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PHPprogramming~5 mins

Common validation patterns in PHP

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Introduction

Validation helps check if data is correct before using it. It stops mistakes and keeps programs safe.

When a user fills a form and you want to check if the email looks right.
When you want to make sure a password is strong enough.
When you need to confirm a number is within a certain range.
When you want to check if a required field is not empty.
When you want to verify a date is in the correct format.
Syntax
PHP
<?php
// Example of validating an email
if (filter_var($email, FILTER_VALIDATE_EMAIL)) {
    // valid email
} else {
    // invalid email
}
?>
Use PHP's built-in filter_var function for common validations like email and URL.
You can use regular expressions with preg_match for custom patterns.
Examples
This checks if the email is in a correct format.
PHP
<?php
// Validate email
$email = 'user@example.com';
if (filter_var($email, FILTER_VALIDATE_EMAIL)) {
    echo 'Valid email';
} else {
    echo 'Invalid email';
}
This checks if a number is between 18 and 99.
PHP
<?php
// Validate number range
$age = 25;
if ($age >= 18 && $age <= 99) {
    echo 'Age is valid';
} else {
    echo 'Age is invalid';
}
This checks if the name is not empty.
PHP
<?php
// Validate non-empty string
$name = 'John';
if (!empty($name)) {
    echo 'Name is provided';
} else {
    echo 'Name is missing';
}
This checks if the phone number matches the pattern 123-456-7890.
PHP
<?php
// Validate pattern with regex
$phone = '123-456-7890';
if (preg_match('/^\d{3}-\d{3}-\d{4}$/', $phone)) {
    echo 'Phone number is valid';
} else {
    echo 'Phone number is invalid';
}
Sample Program

This program checks if the email is correct, password is at least 8 characters, and age is between 18 and 99.

PHP
<?php
// Sample program to validate user input
$email = 'test@example.com';
$password = 'Pass1234';
$age = 20;

// Validate email
if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
    echo "Email is invalid\n";
} else {
    echo "Email is valid\n";
}

// Validate password length
if (strlen($password) < 8) {
    echo "Password too short\n";
} else {
    echo "Password length is okay\n";
}

// Validate age range
if ($age < 18 || $age > 99) {
    echo "Age is invalid\n";
} else {
    echo "Age is valid\n";
}
OutputSuccess
Important Notes

Always sanitize data before validating to avoid security issues.

Use built-in PHP filters when possible for simplicity and reliability.

Regular expressions are powerful but can be tricky; test them carefully.

Summary

Validation checks if data is correct before using it.

Use filter_var for common checks like email and URL.

Use preg_match for custom pattern checks.

Practice

(1/5)
1.

Which PHP function is commonly used to validate if a string is a valid email address?

easy
A. preg_match with '/^\d+$/'
B. filter_var with FILTER_VALIDATE_EMAIL
C. strlen to check length
D. strtolower to convert to lowercase

Solution

  1. Step 1: Understand email validation in PHP

    PHP provides a built-in filter called FILTER_VALIDATE_EMAIL to check if a string is a valid email.

  2. Step 2: Identify the correct function usage

    filter_var with FILTER_VALIDATE_EMAIL returns the email if valid, or false if invalid.

  3. Final Answer:

    filter_var with FILTER_VALIDATE_EMAIL -> Option B

  4. Quick Check:

    Email validation = filter_var with FILTER_VALIDATE_EMAIL [OK]
Hint: Use filter_var with FILTER_VALIDATE_EMAIL for email checks [OK]
Common Mistakes:
  • Using preg_match with wrong regex for email
  • Checking length instead of format
  • Using string functions unrelated to validation
2.

Which of the following is the correct syntax to validate a URL using filter_var in PHP?

?
easy
A. filter_var($url, FILTER_VALIDATE_INT);
B. filter_var($url, FILTER_VALIDATE_EMAIL);
C. filter_var($url, FILTER_VALIDATE_URL);
D. filter_var($url, FILTER_VALIDATE_BOOLEAN);

Solution

  1. Step 1: Identify the filter for URL validation

    FILTER_VALIDATE_URL is the correct filter to check if a string is a valid URL.

  2. Step 2: Confirm correct function call

    filter_var takes the variable and the filter constant as parameters.

  3. Final Answer:

    filter_var($url, FILTER_VALIDATE_URL); -> Option C

  4. Quick Check:

    URL validation = filter_var with FILTER_VALIDATE_URL [OK]
Hint: Use FILTER_VALIDATE_URL with filter_var for URL validation [OK]
Common Mistakes:
  • Using FILTER_VALIDATE_EMAIL for URLs
  • Using integer or boolean filters incorrectly
  • Missing the filter parameter
3.

What will be the output of the following PHP code?

$phone = '123-456-7890';
if (preg_match('/^\d{3}-\d{3}-\d{4}$/', $phone)) {
    echo 'Valid phone';
} else {
    echo 'Invalid phone';
}
medium
A. Syntax error
B. Invalid phone
C. No output
D. Valid phone

Solution

  1. Step 1: Analyze the regex pattern

    The pattern /^\d{3}-\d{3}-\d{4}$/ matches exactly 3 digits, a dash, 3 digits, a dash, then 4 digits.

  2. Step 2: Check the input string against the pattern

    The string '123-456-7890' matches this pattern exactly.

  3. Final Answer:

    Valid phone -> Option D

  4. Quick Check:

    Regex matches phone format = Valid phone [OK]
Hint: Match exact pattern with preg_match regex anchors ^ and $ [OK]
Common Mistakes:
  • Forgetting anchors ^ and $ in regex
  • Using wrong quantifiers in regex
  • Not escaping special characters
4.

Identify the error in this PHP code snippet for validating an integer:

$num = '123a';
if (filter_var($num, FILTER_VALIDATE_INT)) {
    echo 'Valid integer';
} else {
    echo 'Invalid integer';
}
medium
A. filter_var returns false for '123a', so output is 'Invalid integer'
B. filter_var should use FILTER_VALIDATE_NUMBER instead
C. The variable $num should be cast to int before validation
D. filter_var does not validate integers

Solution

  1. Step 1: Understand filter_var with FILTER_VALIDATE_INT

    This filter returns the integer value if valid, or false if invalid.

  2. Step 2: Check input '123a'

    The string '123a' is not a valid integer, so filter_var returns false.

  3. Final Answer:

    filter_var returns false for '123a', so output is 'Invalid integer' -> Option A

  4. Quick Check:

    Invalid integer string returns false = 'Invalid integer' output [OK]
Hint: filter_var returns false if input is not a pure integer string [OK]
Common Mistakes:
  • Using FILTER_VALIDATE_NUMBER which does not exist
  • Casting before validation causing wrong results
  • Assuming filter_var always returns boolean
5.

You want to validate a username in PHP that must start with a letter, can contain letters, numbers, underscores, and be 5 to 15 characters long. Which preg_match pattern correctly validates this?

hard
A. /^[a-zA-Z][a-zA-Z0-9_]{4,14}$/
B. /^[0-9][a-zA-Z0-9_]{4,14}$/
C. /^[a-zA-Z0-9_]{5,15}$/
D. /^[a-zA-Z]{5,15}$/

Solution

  1. Step 1: Understand username requirements

    Username must start with a letter, then 4 to 14 characters of letters, digits, or underscores, total length 5-15.

  2. Step 2: Analyze each pattern

    /^[a-zA-Z][a-zA-Z0-9_]{4,14}$/ matches a letter at start, then 4-14 allowed chars, total 5-15 length. Others fail start or length rules.

  3. Final Answer:

    /^[a-zA-Z][a-zA-Z0-9_]{4,14}$/ -> Option A

  4. Quick Check:

    Start letter + allowed chars + length 5-15 = /^[a-zA-Z][a-zA-Z0-9_]{4,14}$/ [OK]
Hint: Start with letter, then allowed chars with correct length in regex [OK]
Common Mistakes:
  • Allowing digits as first character
  • Not enforcing length limits
  • Missing anchors ^ and $
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