I assume you meant "I know that I can get the value for a certain key if it is the only value for that key".

There are two methods to store more than one value per key: The simple one using string concatenation of the different values and a more sophisticated one where you store a link to an array as hash value. Here is how to do it with string concatenation:

$hash{$key}= 'ape:b:cat' #stores the values 'ape','b' and 'cat' into t
+he hash using ':' as delimiter
#simple but the delimiter better not be in any values (you would have 
+to escape the delimiter which is messy)

@values= split /:/,$hash{$key}; #get the values out of the string
# checking for a specific value 
if ($hash{$key}=~/(^|:)$whatimlookingfor(:|$)/) {
  print "found it"; 
}

$hash{$key}.= ':' . $anothervalue; #add another value (but if the hash
+ value was empty you have just added two values, an empty string and 
+$anothervalue. This is another disadvantage)
[download]

The other method uses arrays to store the values. The structure is commonly called HashofArrays (HoA). The syntax is a bit more complicated, but it avoids some disadvantages of the first method

$hash{$key}= ['ape','b','cat']; #stores the values 'ape','b' and 'cat'
+ into the hash

@values= @{$hash{$key}}; #get all the values
$value= $hash{$key}->[2]; #get the third value
$value= $hash{$key}[2]; #get the third value, short form

push @{$hash{$key}}, $anothervalue; #add a value
[download]

As you can see the second method should be prefered, but if the syntax of a HashofArrays looks daunting to you or you have other compelling reasons, the first method can be used as well