The User Defined Function is a set of code that will be executed when the function is called. In Perl user defined function does'nt require arguments, but if needed arguments can be passed.

    sub function_name
     {
      function_body
     }

In the above syntax "function_name" specifies a unique name for the function, in the "function body" contains a set of code to be executed when there is a function call.

    #! C:\programfiles\perl\bin\perl
    print "content-type: text/html\n\n";
    sub present 
     {
      print "The Key is present.\n";
     }
    sub notpresent
     {
      print "The Key not present.\n";
     }
    %emp = ('empno' => '12422' , 'empname' => 'Kate Anderson', 
            'empph' => '9167552148', 'empcode' => 'ADS212');
    if (exists $emp{'empcode'})
     {
      present();
     }
    else
     {
      notpresent();
     }

    The Key is present. 

In the above example using exists() function a value is checked in an array, if present, it calls a function "present()" otherwise, it calls a function "notpresent()". Since the "empcode" is present, it displays "The Key is present".