use strict;
use warnings;
use Math::Algebra::Symbols;

my $file = <<FILE;
e = a & b;
f = e | c;
d = ~f;
FILE

open my $fIn, '<', \$file or die "Can't open file: $!\n";

my %subst;
my $last;

while (<$fIn>) {
    chomp;
    s/;$//;

    my ($lhs, $rhs) = split /\s*=\s*/, $_, 2;

    $rhs =~ s/(\w+)/exists $subst{$1} ? "($subst{$1})" : $1/ge;
    $subst{$lhs} = $rhs;
    $last = "$lhs = $rhs";
}

print $last;

##</code><code>##

d = ~((a & b) | c)