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

##</code><code>##

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;
}

##</code><code>##

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

##</code><code>##

input_pin(3)
input_pin(5)
input_pin(7)