A demonstration of how to convert a Berkeley DB file. Discussion here: libdb.wordpress.com

bdb_convert_file

#!/usr/bin/perl
#
# Copyright (c) 2011
#	Donald D. Anderson.  All rights reserved.
#
# Redistribution and use in source and binary forms are permitted.
# This software is provided 'as is' and any express or
# implied warranties, including, but not limited to, the implied
# warranties of merchantability, fitness for a particular purpose, or
# non-infringement, are disclaimed.
#
################################################################
#
# Usage:  bdb_convert_data fromfile tofile
# 
# Converts data in a Berkeley DB database.
# Can be customized to remove or add bytes to each record,
# and even add new records.
#
# Warning: this should normally be used on a quiet system (or best, a
# system that has no live BDB processes.  There is nothing
# transactional about this script!
#
# Warning: should not be used if you've changed your btree compare function
# (since db_load will not do the right thing).
#
# See discussion on http://libdb.wordpress.com

die "Usage: $0 fromfile tofile" if ($#ARGV != 1);
$from = $ARGV[0];
$to = $ARGV[1];
die "$0: $from: does not exist" if (! -f $from);
die "$0: $to: exists, will not overwrite" if (-f $to);
open IN, "db_dump $from|" || die "$0: cannot run db_dump";
unlink "$to.TMP";
open OUT, "|db_load $to.TMP" || die "$0: cannot run db_load";

# convert_key and convert_value are called with $_ set to
# a data line from the db_dump output.  Each data line starts
# with a single space, then there are hex digits, a pair of hex
# digits for each 8 bit char.  E.g. ' 65696e7320d0bfd1' is 8 bytes.

# This convert_key passes through the key without modification
sub convert_key() {
    $line=$_;
    #print "key: $line";
    print OUT "$line";
}

# This convert_value 'removes' the second 4 bytes, for demonstration
# !! **** modify this as necessary **** !!
#
sub convert_value() {
    $line=$_;

    # !! **** here's the custom part **** !!
    if (length($_) > 17) {
      $line = substr($_,0,9) . substr($_,17);
    }

    #print "dat: $line";
    print OUT "$line";
}

$iskey = 1;

# The dbdump format contains some header info, that starts
# in the first column.  Those lines are copied directly.
# The data appears with a single space in the first column,
# followed by a bunch of hex numbers.  Lines of data alternate
# between keys and values.
while (<IN>) {
    if (/^ /) {
        if ($iskey) {
            &convert_key;
        } else {
            &convert_value;
        }
        # alternate lines
        $iskey = ! $iskey;
    }
    else {
        print OUT $_;
    }
}
close (IN);
close (OUT);
rename "$to.TMP", "$to";