die( ) is usually used to abort the flow of the program if something goes wrong. For example, this common idiom is used when opening files:

open FILE, "foo" or die "Cannot open 'foo' for reading: $!";

If the file cannot be opened, the script will die( ): script execution is aborted, the reason for death is printed, and the Perl interpreter is terminated.

You will hardly find any properly written Perl scripts that don't have at least one die( ) statement in them.

CGI scripts running under mod_cgi exit on completion, and the Perl interpreter exits as well. Therefore, it doesn't matter whether the interpreter exits because the script died by natural death (when the last statement in the code flow was executed) or was aborted by a die( )statement.

Under mod_perl, we don't want the process to quit. Therefore, mod_perl takes care of it behind the scenes, and die( ) calls don't abort the process. When die( ) is called, mod_perl logs the error message and calls Apache::exit( ) instead of CORE::die( ). Thus, the script stops, but the process doesn't quit. Of course, we are talking about the cases where the code calling die( ) is not wrapped inside an exception handler (e.g., an eval { } block) that traps die( ) calls, or the $SIG{__DIE__} sighandler, which allows you to override the behavior of die( ) (see Chapter 21). Section 6.13 at the end of this chapter mentions a few exception-handling modules available from CPAN.