Learning Perl, Fourth 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;
    }

Remove 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 executes the body of the loop once, and it’s done. It’s an un-loop!

You’ll see other uses for the naked block, but one of its features is providing 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 a few lines of code, you can put those lines into a naked block and declare the variable inside that block. If you need the value of $n or $root later, you will need to declare them in a larger scope.

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