Learning Perl, Fourth Edition

Answers to Chapter 6 Exercises

1. Here’s one way to do it:

       my %last_name = qw{
         fred flintstone
         barney rubble
         wilma flintstone
       };
       print "Please enter a first name: ";
       chomp(my $name = <STDIN>);
       print "That's $name $last_name{$name}.\n";

   In this one, we used a qw// list (with curly braces as the delimiter) to initialize the hash. That’s fine for this simple data set, and it’s easy to maintain because each data item is a simple given name and simple family name, with nothing tricky. If your data might contain spaces—for example, if robert de niro or mary kay place were to visit Bedrock—this method wouldn’t work as well.

   You might have chosen to assign each key/value pair separately, something like this:

       my %last_name;
       $last_name{"fred"} = "flintstone";
       $last_name{"barney"} = "rubble";
       $last_name{"wilma"} = "flintstone";

   Note that (if you chose to declare the hash with my, perhaps because use strict was in effect) you must declare the hash before assigning any elements. You can’t use my on only part of a variable, like this:

       my $last_name{"fred"} = "flintstone";  # Oops!

   The my operator works only with entire variables and never with one element of an array or hash. Speaking of lexical variables, you may have noticed the lexical variable $name is being declared inside of the chomp function call; it is fairly common to declare each my variable as it is needed, like this.

   This is another case where chomp is vital. If someone enters the five-character string "fred\n" and we fail to chomp it, we’ll ...