What you're trying to do is not a good idea. The contents read in from '$inputfile' is text. Using that text as a reference to a variable is a way to ask for all sorts of pain.

My suggestion would be to put a plain text 'placeholder' and then do a search and replace within your script.

select * from all_tables where table_name = 'PLACEHOLDER'
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$readline =~ s/PLACEHOLDER/$table_name/;
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Because trust me - using variable names as 'plain text' is bad news for all sorts of reasons. If you're really set on going that way, you will want to look at 'references'. See: perlreftut.