download]

But consider the following version:

my @input_pin;
for ( @Device::BCM2835::EXPORT_OK ) {
   next if !/^RPI_V2_GPIO_P1_(\d+)\z/;
   my $pin = 0 + $1;
   my $val = do { no strict "refs"; "Device::BCM2835::$_"->() };
   $input_pin[ $pin ] = $val;
}
[download]

This version allows us to do

$input_pin[3]
$input_pin[5]
$input_pin[7]
...
[download]

instead of the slower

input_pin(3)
input_pin(5)
input_pin(7)
[download]

So what if it's not the simplest?

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Update: The point of the first half is that using no strict version is simpler, but it originally said the opposite! woops. And sprintf was misspelled.