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################
#COMPARE_N_SUBSTITUTE
#Compare a hash to a fall-through hash.  If any values are present in the fall-through and not in the current values then insert them in the DYC hash.
#compare_n_substitute(hash1, hash2)  #insert key-value-pairs from hash2 into hash1 only if those pairs are not defined in hash1.
#compare_n_substitute(%hash, %default)
sub compare_n_substitute(%%) {
my ($hashref, $fallthrough_hashref) = @_;
for my $key (keys %$fallthrough_hashref) {
unless (defined($$hashref{$key})) {
$$hashref{$key} = $$fallthrough_hashref{$key};
}
}
}

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