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Perl Language Reference Manual
by Larry Wall and others
Paperback (6"x9"), 724 pages
ISBN 9781906966027
RRP £29.95 ($39.95)

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20.5.1 A Simple Client

Here's a client that creates a TCP connection to the "daytime" service at port 13 of the host name "localhost" and prints out everything that the server there cares to provide.

#!/usr/bin/perl -w
use IO::Socket;
$remote = IO::Socket::INET->new(
                    Proto    => "tcp",
                    PeerAddr => "localhost",
                    PeerPort => "daytime(13)",
        or die "cannot connect to daytime port at localhost";
while ( <$remote> ) { print }

When you run this program, you should get something back that looks like this:

Wed May 14 08:40:46 MDT 1997

Here are what those parameters to the new constructor mean:

This is which protocol to use. In this case, the socket handle returned will be connected to a TCP socket, because we want a stream-oriented connection, that is, one that acts pretty much like a plain old file. Not all sockets are this of this type. For example, the UDP protocol can be used to make a datagram socket, used for message-passing.
This is the name or Internet address of the remote host the server is running on. We could have specified a longer name like "www.perl.com", or an address like "". For demonstration purposes, we've used the special hostname "localhost", which should always mean the current machine you're running on. The corresponding Internet address for localhost is "127.1", if you'd rather use that.
This is the service name or port number we'd like to connect to. We could have gotten away with using just "daytime" on systems with a well-configured system services file,[FOOTNOTE: The system services file is in /etc/services under Unix] but just in case, we've specified the port number (13) in parentheses. Using just the number would also have worked, but constant numbers make careful programmers nervous.

Notice how the return value from the new constructor is used as a filehandle in the while loop? That's what's called an indirect filehandle, a scalar variable containing a filehandle. You can use it the same way you would a normal filehandle. For example, you can read one line from it this way:

$line = <$handle>;

all remaining lines from is this way:

@lines = <$handle>;

and send a line of data to it this way:

print $handle "some data\n";
ISBN 9781906966027Perl Language Reference ManualSee the print edition