Possible inputs:

{d}= digit(s)

{d}.{d}.{d}.{d} AND {d}.{d}.{d}

Now how can I validate that $x is valid?

BTW {d} could equal 23746983268345687346 or 3, but not -658

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preg_match('/^\d+\.\d+\.\d+(\d+\.)?$/', $x)

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if (preg_match("/[0-9+]/",$x) {

 if (preg_match("/^[0-9]+$/",$x) {

means any numbers between 0 and 9.
The + means there must be atleast 1 or more.
and the ^ and $ mean it must span the whole block.
(^=start, $=end)
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mnb93Author Commented:
m1tk4's way looks correct, however neester's way doesn't look correct to me, how would: /^[0-9]+$/",$x parse true this:


if (preg_match('/^\\d+$/', $number)) echo "VALID";
else echo "NOT VALID";
Awww sorry!

I read this wrong:

"BTW {d} could equal 23746983268345687346 or 3, but not -658"

This will work :)

if (preg_match("/^([0-9]|\.)+$/",$x) {
How about this:

if (preg_match("/^[\d\.]+$/", $x) {
  // $x is only digits and dots
  $digits = explode('.', $s);
  // now you can use $digits[0], [1], [2], etc to get the blocks of digits (see warning below)
} else {
  // not match

This is similar to neester's proposed solution but goes a step further to separate the digits.  Warning: Both my and neester's comments have a similar "issue" that they accept {d}..{d} with multiple period separators.  If single periods are a must and ONLY three or four blocks of digits are allowed, m1k4 was ALMOST correct.  His last grouping had the period and \d reversed.   Should be:

preg_match("/^\d+\.\d+\.\d+(\.\d+)?$/", $x);
preg_match("/^[\d\.]+$/", $x)  will also match ...3.2.

preg_match("/^\d+\.\d+\.\d+(\.\d+)?$/", $x); is a correct answer
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