Learning Perl on Win32 Systems

A Slight Diversion: die

Consider the following a large footnote, but in the middle of the page.

A filehandle that has not been successfully opened can still be used without even so much as a warning throughout the program.^[67] If you read from the filehandle, you’ll get end-of-file right away. If you write to the filehandle, the data is silently discarded (like last year’s campaign promises).

Typically, you’ll want to check the result of the open and report an error if the result is not what you expect. Sure, you can pepper your program with stuff like:

            unless (open (DATAPLACE,">c:/temp/dataplace")) {
		print "Sorry, I couldn't create c:/temp/dataplace\n";
} else {
		# the rest of your program
}

But that sort of change is a lot of work. And it happens often enough for Perl to offer a bit of a shortcut. The die function takes a list within optional parentheses, spits out that list (like print) on the standard error output, and then ends the Perl program with a nonzero exit status (generally indicating that something unusual happened^[68]). So, rewriting the chunk of code above turns out to look like this:

unless (open DATAPLACE,">c:/temp/dataplace") {
		die "Sorry, I couldn't create c:/temp/dataplace\n";
}
# rest of program

But we can go even one step further. Remember that we can use the || (logical or) operator to shorten this up, as in:

open(DATAPLACE,">c:/temp/dataplace") ||
		die "Sorry, I couldn't create c:/temp/dataplace\n";

So, the die gets executed only when the result of the open is ...