Very simple HTTP observation script. writen at 2017/06/16 in "Perl Entrance in Tokyo", after party.

http-ob.pl

#!/usr/bin/env perl
# 2018/06/16
# とても素朴なURL外形監視

use strict;
use warnings;

use Net::SMTP;
use HTTP::Tiny;
use Data::Dumper;

my $from_address = 'foo@example.com';
my $to_address   = 'bar@example.com';
#my $observation_url = "http://www.yahoo.co.jp/";
my $observation_url = "http://www.yahoo.co.jp/not_found";

my $http     = HTTP::Tiny->new;
my $response = $http->get($observation_url);

# ハッシュリファレンスで返されるレスポンスの構造を Data::Dumper で調べる
# print Dumper($response);
# my $date = $response->{headers}->{date};
# print "Yahoo Server Date is $date\n";

# デーモン的にやるのであれば、原始的なループ
# while (1) {
#     # 処理
#     sleep 300;
# }

# cron 的にやるのであれば単発で
if ( $response->{status} eq '200' ) { # == 200 でも良い
    print "OK\n";
} else {
    print "$observation_url NG. status is $response->{status}\n";
    mailsend(
        $from_address,
        $to_address,
        "$observation_url NG. status is $response->{status}. please check.\n",
    );
}

sub mailsend {
    my ($from, $to, $body) = @_; # この書き方は次回やります
    my $smtp = Net::SMTP->new('localhost');
    $smtp->mail($from);
    if ($smtp->to($to)) {
        $smtp->data();
        $smtp->datasend("From: $from\n");
        $smtp->datasend("To: $to\n");
        $smtp->datasend("Subject: observation alert");
        $smtp->datasend("\n");
        $smtp->datasend("$body\n");
        $smtp->dataend();
    } else {
        print "Error: ", $smtp->message();
    }
    $smtp->quit;
}