How to write simple form validation in PHP

With the development of the Internet, form validation has become a necessary element for any website. As a popular back-end language, PHP also provides rich form validation functions. In this article, we will learn how to write simple form validation in PHP.

Why form verification is needed

Form verification is an important measure to ensure data security. By validating the data entered by users, we can prevent some common security issues, such as SQL injection, cross-site scripting attacks (XSS), etc.

In addition, form validation can also ensure the accuracy and completeness of data. At the application level, accuracy and completeness prevent confusion among users and make data more reliable. Without form validation, users can easily change data without authorization, compromising the integrity of the system.

How to perform form validation

PHP provides a variety of functions to verify input data, including: is_numeric(), is_string(), ctype_digit(), etc. PHP also supports regular expressions, which are an efficient way to validate character patterns.

Below we will demonstrate a few examples of form validation using PHP built-in functions and regular expressions:

1. Validate email address

Email Address is a common form field. PHP built-in function filter_var() can easily verify email addresses. Here is a simple example:

$email = "john.doe@example.com";
if(filter_var($email, FILTER_VALIDATE_EMAIL)){
echo "Valid email address!" ;
}else{
echo "Invalid email address!";
}

In the above example, the filter_var() function uses the FILTER_VALIDATE_EMAIL filter to verify that the entered email address is legitimate. If the email address is valid, "Valid email address!" is output, otherwise "Invalid email address!" is output.

2. Validate Date

Date is another common form field. The PHP built-in function strtotime() can convert most strings to datetime. The following is an example of validating a date:

$date = "2021-03-23";
if(date('Y-m-d', strtotime($date)) === $date) {
echo "Valid date!";
}else{
echo "Invalid date!";
}

In the above example, the strtotime() function converts the string Convert $date to a datetime, then use the date() function to format the date as YYYY-MM-DD. If the date is still $date after formatting, it means the date format is legal.

3. Verify password

Password verification usually needs to be performed when the user enters the password. The following is an example of verifying password strength:

$password = "Abc1234";
if (preg_match("/^.(?=.{8,})(?=.d)(?=.[a-z])(?=.[A-Z]).*$/", $password)){
echo "Valid password!";
}else{
echo "Invalid password!";
}

In the above example, regular expressions are used to verify password strength. Regular expression^.(?=.{8,})(?=.d)(?=.[a-z])(?=.[A-Z]).* $ indicates that the password must meet the following conditions: be at least 8 characters long, contain at least one number, at least one lowercase letter, and at least one uppercase letter.

Conclusion

Form verification is an important measure to ensure data security. PHP built-in functions and regular expressions provide a variety of verification methods. This article presents several examples of writing simple form validation in PHP. Of course, form validation is not foolproof, and attackers may use various means to bypass form validation. Therefore, we also need other security-level measures, such as careful script execution, encryption, and prevention of cross-site scripting attacks.

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