I can't use a db to do this

Yes of course you can!

Perl has this wonderful built-in database system, called ... hashes.

And you can persist the datastore by binding your hash to a file with dbmopen.

use strict;
use warnings;
use 5.012;

# Add some data to the datastore
my %failed_jobs;
dbmopen %failed_jobs, './failed_jobs', 0666;
$failed_jobs{'job_1234'} = 1;
dbmclose %failed_jobs;

# Now see if the data persisted
my %check_failures;
dbmopen %check_failures, './failed_jobs', 0666;
for my $job (keys %check_failures) {
    say "$job = $check_failures{$job}";
}
dbmclose %failed_jobs;
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The beauty of this is that it is totally transparent. Once you bind the hash to the database with dbmopen you keep using the hash as usual but Perl takes care of storing and fetching the data to/from storage.

For a more sophisticated version of this mechanism, check out the tie function.