Socket Programming in Perl
Using sockets in Perl, it is possible to communicate to a server using a client
program. Here, I will explain how using sockets a client program can communicate
to a server. The client program is run at the client-side while the server
program runs in the Internet. For testing the program, you can run it on a local
For this example, I will use the IO::Socket::INET Perl module
which is included with most Perl distributions. If you don't have the module,
get it from http://www.cpan.org/modules/index.html.
We will use the User Datagram Protocol (UDP) to connect to the server. The
module also supports the TCP protocol.
Client Program :
First of all we need to create the socket. The socket is created easily
by initializing a new instance of the IO::Socket::INET object like this :
MySocket, thus inherits all the properties and methods of the IO::Socket::INET
The various key-value pairs we have passed to the newly created
object are as follows :
Apart from the key-value pairs we have passed, there are
many other parameters that can be passed to the object. We are not concerned of
them here. You can find details of accepted key-value pairs in the module's
- PeerPort = 1234; The PeerPort can be a number or symbolic service name.
- Proto = 'udp'; We use the UDP protocol. The TCP protocol is also supported.
If Proto is not provided, it will try to derive it from the service name
(PeerPort). If this fails, 'tcp' is assumed as the Proto.
- PeerAddr = 'localhost'. The PeerAddr can be a host name or an IP address.
Here we are tesing the programs locally so we have used 'localhost'. If the
server program is running in the Internet then you must use it's IP address or
Now that we have created the socket, we can now send a
message to the server using the object's send() method :
Thus we have created the client program. Now let us create the server program,
that will display the messages that the client has sent.
In the server program also, we create the socket in a
similar manner :
Notice that in the server program we have passed only two key-value pairs :
Now after creating
the socket, we can now receive messages sent by the client using the object's
recv() method :
- LocalPort = 1234; this is the local host bind port and should be same as the
PeerPort value passed in the client program.
- Proto = 'udp'; Protocol used in communication with client, it should be same
as the Proto value passed in the client program.
Here the first argument passed to the recv() method must be '$text', the second
argument passed indicates the maximum number of bytes the server should receive.
After receiving the message, it can be easily displayed using the $text
Thus we have created the server program. Now the client can
communicate with server using a socket. Note that for the server to receive
messages from the client, it(server) should be running while the message is
being sent by the client.
Client program code :
We have refined the client program so that it accept inputs from the keyboard
which is transmitted to the server. A double return(pressing enter/return twice)
will exit the client program.
Server program code :
We have refined the server program so that as and when the client sends a
message, the server keeps displaying it. When the client sends a blank message,
the server program terminates.
Thus we have learned how to communicate
to a server from a client using sockets.
© 2002 Premshree Pillai.