Another good use for references is to avoid making 'copies' of data that is being passed to a sub in the arguments list (you simply pass addresses to given variables so that you may use those addresses -- references -- inside the sub to access original variable values). Passing references to original variables may also prove useful when you see a need in modifying the original variable inside a subroutine.
Here's a pretty basic exaple: 
sub by_val {
   my ($foo) = @_;
   print "Foo = $foo\n";
   $foo = 10;             # only 'foo' belonging to this sub is modifi
+ed
}

sub by_ref {
    my ($foo_ref) = @_;
    print "Foo = $$foo_ref\n"; # pring value in 'bar'
    $$foo_ref = 10;            # will modify 'bar'
}

my $bar = 5;

by_val($bar);
print "bar = $bar\n";
by_ref(\$bar);        # $bar may no be modified inside the sub.
print "bar = $bar\n";

[download]

I'm also a fan of using references when passing large chunks of text (string variables) around to be used in various subroutines. This again boils down to not having to copy contents of a variable.

"There is no system but GNU, and Linux is one of its kernels." -- Confession of Faith

In reply to Re: Re: Trying to learn about References by vladb
in thread Trying to learn about References by dru145

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