You can print "Content-type: text/html\n\n"; first and then do your file printing and html outputting. That should work.
Perhaps something is trying to write to STDERR before you do the show_html which causes the premature... error

In reply to Re: Premature end of script headers (i know, i know...) by Jaap
in thread Premature end of script headers (i know, i know...) by andyram27

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