Your script does print Fail. But my guess is that rather than get '123456789' from the code you get it from STDIN (something like $param_value = <>;) which would mean there is a \n character at the end. You can solve this like that:

chomp($param_value);
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If that's not your issue, you'll have to show us code where the problem is actually present. See How do I post a question effectively?.

Edit: you would be able to see the extra char with either of these:

use Data::Dumper;
$Data::Dumper::Useqq = 1;
...
print Dumper $param_value;
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or

use Data::Dump "pp";
...
pp $param_value;
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I personally prefer Data::Dump, but Data::Dumper should already be installed on your machine.