# get rid of env that you don't need, in case you're in another build environment
# (say it isn't using the same CC or make that perl used/uses)
cleanup_environment();

# set up environment - bypass as many make-maker prompst as possible,
$ENV{PERL_MM_USE_DEFAULT} = 1;
# add the directory we're installing to to the PERL5LIB so we can find them
# after we install 'em.
$ENV{PERL5LIB} = File::Spec->catdir($install_base, 'lib');

# I'm assuming the CPAN modules are somewhere local and already downloaded.
chdir($modules_are) or die "Can't find CPAN modules";

my %tarballs = map {
  guess_package($_) => {
    tar => $_, # keep the original tarball name
    # extract the tarball to find out where the tarball is.
    dir => File::Spec->catdir($modules_are, extract_tarball($_)),
  }
} grep {
  # remove your RCS directories/files...
  not /CVS/ and
  not /~$/ and # ...
  not is_module_installed($_) # maybe it's part of the core on this platform already.
} glob '*.tar*';

# loop through them, attempting to install each one.
while (keys %tarballs)
{
   my $count = scalar keys %tarballs;
   try_install($_) foreach keys %tarballs;
   # did we make progress?
   die "Can't meet any more pre-reqs" if $count == scalar keys %tarballs;
}
exit 0;

### functions (not all are here - left as excersise for the reader)
sub extract_tarball
{
  my $tarball = shift;
  # figure out command based on extention...
  # e.g., /tar\.gz$/ => "gunzip -c $tarball | "
  #       /tar\.Z$/  => "zcat $tarball | "
  #       /tar$/     => "cat $tarball | "
  $cmd .= 'tar xf -';

  open my $tar, "$cmd |" or die ...;
  while (<$tar>)
  {
    print;
    next if $subdir;
    $subdir = $1 if m{...}; # pull out the directory name being extracted.
  }
  $subdir
}

sub try_install
{
  my $module = shift;
  my $data   = $tarballs{$module};
  chdir $data->{dir};
  if (-e 'Build.PL')
  {
    try_install_Build($data);
  }
  elsif (-e 'Makefile.PL')
  {
    try_install_Makefile($data);
  }
  else
  {
    die ...
  }
  delete $tarballs{$module} if $data->{installed};
}