$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;

##</code><code>##

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

##</code><code>##

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