Like IlyaM says, reread the docs. The examples at the ref link should explain the difference pretty much. In addition to the built in types, the functions also work for objects blessed into packages. Consider this example:

#!/usr/bin/perl -w

use strict;

# Our base, or super class
package Foo;

sub new
{
    bless {}, shift;
}

# The subclass Bar inherits from Foo
package Bar;
use base 'Foo';

# The main package
package main;

# Instantiate an object of type Bar:
my $obj = Bar->new();

# Three different kinds of tests, to see what type the object is:

print "Using ref to test which object type:\n";
print "\$obj is Bar\n" if(ref $obj eq 'Bar');
print "\$obj is Foo\n" if(ref $obj eq 'Foo');

print "Using UNIVERSAL::isa:\n";
print "\$obj is Bar or subclass of Bar\n" if(UNIVERSAL::isa($obj,'Bar'
+));
print "\$obj is Foo or subclass of Foo\n" if(UNIVERSAL::isa($obj,'Foo'
+));

print "Using object method isa:\n";
print "\$obj is Bar or subclass of Bar\n" if($obj->isa('Bar'));
print "\$obj is Foo or subclass of Foo\n" if($obj->isa('Foo'));
[download]

As you see, ref will help you find out if an object is of type X, while isa will tell you if the object is of type X, or if the package inherits from X.

Hope that helps.

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