#!/usr/bin/perl

use strict;
use warnings;

my %vars;
my %depend;

while (<DATA>) {
  chomp;
  if (/^\s*(\w+)\s*=\s*(?:"([^"]*)"|(.*))/) {
    my ($name, $val) = ($1, $+);
    $vars{$name} = $val;
    $depend{$name} = [ $vars{$name} =~ /\$(\w+)/g ];
  }
}

expand(\%vars, \%depend);

sub expand {
  my ($varhash, $dephash, $queue) = @_;

  $queue ||= [ keys %$varhash ];

  # for each item in the queue
  for (@$queue) {

    # make sure its dependencies are expanded
    expand($varhash, $dephash, $dephash->{$_});

    # then interpolate the variables in this item
    $varhash->{$_} =~ s/\$(\w+)/$varhash->{$1}/g;
  }
}

use Data::Dumper;
print Dumper(\%vars);

__DATA__
VAR1 = "say $VAR2"
VAR2 = "hi $VAR3"
VAR3 = jeff