sprintf("%-$line_width" . "s", $line) . $line_delimiter;

I think all the concatenation in this line is a little confusing. I'd prefer to interpolate everything in the format string. My assumption is that you are using the sprintf as the return from a subroutine or a do block. Obviously, use printf if you expect actual output.

sprintf qq{%-${line_width}s$line_delimiter}, $line;
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I hope this is of interest.