Now I am going to show you some more advanced ways of working with subroutines. Below are a few examples on passing variables through subroutine calls. These really come in handy when creating error handling routines.

1. &getIP;
2. &display;($IP);
   
3. sub GetIP {
4. $IP = $ENV{'REMOTE_ADDR'};
5. }
   
6. sub display {
7. print "Your IP Address: @_\n";
8. }

The following will do the same thing:

1. &getIP;
2. &display;($IP);
   
3. sub GetIP {
4. $IP = $ENV{'REMOTE_ADDR'};
5. }
   
6. sub display {
7. local($i) = @_;
8. print "Your IP Address: $i\n";
9. }

Here is an example of where it would come in handy for passing error messages.

1. open(FILE,"file.txt") || &error;("Error:" $file);;
2. @file = <FILE>;
3. close(FILE);
   
   Now lets pretend file.txt does not exist, thus it can't be opened! The code, || = Or. So perl will try opening the file, OR it will execute the error subroutine if the file is not found.
   
   
4. sub error {
5. local($error) = @_;
6. print "$error\n";
7. }