Output escaping with htmlspecialchars in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to escape special HTML characters in the string.

PHP

<?php
$text = "<script>alert('Hi');</script>";
echo [1]($text);
?>

Drag options to blanks, or click blank then click option'

Ahtmlspecialchars

Bhtmlentities

Cstrip_tags

Daddslashes

Attempts:

3 left

💡 Hint

Common Mistakes

Using strip_tags removes tags but does not escape characters.

Using addslashes escapes quotes but not HTML special characters.

The htmlspecialchars function converts special characters to HTML entities, preventing code injection in HTML output.

2fill in blank

medium

Complete the code to escape special characters and convert quotes to HTML entities.

PHP

<?php
$text = 'He said "Hello" & left.';
echo htmlspecialchars($text, [1]);
?>

Drag options to blanks, or click blank then click option'

AENT_NOQUOTES

BENT_IGNORE

CENT_QUOTES

DENT_COMPAT

Attempts:

3 left

💡 Hint

Common Mistakes

Using ENT_NOQUOTES leaves quotes unescaped.

Using ENT_COMPAT escapes only double quotes.

The ENT_QUOTES flag converts both double and single quotes to HTML entities.

3fill in blank

hard

Fix the error in the code to properly escape the output with UTF-8 encoding.

PHP

<?php
$text = '<b>Bold</b> & "Quotes"';
echo htmlspecialchars($text, ENT_QUOTES, [1]);
?>

Drag options to blanks, or click blank then click option'

A"UTF-8"

B"ISO-8859-1"

C"ASCII"

D"UTF-16"

Attempts:

3 left

💡 Hint

Common Mistakes

Using ISO-8859-1 may cause issues with non-Latin characters.

ASCII does not support special characters beyond basic English.

Using "UTF-8" ensures correct encoding of multibyte characters when escaping HTML.

4fill in blank

hard

Fill both blanks to escape the string and prevent double encoding.

PHP

<?php
$text = '<a href="test">Link</a>';
echo htmlspecialchars($text, [1], 'UTF-8', [2]);
?>

Drag options to blanks, or click blank then click option'

AENT_QUOTES

BENT_NOQUOTES

Ctrue

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Setting double_encode to true causes already escaped entities to be escaped again.

Using ENT_NOQUOTES leaves quotes unescaped.

Use ENT_QUOTES to escape quotes and false to prevent double encoding.

5fill in blank

hard

Fill all three blanks to create a safe HTML output with escaped text and a newline converted to <br>.

PHP

<?php
$text = "Hello & welcome\nHave a nice day!";
$safe_text = nl2br(htmlspecialchars([1], [2], [3]));
echo $safe_text;
?>

Drag options to blanks, or click blank then click option'

A$text

BENT_QUOTES

C"UTF-8"

DENT_NOQUOTES

Attempts:

3 left

💡 Hint

Common Mistakes

Using ENT_NOQUOTES leaves quotes unescaped.

Not passing the variable to htmlspecialchars causes errors.

Escape the variable $text with ENT_QUOTES and "UTF-8" encoding, then convert newlines to <br> tags.

Practice

1. What is the main purpose of the htmlspecialchars function in PHP?

easy

A. To convert special HTML characters to safe codes to prevent code execution

B. To format numbers for display

C. To connect to a database securely

D. To compress HTML output for faster loading

Solution

1. Step 1: Understand the function's role

   htmlspecialchars changes special characters like <, >, &, " into safe HTML entities.

2. Step 2: Recognize the security benefit

   This prevents browsers from interpreting user input as code, protecting against attacks like XSS.

3. Final Answer:

   To convert special HTML characters to safe codes to prevent code execution -> Option A

4. Quick Check:

   htmlspecialchars protects output = To convert special HTML characters to safe codes to prevent code execution [OK]

Hint: Think: 'Make HTML special chars safe' [OK]

Common Mistakes:

• Confusing with formatting functions
• Thinking it compresses or encrypts output
• Assuming it connects to databases

2. Which of the following is the correct syntax to escape a string $input using htmlspecialchars in PHP?

easy

A. html_escape($input);

B. escape_html($input);

C. htmlspecialchars($input);

D. htmlspecialchars_escape($input);

Solution

1. Step 1: Identify the correct function name

   The PHP function to escape HTML special characters is exactly htmlspecialchars.

2. Step 2: Confirm the syntax

   The function is called with the string variable inside parentheses: htmlspecialchars($input);.

3. Final Answer:

   htmlspecialchars($input); -> Option C

4. Quick Check:

   Correct function name and syntax = htmlspecialchars($input); [OK]

Hint: Use exact function name: htmlspecialchars() [OK]

Common Mistakes:

• Using incorrect function names
• Missing parentheses
• Confusing with other escaping functions

3. What will be the output of the following PHP code?

$input = 'Hello & Welcome';
echo htmlspecialchars($input);

medium

A. Hello & Welcome

B. Hello & Welcome

C. <b>Hello & Welcome</b>

D. <b>Hello & Welcome</b>

Solution

1. Step 1: Understand what htmlspecialchars does to special characters

   The characters <, >, and & are converted to &lt;, &gt;, and &amp; respectively.

2. Step 2: Apply htmlspecialchars to the input string

   The string 'Hello & Welcome' becomes '<b>Hello & Welcome</b>'.

3. Final Answer:

   <b>Hello & Welcome</b> -> Option D

4. Quick Check:

   Special chars escaped = <b>Hello & Welcome</b> [OK]

Hint: Remember: <, >, & become <, >, & [OK]

Common Mistakes:

• Expecting HTML tags to remain unescaped
• Not escaping ampersand (&)
• Confusing output with raw HTML

4. Identify the error in this PHP code snippet:

$text = '';
echo htmlspecialchars $text;

medium

A. Incorrect variable name

B. Missing parentheses when calling htmlspecialchars

C. htmlspecialchars does not escape quotes

D. Missing semicolon after variable assignment

Solution

1. Step 1: Check function call syntax

   Functions in PHP require parentheses around arguments. Here, htmlspecialchars $text; is missing parentheses.

2. Step 2: Confirm other syntax elements

   Variable name and semicolons are correct; quotes are escaped by default.

3. Final Answer:

   Missing parentheses when calling htmlspecialchars -> Option B

4. Quick Check:

   Function calls need parentheses = Missing parentheses when calling htmlspecialchars [OK]

Hint: Always use parentheses when calling functions [OK]

Common Mistakes:

• Calling functions without parentheses
• Assuming quotes are not escaped
• Overlooking semicolon placement

5. You want to safely display user input that may contain HTML tags and quotes. Which htmlspecialchars call correctly escapes all special characters including double and single quotes?

hard

A. htmlspecialchars($input, ENT_QUOTES | ENT_HTML5)

B. htmlspecialchars($input, ENT_NOQUOTES)

C. htmlspecialchars($input, ENT_COMPAT)

D. htmlspecialchars($input)

Solution

1. Step 1: Understand the flags for htmlspecialchars

   ENT_QUOTES escapes both single and double quotes; ENT_HTML5 ensures HTML5 entities.

2. Step 2: Compare options

   htmlspecialchars($input, ENT_QUOTES | ENT_HTML5) uses ENT_QUOTES and ENT_HTML5, escaping all quotes and special chars safely.

3. Final Answer:

   htmlspecialchars($input, ENT_QUOTES | ENT_HTML5) -> Option A

4. Quick Check:

   Use ENT_QUOTES to escape all quotes = htmlspecialchars($input, ENT_QUOTES | ENT_HTML5) [OK]

Hint: Use ENT_QUOTES flag to escape all quotes [OK]

Common Mistakes:

• Using ENT_NOQUOTES which skips quote escaping
• Assuming default escapes single quotes
• Not specifying ENT_HTML5 for modern HTML