<?php

function boolStr($val) {
	return $val ? 'true' : 'false';
}

$rArr = ['4 слэша' => '~^\\\\d$~', '3 слэша' => '~^\\\d$~', '2 слэша' => '~^\\d$~'];
$sArr = ['1 слэш ' => '\d', '2 слэша' => '\\d'];

foreach($rArr as $kR => $r)
	foreach($sArr as $kS => $s)
		printf('%8s =~ %8s = %s%s', $kR, $kS, boolStr(preg_match($r, $s)), PHP_EOL);