I'd do:

sub hash_join (\%$$) {
  my ($h, $between, $end) = @_;
  my $str;

  while (my($k,$v) = each %$h) {
    $str .= "$k$between$v$end";
  }

  return $str;
}

print hash_join %ENV, "=", "\n";
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japhy -- Perl and Regex Hacker