用字符串中的逗号和空格替换3d空格

Question

To replace a whitespace with a comma and whitespace in a string I should do something like this:

$result = preg_replace('/[ ]+/', ', ', trim($value));

The result: Some, example, here, for, you

However, I only want to replace the 3d white space, so that the result would look like this:

Some example here, for you

How do I do that?

Answer 1

You may use something like

$value = " Some example here for you ";
$result = preg_replace('/^\S+(?:\s+\S+){2}\K\s+/', ',$0', trim($value), 1);
echo $result; // => Some example here, for you

See the PHP demo and the regex demo.

Pattern details

• ^ - start of string
• \S+ - 1+ non-whitespaces
• (?:\s+\S+){2} - two consecutive occurrences of
  • \s+ - 1+ whitespaces
  • \S+ - 1+ non-whitespaces
• \K - a match reset operator
• \s+ - (the $0 in the replacement pattern references this substring) 1+ whitespaces.