Learning Perl, 5th Edition

The Naked Block Control Structure

The so-called naked block is one without a keyword or condition. That is, suppose you start with a while loop, which looks something like this:

while (condition) {
  body;
  body;
  body;
}

Now, take away the while keyword and the conditional expression, and you’ll have a naked block:

{
  body;
  body;
  body;
}

The naked block is like a while or foreach loop, except that it doesn’t loop; it just executes the body of the loop once, and it’s done. It’s an un-loop!

You’ll see in a while that there are other uses for the naked block, but one of its features is that it provides a scope for temporary lexical variables:

{
  print "Please enter a number: ";
  chomp(my $n = <STDIN>);
  my $root = sqrt $n;  # calculate the square root
  print "The square root of $n is $root.\n";
}

In this block, $n and $root are temporary variables scoped to the block. As a general guideline, all variables should be declared in the smallest scope available. If you need a variable for just a few lines of code, you can put those lines into a naked block and declare the variable inside that block. Of course, if you would need the value of either $n or $root later, you would need to declare them in a larger scope.

You may have noticed the sqrt function in that code and wondered about it—yes, it’s a function we haven’t shown before. Perl has many built-in functions that are beyond the scope of this book. When you’re ready, check the perlfunc manpage to learn about more of them.