G'day PilotinControl,

As your files are very small, you could just make working copies where usage is flagged. Each time you find the temp file has been deleted, just recreate the working copies from the master files.

Here's a proof-of-concept script.

#!/usr/bin/env perl

use strict;
use warnings;
use autodie;

use File::Copy;
use Tie::File;

my $master_ext = '.master';
my $used_ext = '.used';
my $year_file_base = 'pm_year_make_model_file_years';
my $make_file_base = 'pm_year_make_model_file_makes';
my $model_file_base = 'pm_year_make_model_file_models';
my $temp_file = 'pm_year_make_model_temp_file';

my $used_years = "$year_file_base$used_ext";
my $used_makes = "$make_file_base$used_ext";
my $used_models = "$model_file_base$used_ext";

if (! -e $temp_file) {
    copy("$year_file_base$master_ext", $used_years);
    copy("$make_file_base$master_ext", $used_makes);
    copy("$model_file_base$master_ext", $used_models);
}

tie my @years, 'Tie::File', $used_years;
tie my @makes, 'Tie::File', $used_makes;
tie my @models, 'Tie::File', $used_models;

my $year = select_item('year', \@years);
my $make = select_item('make', \@makes);
my $model = select_item('model', \@models);

untie @years;
untie @makes;
untie @models;

open my $fh, '>>', $temp_file;
print $fh "$year $make $model\n";
close $fh;

print "Temp file contents:\n";
system cat => $temp_file;

sub select_item {
    my ($item, $records_ref) = @_;
    my %item_index_for =
        map { $records_ref->[$_] => $_ }
        grep { $records_ref->[$_] !~ /^#/ } 0 .. $#$records_ref;

    print "Available ${item}s:\n";
    print "$_\n" for sort keys %item_index_for;
    print "Select $item: ";
    chomp(my $selection = <STDIN>);
    substr($records_ref->[$item_index_for{$selection}], 0, 0) = '#';
    return $selection;
}
[download]

Here's some sample runs:

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