You can replace all instance in a string using str_replace with the help of str_replace function. In this example, str_replace replaces all instances of abc with xyz like this:

echo str_replace("abc","xyz","abcdefghijklmn");

the output will become : xyzdefghijklmn

Str_replace will also be used with arrays.

$fruitarr=array("apple","banana","orange");

$fruit2arr=array("Apple","Banana","Orange");
echo str_replace($a,$b,"apple,banana and orange are fruits);

The out put will become : Apple,Banana and Orange are fruits. We can also use substr_replace function which replace part of the string with another string.

echo substr_replace("Apple","Banana",0); // 0 will start replacing at the first character in the string