How to check if a URL is reachable in Perl?

Checking if a URL is reachable in Perl generally means verifying whether you can successfully connect to the web server and receive a valid HTTP response. Unlike simple ICMP ping, which sends network packets, URL reachability in the HTTP context usually means making an HTTP request (commonly a GET or HEAD) and inspecting the response code.

Perl offers multiple ways to achieve this, but the most straightforward and beginner-friendly approach uses LWP::UserAgent, a core module for making HTTP requests. It allows you to send requests and check the HTTP status code easily. Note that LWP::UserAgent is part of the standard Perl distribution since Perl 5.8, so you don't need extra modules beyond core installations.

Key Perl Concepts

• use strict; and use warnings; help catch common errors.
• LWP::UserAgent creates an agent object that performs HTTP communication.
• HTTP response codes: 200 OK means the URL is reachable; anything in the 400- or 500-range usually means failure.
• Sigils: $ for scalar variables (like the $response object), demonstrating typical Perl syntax.

Simple runnable example

#!/usr/bin/perl
use strict;
use warnings;
use LWP::UserAgent;

# The URL to check
my $url = 'http://www.example.com/';

# Create a user agent object
my $ua = LWP::UserAgent->new(
    timeout => 5,
    agent   => "PerlURLChecker/1.0",
);

# Make a HEAD request to check reachability (faster than GET)
my $response = $ua->head($url);

if ($response->is_success) {
    print "URL is reachable: ", $response->status_line, "\n";
} else {
    print "URL is NOT reachable: ", $response->status_line, "\n";
}

This script:

• Creates a LWP::UserAgent object with a 5-second timeout.
• Sends an HTTP HEAD request (which asks only for headers, not the full content, so it's faster).
• Checks the response status with is_success (true for HTTP 2xx codes).
• Prints a helpful message, including the full status line (e.g., "200 OK" or "404 Not Found").

Additional Tips and Gotchas

• HEAD vs GET: HEAD requests are better for checking reachability as they don't download the entire page. However, some servers may not support HEAD and may respond incorrectly, in which case switching to GET could help.
• Timeouts: Set reasonable timeouts so your script does not hang waiting for a slow or unresponsive site.
• HTTPS support: LWP::UserAgent supports HTTPS if IO::Socket::SSL is installed (usually core or easily installable). Without it, HTTPS requests will fail.
• DNS and network errors: Errors like unable to resolve the hostname or no network connectivity also count as unreachable.
• Redirects: By default, LWP::UserAgent follows up to 7 redirects, so the script will successfully report reachability if the URL redirects to a working page.

Summary

To check if a URL is reachable in Perl, using LWP::UserAgent to send a HEAD or GET request and inspecting the HTTP response is the standard, effective, and cross-platform way. It abstracts away lower-level details like socket programming and ICMP ping permissions, providing a reliable method to verify HTTP connectivity.