To convert the fractions into floating point numbers that perl can directly deal with, you need to split them up. Some ways:

$num = "6/2";
# like this
$num =~ s:^(\d+)/(\d+)\z:$1/$2:e;
# or
my ($n,$d) = split "/", $num;
$num = $n/$d;
# or (unsafe for untrusted input)
$num = eval $num;
[download]

But that isn't sufficient if you need to preserve the fractional values. Floating point will introduce some round-off error. For instance, adding 1/6 six times may not get you 1:

$ perl -we'print "not equal" if 1/6 + 1/6 + 1/6 + 1/6 + 1/6 != 1'
not equal
[download]

Math::BigRat (which I've never actually used) is a core module to handle this for you.

$ perl -we'use Math::BigRat; $onesixth = Math::BigRat->new("1/6");
> print "equal" if $onesixth+$onesixth+$onesixth+$onesixth+$onesixth+
>                  $onesixth == 1'
equal
[download]