and if I was more careful about analyzing error output I would have seen that. Damn tye, you rock.

So fd_retrieve doesn't work on an empty file, it only works on storable data. I would think it should return an empty hashref - but hey, it doesn't and I can deal with that now that I know it.

The working revised code:

#!/usr/bin/perl -w
# start with no existing giant.db file
use strict;
use Fcntl qw(:DEFAULT :flock);
use Storable qw(store_fd fd_retrieve retrieve);
use Data::Dumper;
$Data::Dumper::Deepcopy=1;
$Data::Dumper::Purity=1;
$Data::Dumper::Sortkeys=1;

my %data = ( 1 => 'FEE', 2 => 'FYE',
             3 => 'FOH', 4 => 'FUM', );

my $exists = (-e "giant.db"?1:0);
sysopen(*DB, "giant.db", O_RDWR|O_CREAT, 0666) or die("sysopen: $!\n")
+;
flock(*DB, LOCK_EX) or die("flock: $!\n");
my $hashref = $exists?fd_retrieve(*DB):{};

# modify the data, do work, etc..
$hashref->{$_} = $data{$_} for sort keys %data;

store_fd($hashref, *DB) or die("store_fd: $!\n");
truncate(*DB, tell(*DB));
close(*DB);
[download]

and you can check the resultant giant.db file on the command line with:

perl -MStorable -MData::Dumper -e '{print Dumper(retrieve("giant.db"))
+}'
[download]

Thanks!