use strict;
use warnings;

my %hash = (a => 1, b => 0, c => 3);

while (<DATA>){
    chomp;
    s/(\w+)/\$hash{$1}/g;
    
    my $ans = eval "$_";
    
    if ($@) {
        print "Eval of $_ failed:\n   $@\n";
    } else {
        print "$_ = $ans\n";
    }
}

__DATA__
a/b
b+c
c*a/(b+a)

##</code><code>##

Eval of $hash{a}/$hash{b} failed:
   Illegal division by zero at (eval 10)[noname.pl:10] line 1, <DATA> line 1.

$hash{b}+$hash{c} = 3
$hash{c}*$hash{a}/($hash{b}+$hash{a}) = 3