How can special characters be allowed in a variable while restricting it to only a-z, A-Z, and numbers in PHP?

To allow special characters in a variable while restricting it to only a-z, A-Z, and numbers in PHP, you can use a regular expression to validate the input. By using the preg_match function, you can check if the variable contains only the allowed characters. If the input contains any characters outside of a-z, A-Z, and numbers, it can be rejected. 

$variable = "abc123!"; // Variable with special character

if (preg_match('/^[a-zA-Z0-9]+$/', $variable)) {
    echo "Variable contains only a-z, A-Z, and numbers.";
} else {
    echo "Variable contains special characters and is not allowed.";
}

Keywords

Regular expressions preg_replace PHP character class alphanumeric.

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