replace both upperCase and lowerCase

Code:

---

code

$myVar = 'abcdABCD';

$myVar=str_replace('a','', $myVar);

echo $myVar;

result

bcdABCD

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The code above replace 'a'.
I like to replace both "a" and "A" at a time.

Use str_ireplace() — The case-insensitive version of str_replace().
http://php.net/manual/en/function.str-ireplace.php

Code PHP:

---

$myVar = 'abcdABCD';
$myVar=str_ireplace('a','', $myVar);
echo $myVar;
result
bcdBCD

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You can use:

$myVar=str_replace('a','', $myVar);
$myVar=str_replace('A','', $myVar);

This will replace both a and A