Good and Bad PHP Code

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The following is republished from the Tech Times #165.
When interviewing a PHP developer candidate for a job at SitePoint, there is one question that I almost always ask, because their answer tells me so much about the kind of programmer they are. Here’s the question: “In your mind, what are the differences between good PHP code and bad PHP code?” The reason I like this question is because it tests more than just a candidate’s encyclopedic knowledge of PHP’s functions. Zend’s PHP certification does a good job of that (as does the test that Yahoo! issues to applicants for its PHP developer jobs, apparently). Rather, the answer to this question tells me whether a PHP developer has, for example, experienced the pain of working with poorly-written code inherited from a careless predecessor, and whether he or she will go the extra mile to save the rest of the team from that same pain. I don’t have a set notion of the perfect answer to the question, but I do know the kinds of things I’m hoping to hear. Just off the top of my head: Good PHP code should be structured. Long chunks of code can be broken up into functions or methods that achieve sub-tasks with simple code, while non-obvious snippets should be commented to make their meaning plain. As much as possible, you should separate frontend HTML/CSS/JavaScript code from the server-side logic of your applications. PHP’s object oriented programming features give you some especially powerful tools to break up your applications into sensible units. Good PHP code should be consistent. Whether that means setting rules for the names of variables and functions, adopting standard approaches to recurring tasks like database access and error handling, or simply making sure all of your code is indented the same way, consistency makes your code easier for others to read. Good PHP code should be portable. PHP has a number of features, such as magic quotes and short tags, that can break fragile code when they are switched on or off. If you know what you’re doing, however, you can write code that works by adapting to its environment. Good PHP code should be secure
. While PHP offers excellent performance and flexibility out of the box, it leaves important issues like security entirely in the hands of the developer. A deep understanding of potential security holes like Cross-Site Scripting (XSS), Cross-Site Request Forgeries (CSRF), code injection vulnerabilities, and character encoding loopholes is essential for a professional PHP developer these days. Once a candidate has answered this question, I usually have a pretty good idea of whether they’ll be hired or not. Of course, there’s always the possibility that an interviewee simply isn’t able to articulate these types of things, so we also have our candidates sit a PHP developer exam. Many of the questions in this exam seem straightforward on the surface, but they give candidates plenty of opportunity to show how much they care about the little details. The following “bad” code is a highly simplified example of the sort of thing we might put in our PHP developer exam. The question might be something like “How would you rewrite this code to make it better?”
echo("<p>Search results for query: " .
    $_GET['query'] . ".</p>");
The main problem in this code is that the user-submitted value ($_GET['query']) is output directly to the page, resulting in a Cross Site Scripting (XSS) vulnerability. But there are plenty of other ways in which it can be improved. So, what sort of answer are we hoping for? Good:
echo("<p>Search results for query: " .
    htmlspecialchars($_GET['query']) . ".</p>");
This is the least we expect. The XSS vulnerability has been remedied using htmlspecialchars to escape dangerous characters in the submitted value. Better:
if (isset($_GET['query']))
  echo '<p>Search results for query: ',
      htmlspecialchars($_GET['query'], ENT_QUOTES), '.</p>';
Now this looks like someone we might want to hire:
  • The “short” opening PHP tag (<?) has been replaced with the more portable (and XML-friendly) <?php form.
  • Before attempting to output the value of $_GET['query'], isset is used to verify that it actually has a value.
  • The unnecessary brackets (()) around the value passed to echo have been removed.
  • Strings are delimited by single quotes instead of double quotes to avoid the performance hit of PHP searching for variables to interpolate within the strings.
  • Rather than using the string concatenation operator (.) to pass a single string to the echo statement, the strings to be output by echo are separated by commas for a tiny performance boost.
  • Passing the ENT_QUOTES argument to htmlspecialchars to ensure that single quotes (') are also escaped isn’t strictly necessary in this case, but it’s a good habit to get into.
Somewhat distressingly, the number of PHP developers looking for work that are able to give a fully satisfactory answer to this sort of question—at least here in Melbourne—are few and far between. We spent a good three months interviewing for this latest position before we found someone with whom we were happy! So, how would you do when asked a question like this one? Are there any factors that make PHP code good or bad that you feel I’ve left out? And what else would you look for in a PHP developer?

Frequently Asked Questions about Good and Bad PHP Code

What are some common mistakes in PHP coding?

PHP is a powerful scripting language, but it’s also easy to make mistakes if you’re not careful. Some common mistakes include not using proper error reporting, not validating or sanitizing user inputs, using outdated PHP functions, and not using prepared statements for SQL queries. These mistakes can lead to security vulnerabilities, poor performance, and other issues. It’s important to keep up-to-date with best practices and to always test your code thoroughly.

How can I improve my PHP coding skills?

Improving your PHP coding skills involves a combination of learning and practice. Start by studying the basics of PHP, including its syntax, data types, and control structures. Then, move on to more advanced topics like object-oriented programming, error handling, and security. Practice by working on small projects or contributing to open-source projects. Additionally, consider getting a mentor or joining a PHP community where you can learn from others.

What are the best practices for PHP coding?

Best practices for PHP coding include using a consistent coding style, commenting your code, using error reporting during development, validating and sanitizing user inputs, using prepared statements for SQL queries, and keeping your PHP version up-to-date. These practices can help you write code that is secure, efficient, and easy to maintain.

What are some examples of bad PHP code?

Bad PHP code can take many forms. It might involve using outdated PHP functions, not using error reporting, not validating or sanitizing user inputs, or not using prepared statements for SQL queries. These practices can lead to security vulnerabilities, poor performance, and other issues. It’s important to learn from these mistakes and to always strive to write high-quality PHP code.

How can I refactor bad PHP code?

Refactoring bad PHP code involves identifying the problems, making a plan to fix them, and then implementing that plan. Start by reviewing the code and looking for common mistakes like not using error reporting, not validating or sanitizing user inputs, or using outdated PHP functions. Then, decide how to fix these issues. This might involve rewriting parts of the code, implementing new features, or changing the way the code is structured. Always test your changes thoroughly to make sure you haven’t introduced new problems.

What is the importance of using the latest PHP version?

Using the latest PHP version is important for several reasons. First, it ensures that you have access to the latest features and improvements. Second, it helps protect your code from security vulnerabilities that have been fixed in newer versions. Finally, it can help improve the performance of your code. Always make sure to test your code thoroughly after upgrading to a new PHP version.

How can I write secure PHP code?

Writing secure PHP code involves following best practices like validating and sanitizing user inputs, using prepared statements for SQL queries, and using proper error reporting. It’s also important to keep your PHP version up-to-date to protect against known security vulnerabilities. Additionally, consider using a security-focused development process that includes regular code reviews and security testing.

What are the benefits of using a PHP framework?

Using a PHP framework can provide several benefits. It can help you write code more quickly and efficiently by providing a structured development process. It can also help improve the security and performance of your code by providing built-in features and optimizations. Finally, it can make it easier to maintain and scale your code by providing a consistent coding style and architecture.

What are some good resources for learning PHP?

There are many resources available for learning PHP. This includes online tutorials, books, video courses, and coding bootcamps. Additionally, consider joining a PHP community or forum where you can ask questions and learn from others. Always make sure to practice what you learn by working on projects or contributing to open-source software.

How can I prepare for a PHP job interview?

Preparing for a PHP job interview involves studying the basics of PHP, practicing your coding skills, and learning about the company you’re interviewing with. Be prepared to answer questions about your experience with PHP, your understanding of best practices, and your problem-solving skills. Additionally, consider doing some practice interviews to help you feel more comfortable.

Kevin YankKevin Yank
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Kevin Yank is an accomplished web developer, speaker, trainer and author of Build Your Own Database Driven Website Using PHP & MySQL and Co-Author of Simply JavaScript and Everything You Know About CSS is Wrong! Kevin loves to share his wealth of knowledge and it didn't stop at books, he's also the course instructor to 3 online courses in web development. Currently Kevin is the Director of Front End Engineering at Culture Amp.

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