Can you help with one regular expression?

Question

PHP

You need to find 2 spaces in a row and replace them with \t
But, you need to replace only those spaces that go before the beginning of any other characters.
For example, the string:
(4-spaces here)Text(4-spaces here too)
Should be replaced with this:
\t\tText(4-spaces here)
If you use
$str = preg_replace('/^ {2}/m', "\t", $str);
That, you get "\t(4-spaces here)Text(4-spaces here) -space)"
Any ideas?
-----------
UPD:
I don't think it's really possible to implement this just using RT.
So the question is removed. Thanks to all!

Answer 1

So? jsfiddle.net/djkyt0c6/1

Answer 2

You can add your own logic to the regular expression in PHP.

function replaceSpacesWithTabs($line, $perTab = 2)
{
    return preg_replace_callback('/^[ ]+/', 
        function ($matches) use ($perTab) {
            $len = strlen($matches[0]);
            $out = str_repeat("\t", floor($len / $perTab));
            if (($rem = $len % $perTab) > 0) {
                $out .= str_repeat(' ', $rem);
            }        
            return $out;
        },
        $line
    ); 
}

You can poke here .
On the solution of a purely regular, in my opinion, does not pull. But you can apply it for yourself.

Answer 3

$str = preg_replace('/\A[ ]{2}/m', "\t", $str);

Answer 4

was too lazy, left it like that

$str = preg_replace('/\n {4}/',"\n\t", $str);
$str = preg_replace('/\n {4}/',"\n\t", $str);
$str = preg_replace('/\n {4}/',"\n\t", $str);
$str = preg_replace('/\n {4}/',"\n\t", $str);

Answer 5

Is it important for you to do this on a regular basis? The task is elementarily solved by character-by-character scanning of the string with replacement by condition.