Yeah, compare the paths in the /tmp/inc.XXX files to see how they differ. If the CGI version isn't printing the file maybe try to test the file open like:

open $fh, ">", "/tmp/inc.$$" or die "error: failed to open file=/tmp/i
+nc.$$ for writing.\n";
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If you know how to check if it's the CGI version you can change the file name from /tmp/inc.$$ to /tmp/inc.cgi or /tmp/inc.cl to make it easier to know which is which. But the time stamps should help with that as is.