Perl 101 (part 7) - CGI Basics - Meet Donald Duck (
Page 2 of 6 )
So far, you've used two different types of Perl
variables - the scalar and the array. However, unbeknownst to you, Perl also
comes with a third type of variable - the hash.
One of the significant
features of an array is that array values can only be accessed via a numerical
index. This implies that if you need to access an element of the array, you need
to first know its exact location in the array. Since this can get complicated
with large arrays, Perl offers you a simpler way to access array values, using
easy-to-remember "keywords" or "keys".
Thus, a hashes is a species of
Perl variable which allows you to define an array of key-value pairs. Take a
look:
%myhero = ("fname" => "Donald", "lname" => "Duck");
The Perl statement above will create a hash named "myhero",
which consists of two name-value pairs. The first key is "fname", and it points
to the value "Donald", while the second is "lname" and it points to
"Duck".
You can also write the statement above like this:
%myhero = ("fname", "Donald", "lname", "Duck");
Accessing the elements of a hash is equally simple - in the
example above, the notation
$myhero{"fname"}
will return the first value of the hash ("Donald"), while
$myhero{"lname"}
will return the second value ("Duck").
The rules
following hash names are the same as those for scalar and array variables - a
hash name begins with a % symbol, followed by an alphabetic character, which may
be followed by one or more numbers or letters. Hashes also have their own
"space" in Perl.so the variables $duck, @duck and %duck are not treated as one
and the same.
This article copyright Melonfire
2000. All rights reserved.{mospagebreak title=Heroes Of The Silver
Screen} Here's a simple program that demonstrates how hashes can be used:
#!/usr/bin/perl
# define a hash
%director = ("1995" => "Mel Gibson", "1996" => "Anthony Minghella", "1997"
=> "James Cameron", "1998" => "Steven Spielberg", "1999" => "Sam Mendes");
# print
print "The Best Director Oscar in 1995 went to $director{1995}\n";
print "The Best Director Oscar in 1996 went to $director{1996}\n";
print "The Best Director Oscar in 1997 went to $director{1997}\n";
print "The Best Director Oscar in 1998 went to $director{1998}\n";
print "The Best Director Oscar in 1999 went to $director{1999}\n";
And here's the output:
The Best Director Oscar in 1995 went to Mel Gibson
The Best Director Oscar in 1996 went to Anthony Minghella
The Best Director Oscar in 1997 went to James Cameron
The Best Director Oscar in 1998 went to Steven Spielberg
The Best Director Oscar in 1999 went to Sam Mendes
In the example above, a hash has been used to store a bunch
of name-value pairs, and a print() function has been used to display
them.
You can also use the alternate hash notation if you prefer.
# define a hash
%director = ("1995", "Mel Gibson", "1996", "Anthony Minghella", "1997",
"James Cameron", "1998", "Steven Spielberg", "1999", "Sam Mendes");
This article copyright Melonfire
2000. All rights reserved.
