How to add a space between every sequence of four characters (like a credit card number)?

For your sample input, this task can be completed with one function call and without generating a temporary array.

$string = '56A19E6D77828'; var_export(preg_replace('~.{4}\K~', ' ', $string)); // '56A1 9E6D 7782 8' 

If you need to be careful to not add an extra trailing space when the string length is a factor of four, then just check that you haven't reached the end of string anchor.

$string = '56A19E6D77828333'; var_export(preg_replace('~.{4}\K(?!$)~', ' ', $string)); // '56A1 9E6D 7782 8333' 

Demo Link

The pattern is simple:

1. match any four characters (.{4})
2. forget the match characters but retain the position (\K)
3. check that the end of the string hasn't been met ((?!$)
4. add the space to the position in the string

No string explosions or array implosions, just direct string manipulation.

If anyone needs to split different numbers for each split and then join them together, It's super hacky but this works, had to split a gift card that gets rendered.

$card = "603628385592165882327"; $test = str_split($card, 6); $test1 = str_split($card, 5); $test2 = str_split($card, 6); $test3 = str_split($card, 4); $number = $test[0]; $number .= " "; $number .= $test1[1]; $number .= " "; $number .= $test2[2]; $number .= " "; $number .= $test3[3]; echo $number; 

result

603628 83855 165882 1658

Version without temporary array:

$number = '56A19E6D77828'; echo trim(chunk_split($number, 4, ' '));