#!/usr/bin/perl 

# untested!

use strict;
use warnings;
use feature "say";

sub write_file
{
    my ($fn,$content)=@_;
    open my $f,'>',$fn or die "Could not open $fn: $!";
    say $f $content;
    close $f;
}

sub export
{
    my $number=shift;
    write_file("/sys/class/gpio/export",$number);
}

sub direction
{
    my ($number,$dir)=@_;
    write_file("/sys/class/gpio/gpio$number/direction",$dir);
}

sub write_value
{
    my ($number,$level)=@_;
    write_file("/sys/class/gpio/gpio$number/value",$level);
}

sub read_file # unused
{
    open my $f,'<',$fn or die "Could not open $fn: $!";
    my $line=<$f>;
    close $f;
    chomp $line;
    return $line;
}

sub read_value # unused
{
    my $number=shift;
    return read_file("/sys/class/gpio/gpio$number/value");
}

# all of the functions above could move to a module 

export(20);
direction(20,"out");

while (1) {
    write_value(20,0);
    say "on";
    sleep 1;
    write_value(20,1);
    say "off";
    sleep 1;
}