Subroutines

Perl defines subroutines in the following form:
 sub SUBNAME { 
                STATEMENTS; 
        }
Subroutines are invoked in this way:
        &SUBNAME(arg1,arg2,etc); 
        # - or - (if the subroutine takes no arguments. 
        &SUBNAME; 
        # return values are used just like any other value  
        $returnvalue = &SUBNAME(@values);

Example

        # define an error  routine: 
        sub error { 
                ($message) = @_; 
                print("<b>ERROR:<b>", 
                        $message, 
                        "<p>Contact the author of the previous page for assistance\n"); 
                exit(0); 
        } 
        if ( ! $recipient ) { 
                # the form did not have a to field 
                # modify this text appropriately 
                &error("No Return Address"); 
        }

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