#!/usr/bin/perl --
use strict; use warnings; use Data::Dump;
use BerkeleyDB;

for my $opts ( [], [-Flags  => DB_CREATE| DB_INIT_CDB | DB_INIT_MPOOL]
+ ){
    my $env = BerkeleyDB::Env->new(
        -Home => './home',
        @$opts,
    ) or warn "cannot open environment: $BerkeleyDB::Error\n";
    dd $env, [ glob './home/*' ];
}
__END__
[download]

On first run it doesn't exist, so first try, without flags, fails -- you need flags to initialize

$ perl berkeleydb.env.pl
cannot open environment: No such file or directory
(undef, [])
(
  bless([12346044], "BerkeleyDB::Env"),
  [
    "./home/__db.001",
    "./home/__db.002",
    "./home/__db.003",
    "./home/__db.004",
  ],
)
[download]

On second run both tries work, because its already initialized

$ perl berkeleydb.env.pl
(
  bless([10087228], "BerkeleyDB::Env"),
  [
    "./home/__db.001",
    "./home/__db.002",
    "./home/__db.003",
    "./home/__db.004",
  ],
)
(
  bless([12336228], "BerkeleyDB::Env"),
  [
    "./home/__db.001",
    "./home/__db.002",
    "./home/__db.003",
    "./home/__db.004",
  ],
)
[download]