The other hidden problem in your code is the construct:

open CONFIG, "$hol_file" || die "Cannot open log for writing. $!";
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This will fail silently, because of operator precedence. Use "or" instead of "||".

Best practices say you should use the 3-parameter form of "open", and local file handles, so your code should read:

open (my $config , "<", "$hol_file") or die "Cannot open '$hol_file': 
+$!";
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