Regular expressions: how to match numbers?

Question

I want to use regular expressions to match numbers like these:

58158
60360
98198

That is in the format ABCAB .

I use code below to match ABAB :

(([\d]){1,}([\d]){1,})\1{1,}

such as 5858 but how to match ABCAB(58158)?

Answer 1

For numbers in the format ABCAB :

(\d)(\d)\d\1\2

This places no restriction on A=B=C . Use negative look-ahead for A!=B!=C :

(\d)(?!\1)(\d)(?!\1|\2)\d\1\2

Edit:

There is no boundary matching so 58158 will be matched in 36958158 :

$num=36958158;
preg_match('/(\d)(?!\1)(\d)(?!\1|\2)\d\1\2/',$num,$match);
echo ">>> ".$match[0];

>>> 58158

Answer 2

To match integers in the form ABCAB, use \\b(\\d\\d)\\d(\\1)\\b .

\\b is a word boundary and \\1 references the first group.

Example (in JavaScript so that it can be tested in the browser but it works in most regex solutions) :

var matches = '58158 22223 60360 98198 12345'.match(/\b(\d\d)\d(\1)\b/g);

gives

["58158", "60360", "98198"]