Here’s a quick hack:
<?php
function regex_range($from, $to) {
if($from < 0 || $to < 0) {
throw new Exception("Negative values not supported");
}
if($from > $to) {
throw new Exception("Invalid range $from..$to, from > to");
}
$ranges = array($from);
$increment = 1;
$next = $from;
$higher = true;
while(true) {
$next += $increment;
if($next + $increment > $to) {
if($next <= $to) {
$ranges[] = $next;
}
$increment /= 10;
$higher = false;
}
else if($next % ($increment*10) === 0) {
$ranges[] = $next;
$increment = $higher ? $increment*10 : $increment/10;
}
if(!$higher && $increment < 10) {
break;
}
}
$ranges[] = $to + 1;
$regex = '/^(?:';
for($i = 0; $i < sizeof($ranges) - 1; $i++) {
$str_from = (string)($ranges[$i]);
$str_to = (string)($ranges[$i + 1] - 1);
for($j = 0; $j < strlen($str_from); $j++) {
if($str_from[$j] == $str_to[$j]) {
$regex .= $str_from[$j];
}
else {
$regex .= "[" . $str_from[$j] . "-" . $str_to[$j] . "]";
}
}
$regex .= "|";
}
return substr($regex, 0, strlen($regex)-1) . ')$/';
}
function test($from, $to) {
try {
printf("%-10s %s\n", $from . '-' . $to, regex_range($from, $to));
} catch (Exception $e) {
echo $e->getMessage() . "\n";
}
}
test(2, 8);
test(5, 35);
test(5, 100);
test(12, 1234);
test(123, 123);
test(256, 321);
test(256, 257);
test(180, 195);
test(2,1);
test(-2,4);
?>
which produces:
2-8 /^(?:[2-7]|8)$/
5-35 /^(?:[5-9]|[1-2][0-9]|3[0-5])$/
5-100 /^(?:[5-9]|[1-9][0-9]|100)$/
12-1234 /^(?:1[2-9]|[2-9][0-9]|[1-9][0-9][0-9]|1[0-2][0-3][0-4])$/
123-123 /^(?:123)$/
256-321 /^(?:25[6-9]|2[6-9][0-9]|3[0-2][0-1])$/
256-257 /^(?:256|257)$/
180-195 /^(?:18[0-9]|19[0-5])$/
Invalid range 2..1, from > to
Negative values not supported
Not properly tested, use at your own risk!
And yes, the generated regex could be written more compact in many cases, but I leave that as an exercise for the reader 🙂