What are the best practices for validating strings in PHP to ensure they only contain certain characters?

When validating strings in PHP to ensure they only contain certain characters, the best practice is to use regular expressions. Regular expressions allow you to define a pattern that the string must match in order to be considered valid. By using the `preg_match` function in PHP, you can easily check if the string contains only the allowed characters. 

// Define the allowed characters using a regular expression pattern
$pattern = '/^[a-zA-Z0-9]*$/';

// Input string to validate
$input = "abc123";

// Check if the input string only contains the allowed characters
if (preg_match($pattern, $input)) {
    echo "String is valid";
} else {
    echo "String contains invalid characters";
}

Keywords

filter_var preg_match regular expressions sanitization validation

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