I am trying to match a partial ISBN (the last 5 digits before the checksum) against a hashref keyed by full ISBNs.

Mostly, I'm working with complete 10-digit ISBNs but for the occasional incompletes, I'd like to be able to use an expression as the key with exists. Something like this... 
if ( $incomplete_isbn =~ m/^\d{5}$/ ) {
    my $re_key = qr/.+$incomplete_isbn.+/;

    if ( exists $hashref_isbn->{$re_key} ) {
        print "Found! $incomplete_isbn matches $hashref_isbn->{$re_key
+}\n";
        }
    }

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In reply to Possible to use an expression as the hash key with exists? by wenD

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