如何使用PHP的正则表达式获得所有这种模式的出现？

Question

How can I get, into an array, all occurrences of this pattern 4321[5-9][7-9]{6} but excluding, for example, the occurrences where there is a digit immediately before the value, or immediately after it?

For instance, 43217999999 should be valid but 1 43217999999 (note the number 1 at the beginning) should not be valid.

As the first example, 43217999999 1 shouldn't be valid because of the 1 that it has in the end.

The added difficulty, at least for me, is that I have to parse this in whatever position I can find it inside a string.

The string looks like this, literally:

43217999997 / 5 43217999999 // 43217999998 _ 43217999999a43216999999-43216999999 arandomword 43215999999 7

As you would be able to note, it has no standard way of separating the values (I marked in bold the values that would make it invalid, so I shouldn't match those)

My idea right now is something like this:

(\D+|^)(4321[5-9][7-9]{6})(\D+|$)

(\\D+|^) meaning that I expect in that position the start of the string or at least one non-digit and (\\D+|$) meaning that I expect there the end of the string or at least one non-digit.

That obviously doesn't do what I picture in my head.

I also tried do it in two steps, first:

preg_match_all("/\D+4321[5-9][7-9]{6}\D+|4321[5-9][7-9]{6}\D+|4321[5-9][7-9]{6}$/", $input, $outputArray);

and then:

for($cont = 0; $cont < count($outputArray); $cont++) {
   preg_match("/4321[5-9][7-9]{6}/", $outputArray[0][$cont], $outputArray2[]);
}

so I can print

echo "<pre>" . print_r($outputArray2, true) . "</pre>";

but that doesn't let me exclude the ones that have a number before the start of the value ( 5 432157999999 for example), and then, I am not making any progress with my idea.

Thanks in advance for any help.

Answer 1

If you literally want to check if there is no digit before or after the match you can use negative look ahead and look behind.

• (?![0-9]) at the end means: "is not followed by 0-9"
• (?<![0-9]) at the start means: "is not preceded by 0-9"

See this example https://regex101.com/r/6xbmJk/1