Php用2个其他随机字符替换2个字符

Question

I want to swap 2 characters in a string with 2 other ones.

Start string = "`bHello `!how `Qare `%you."

Random string = "1234567890abcdefghijklmnopqrstuvwxyz!£$%^&@"

How do i swap `b `! `Q `% with random ones so it looks something like this

End result string = "`4Hello `^how `$are `@you."

I have tried this so far

I tried so far

$out = "`vHow `!are `@you."

$patterns = array("`1","`J","`2","`3","`4","`5","`6","`7","`!","`$","`%","`^","`&","`)","`~","`#","`@","`q","`e","`y","`t","`p","`j","`k","`l","`M","`x","`v","`m","`Q","`E","`R","`T","`Y","`P","`G","`K","`L","`X","`V");

$pretest = array("`1","`J","`2","`3","`4","`5","`6","`7","`!","`$","`%","`^","`&","`)","`~","`#","`@","`q","`e","`y","`t","`p","`j","`k","`l","`M","`x","`v","`m","`Q","`E","`R","`T","`Y","`P","`G","`K","`L","`X","`V");

$tempstr = $pretest[rand(0, strlen($pretest)-1)];

$substs = "`".$tempstr;

$out = preg_replace($patterns, $substs, $out);

However the end result is

$out = "`%How `%are `%you."

it picks only 1 random and changes them all to that one.

Answer 1

<?php
function randomChar() { 
    $rand = "1234567890abcdefghijklmnopqrstuvwxyz";
    return substr($rand, rand(0, strlen($rand)), 1);  
} 

echo preg_replace_callback("/`./", 'randomChar', "`bHello `!how `Qare `%you.");