#!/usr/bin/perl -w
use strict;

my(@fields) = qw/field1 field2 .../ ; # all 21 of your fields CAREFULL
+Y checked

open(FH, "<control.txt") or die "yada... $!";
my($rec) ;
while (<FH>) {
    
   @$rec{@fields} = split /:/ ; # hash slice into an auto-vivified has
+h-reference (instant record)

   $recs{"$rec->{field13}$rec->{field21}"} = $rec ;
}

##
## Individual records can be manipulated by field name
##

$rec{keyOfInterest}->{fieldOfInterest} = NewValue ;

##
## to convert a rec back into a string:
##
my($str) = join ":", @$rec{@fields} ;
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I think this is doable with dbm, even if the keys are from 2 different parts of the record. I wrote an address book application that uses about 19 fields delimited to a dbm tied hash. Actually, it turned out to be a hash of arrays. Without the camel book chapter on Data Structures, I would have been lost, but they have good examples and diagrams to follow.

I am including the subroutines here without the main program. The main section is specific to the application, whereas the subroutines are more generally usable to flatten out the hash-of-array structure into the key-value pairs needed for dbm output. I use ">" for the delimiter.

use strict;
use CGI qw(:standard :html3 escape unescape);
use Apache::Constants qw(:common);
use Apache::File ();
use Apache::Util qw(ht_time escape_uri unescape_uri escape_html);
use Fcntl qw( :DEFAULT :flock );
use POSIX qw(strftime);
use DB_File;
use vars qw(@FIELDS %REQUIRED $GUESTBOOKFILE %HoA);
local *DBM;

@FIELDS = qw(First_Name Last_Name
             Email_Address1 Email_Address2 Website
             Home_Phone Work_Phone Cell_Phone Other_Phone
             Street_Address1 Street_Address2 City State Zip
             Country Birthday Gender);

sub write_guestbook {
    unless (TieLock($GUESTBOOKFILE, 1)) {
    print strong('Sorry, an error occurred: unable to open ' . $GUESTB
+OOKFILE),p();
    return;
        }

    my $i = param("HoAindex"); # check for an update
    unless ($i) {
      ## increment the sequencer.
      $HoA{sequence} = 0 unless exists $HoA{sequence};
      $i = ++$HoA{sequence};
      }

    my $date = strftime('%d-%b-%Y %R',localtime);
    $HoA{$i} = join(">", ($date), map {escape(param($_))} (@FIELDS));

    unTieLock($GUESTBOOKFILE);
    return( "Thank you <b>". param('First_Name')
                     ."</b>, for signing the guestbook.");
}

sub delete_guestbook {
    unless (TieLock($GUESTBOOKFILE, 1)) {
    print strong('Sorry, an error occurred: unable to open ' . $GUESTB
+OOKFILE),p();
    return;
        }

    my $i = param("HoAindex"); # get the delete index
    unless ($i) {
    print strong('Sorry, an error occurred: unable to get entry index 
+' . $GUESTBOOKFILE),p();
    return;
      }

    delete $HoA{$i};

    unTieLock($GUESTBOOKFILE);
    return( "Thank you <b>". param('First_Name')
                     ."</b>, your delete has been completed.");
}

sub load_address {
    my $fname = param('First_Name');
    my $lname = param('Last_Name');
    my $return_msg;

    unless (TieLock($GUESTBOOKFILE, 0)) {
    print strong('Sorry, an error occurred: unable to open ' . $GUESTB
+OOKFILE),p();
    return;
        }

    my @data;
    for my $addr (sort keys %HoA) {
    @data =  map {unescape($_)} split( ">", $HoA{$addr}, 18);
        $data[0] = $addr;              #overlay the date with the key.
        last if ($fname eq $data[1]) && ($lname eq $data[2]);
        if ($data[0] eq "sequence") {
          @data = ();
          $return_msg = "Sorry <b>". param('First_Name')
                     ."</b>, but your existing entry has not been foun
+d.";
          }
        }

    unTieLock($GUESTBOOKFILE);
    return ($return_msg, @data);
}

sub view_guestbook {
    my $guestbook;

    my @rows;
    unless (TieLock($GUESTBOOKFILE, 0)) {
    print strong('Sorry, an error occurred: unable to open ' . $GUESTB
+OOKFILE),p();
    return;
        }

    for my $addr (sort keys %HoA) {
        next if $addr eq "sequence";
    my @data =  map {unescape($_)."&nbsp;"} split( ">", $HoA{$addr}, 1
+8);
    unshift @rows, td(\@data);
        }

    unshift @rows, th(['Entry Date',@FIELDS]);
    $guestbook .= p(
        table({-border=>'1', -hspace=>'5',
                   -cellspacing=>'1', -cellpadding=>'4'},
          TR(\@rows)));

    unTieLock($GUESTBOOKFILE);
    return ($guestbook);
}

sub TieLock { # tie and lock the dbm file.
   my $path = shift;
   my $for_writing = shift;
   my $lock_type;
    if ($for_writing) {
    $lock_type = LOCK_EX; 
    } 
    else {
    $lock_type = LOCK_SH; 
    }
   my $db = tie %HoA, 'DB_File', $path, O_RDWR | O_CREAT, 0666, $DB_HA
+SH
       or die "[Error processing $path ] $!";

   my $fd = $db->fd;
   open DBM, "+<&=$fd" or die "Could not dup DBM for lock: $!";

# now try to lock it
   my $success;
   my $tries = 0;
   while ($tries++ < 10) {
    last if $success = flock (DBM, $lock_type|LOCK_NB);
    print p("Waiting for $lock_type lock on AddressBook file...");
    sleep(1);        # wait a second
        }

   undef $db;
   unless ($success) {
    warn("Couldn't get lock for $lock_type"); 
    return;
        }
   return 1;
   }

sub unTieLock { # untie the dbm file.
   untie %HoA;
   close DBM;
   }
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