sub mysub {
	print STDERR "This is printed before the error message.\n";
	return "\nThis is printed in the middle of the error message.";

}
open(TMPFILE,"<datafile.txt") || die  "Cant open: $!" .  mysub();



##</code><code>##

This is printed before the error message.
Cant open: No such file or directory
This is printed in the middle of the error message. at temp.pl line 6.