#!/usr/bin/perl
use warnings;
use strict;

my $part_2 = "Not a good idea";
my $var1 = "part";
my $var2 = "2";
my $compound = eval "\$${var1}_$var2";

print "$compound\n";

__END__

There are three important things to note about this:
1. it is a really bad idea
2. the first $ must be escaped to avoid the first evaluation (the
interpolation into the string)
3. $var1 must be in the form of ${var1} because $var1_ is a valid variable name