Attempting include incfile1.txt
This is incfile1.txt

Attempting include incfile2.txt
This is incfile2.txt

Attempting include incfile3.txt
This is incfile3.txt

<?php
for($x = 1; $x <= 3; $x++) {
    $incfile = "incfile$x".".txt";
    print "Attempting include $incfile<br />";
    include("$incfile");
    print "<br /><br />";
}
?>
incfile1.txt
incfile2.txt
incfile3.txt