Adding, Changing, and Removing Elements - Perl

Hash entries are very much like ordinary scalar variables, except that you need not declare an individual hash key before assigning to it or using it. We can add a new person to our hash just by assigning to their hash entry:

$where{Eva} = "Uxbridge";
print "Eva lives in $where{Eva}\n";

A new entry springs into existence, without any problems. We can also change the entries in a hash just by reassigning to them. Let’s move people around a little:

$where{Eva}      = "Denver";
$where{Samantha} = "California";
$where{Lucy}     = "Tokyo";
$where{Gary}     = "Las Vegas";
$where{Ian}      = "Southampton";

print "Gary lives in $where{Gary}\n";

To remove an entry from a hash, you need to use thedelete()function, as we do in this little variant onhash.pl:

#!/usr/bin/perl -w
# badhash.pl

use strict;

my %where = (
        Gary     => "Dallas",
        Lucy     => "Exeter",
        Ian      => "Reading",
        Samantha => "Oregon"
);

delete $where{Lucy};
print "Lucy lives in $where{Lucy}\n";

You can see that here we delete Lucy’s entry in
%wherebefore we access it, so executing this program should produce an error. Sure enough, we get

$ perl badhash.pl
Use of uninitialized value in concatenation (.) at badhash.pl line 14
Lucy lives in
$

It’s not that we haven’t initialized poor Lucy, but rather that we’ve decided to get rid of her.

Please check back for the conclusion to this article.