I rearranged things a little... 
#!/usr/bin/perl

use strict;
use warnings;
use DB_File;

my $a = new DB_File::HASHINFO; 
my $doi = '10.1353/ham.2005.0020';

tie my %H, "DB_File", "audit.db", O_RDWR|O_CREAT, 0666, $a;
print "|$doi| does ", (exists $H{$doi} ? "exist!\n" : "not exist!\n");

while(my $k = each %H) { 
    if ($k eq $doi) { 
        print "|$k| eq |$doi|\n"; 
        last; # spare me the other millions... 
    } 
} 
untie %H;

[download]

In reply to Re: with tied hash, 'each' gives key that doesn't 'exists' by Khen1950fx
in thread with tied hash, 'each' gives key that doesn't 'exists' by hbm

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