Rather than TCP; use UDP.

In your perl program you only need this to receive the notification:

#! perl -slw
use strict;
use IO::Socket;

socket( SOCKET, PF_INET, SOCK_DGRAM, getprotobyname('udp') ) or die "s
+ocket: $!";
bind( SOCKET, sockaddr_in( 54321, inet_aton( 'localhost' ) ) ) or die 
+$!;
my $input;

while( 1 ) {
    my $addr = recv( SOCKET, $input, 1024, 0 ) or die $!;
    my( $port, $ipbin ) = sockaddr_in( $addr );
    printf "Got '%s' from  ip:%s port:%d\n", $input, inet_ntoa($ipbin)
+, $port;
}
[download]

In your PHP program, you can use this to send the '1' or '2' when required.

The Perl script above will block at the recv until it receives the datagram from your PHP program.

... and, if there is any possibility of UDP packets coming in a “surge,” consider noting the time-of-day when the last packet was responded-to, so as to ignore subsequent packets that arrive too soon thereafter.

Good idea to switch from polling to an event-driven mechanism.

Following the TCP/IP path, you'll need a small daemon running on the RPi, e.g. by means of HTTP::Daemon. The triggers could be invoked from the PHP webpage by an HTTP GET or POST on specific URLs like http://<RPI-IP>/trigger/1 or http://<RPI-IP>/trigger/2. I assume, you want private access to the RPi? So, make sure, nobody else can run your scripts (e.g. HTTPS or SSH tunnel plus credentials).

If you already have a webserver running on the RPi, have a look at CGI/FCGI or even PSGI. The latter leads to Twiggy, Dancer, Mojolicious, etc. I have to add, that I have never run one of these on an RPi, so take this advice with a little bit of caution - they should work for a low traffic scenario though.

use IO::Socket::INET;
 
# auto-flush on socket
$| = 1;
 
# creating a listening socket
my $socket = new IO::Socket::INET (
    LocalHost => '0.0.0.0',
    LocalPort => '7777',
    Proto => 'tcp',
    Listen => 5,
    Reuse => 1
);
die "cannot create socket $!\n" unless $socket;
print "server waiting for client connection on port 7777\n";
 
while(1)
{
    # waiting for a new client connection
    my $client_socket = $socket->accept();
 
    # get information about a newly connected client
    my $client_address = $client_socket->peerhost();
    my $client_port = $client_socket->peerport();
    print "connection from $client_address:$client_port\n";
 
    # read up to 1024 characters from the connected client
    my $data = "";
    $client_socket->recv($data, 1024);
    print "received data: $data\n";
 
    # write response data to the connected client
    $data = "ok";
    $client_socket->send($data);
 
    # notify client that response has been sent
    shutdown($client_socket, 1);
}
 
$socket->close();
[download]

<?php
error_reporting(E_ALL);

echo "<h2>TCP/IP Connection</h2>\n";

/* Get the port for the WWW service. */
$service_port = 7777;

/* Get the IP address for the target host. */
$address = '82.10.291.11';

/* Create a TCP/IP socket. */
$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
if ($socket === false) {
    echo "socket_create() failed: reason: " . socket_strerror(socket_l
+ast_error()) . "\n";
} else {
    echo "OK.\n";
}

echo "Attempting to connect to '$address' on port '$service_port'...";
$result = socket_connect($socket, $address, $service_port);
if ($result === false) {
    echo "socket_connect() failed.\nReason: ($result) " . socket_strer
+ror(socket_last_error($socket)) . "\n";
} else {
    echo "OK.\n";
}

// $in = "HEAD / HTTP/1.1\r\n";
// $in .= "Host: www.example.com\r\n";
// $in .= "Connection: Close\r\n\r\n";
$in = '1234.4321.this finally works';

$out = '';

echo "Sending HTTP HEAD request...";
socket_write($socket, $in, strlen($in));
echo "OK.\n";

echo "Reading response:\n\n";
while ($out = socket_read($socket, 2048)) {
    echo $out;
}

echo "Closing socket...";
socket_close($socket);
echo "OK.\n\n";
?>
[download]

You should really try a PHP site for solutions to PHP problems, but this seems to answer the implied question.

---

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