While this isn't a book about Perl, you should at least be familiar with how Perl works. So, let's go through the different sections of the presidents.pl program and describe what they do:

  • #!/usr/bin/perl

    This specifies the path to the Perl program on the computer.

  • use DBI;
    use strict;

    The use DBI line means use DataBase Interface. It refers to the Perl module that interacts with your MySQL database. You might think of this module as a MySQL client that speaks Perl. It does most of the things the MySQL client does, but through Perl.

    The use strict line is a matter of personal preference and programming etiquette. Variables are "containers" in a Perl script that hold specific information. In Perl, using the strict mode requires you to reserve all variables before they are used. The next bullet shows how this works.

  • # database information
    my $db="us_presidents";
    my $host="localhost";
    my $port="3306";
    my $userid="marty";
    my $passwd="watch4keys";
    my $connectionInfo=
    "DBI:mysql:database=$db;$host:$port";

    Like the comment says (what comes after a # character is a comment—a note in the program to be read by people, not the computer), this is information about the database.