You have specified that there is no mistake in the Server Side Code. But I am sure that There is small mistake you have done in the server Side code only.

sub handle_connection
{
        my $x = shift;
        my $sz = <$x>;
        print $x "Testing\n";
}
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Insted do as follows

sub handle_connection
{
        my $x = shift;
        
        while ( <$x> ) {
          print $x "Testing\n";
        }
        
}
[download]

The mistake what you have done is, You are getting only one line from the client ( But you are writting 100 lines from clinet side ). Once you get a single line from client you are closing the Client Side Socket Filehandle. So next time when the client tries to write another line into the server the broken connectio happened So you need to be very careful in handling the connection.

Also It is advisable to use select function in server side program so that we can check all the events happening in both server and cient file handles.

also there are some mistakes in client and Server for example in server side you are getting the port number as a command line arguement where as in client side the port is hard coded.