What does die do?
When you want to signal that something went slightly wrong, you call the warn function.
When you want to signal that something went terribly wrong, and you want to throw in the towel, you call die.
People reading Perl code are quite familiar with the die. One of the know expression is the open or die style code to open a file.
A call to die will print out the given string to the standard error (STDERR) and then quit the program.
It has the same extra feature as warn has, that if the string you passed to it does not end with a newline \n, perl automatically includes the name of the file and the line number where the die was called.
This can help later finding the source of the problem.
While in simple scripts it usually does not matter, die actually throws an exception. In simple scripts you probably won't have any special code to catch these exceptions. In those cases you basically use die instead of calling warn and then >exit.
In bigger applications, when you start writing modules, you will probably already want to really throw exceptions, and then capture them using eval. We'll deal with that in another article.
Collecting die calls
In a slightly more advanced way, Perl provides a signal handle for die, just as it does for warn. The big difference is that the signal handler that collects the die call does not stop your script from dieing. It is only interesting in the cases where you already catch the exception (e.g. using eval) and you are interested in finding cases when someone caught an exception, but did not handle it well. For those cases see the article about capturing die calls.