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7 Invaluable Techniques to Improve Regex Performance

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Regular expressions or ‘regex’ for short, are very powerful but using them needs a lot of practice. Because of how most regex engines operate, it becomes surprisingly easy to create a regular expression that will take a long time to run. It’s important for you to learn certain techniques that will improve regex performance to make your regex run faster and more effectively.

Why do you need to improve your Regex performance?

Having a well-organized regex engine allows you to look at your pattern while being more forgiving. As an analogy, try to picture a town. The engine recognizes a lot of foreigners in town and even if you cannot express yourself well to them, they can still appreciate your effort. They will try to understand what you’re saying to make communication work between you.

Optimizing your regex expressions means learning tricks and techniques to “speak” to uncivilized or impolite regex engines. Therefore, optimizing your regex compels you to write expressions that are much harder to read and write. 

Of course, this can be a little bit unfair too. Despite all of this, studying how to optimize your regex can be a fun and useful experience. A study of optimization will help deepen your comprehension of how the engine works and this knowledge will enable you to construct your expressions more accurately and at a faster rate.

Read Also: Top 20 MCQ Questions on POSIX Regular Expressions in PHP

How to improve Regex performance?

Whenever you have to deal with regex, you will always want to improve its performance. For this, you can make your own regular expressions cheat sheet that includes the following techniques:

1. Character Classes

This is perhaps the most crucial thing to remember when writing performance regexes. Character classes specify which characters you are or aren’t trying to match. The more specific you are, the better. Using a specific character class gives you control over the number of characters that will cause the regex engine to use, thus, allowing you to prevent rampant backtracking.

2. Ordering Alterations

This happens when a regex has two or more valid options separated by the “|” character. The order also matters if you have several lookbehinds and lookaheads. Your objective is to arrange each option in such a way that it minimizes the amount of work that the regex engine must perform. For alterations, you should prioritize the most common option, followed by the rarer options. If you do it the other way around, the regex engine will have to take time checking the rarer options before checking more common options, which have a higher likelihood of success.

3. Expose Literal Characters

When literal characters and anchors appear in the main pattern instead of getting buried in sub-expressions, the regex engines can make matches faster. Therefore, it’s recommended to expose these literal characters whenever you can by taking them out of a quantified expression or an alteration.

4. Anchors and Boundaries

These inform the regex engine that you want the cursor to be in a certain place in the string. The “$” and “^” are the most common anchors, which indicate a line’s beginning and end. Common boundaries are the non-word boundary “\B” and the word boundary “\b.” Use anchors whenever possible, especially when considering the effect on performance.

Read Also: Top 20 MCQ Questions on Perl Regular Expressions in PHP

5. Lazy Quantifiers

This is a huge performance enhancer. In several naive regexes, you can safely replace greedy quantifiers (*’s) using lazy quantifiers (*? ’s). This gives the regex a performance boost without altering the result.

6. Possessive Quantifiers

You denote possessive quantifiers with a “+”) sign while you denote atomic groups with “?>…”). These two have the same function. After consuming text, they won’t let go. 

This can be a significant advantage for performance reasons since it helps reduce backtracking. But your regex already has to be fairly specific for you to use atomic groups. As such, your performance boost won’t be as much. However, the possessive quantifier can be surprisingly useful.

7. Practice Benchmarking

All regex engines vary from one another. They utilize various algorithms, have varying internal organizations and different sets of operators. You need to know their characteristics and the benchmark on the engine to use for the regex engine to become efficient. 

It takes time to write a precise pattern but this helps prevent your engine from backtracking. Benchmarking requires more effort, but this helps in preventing the degradation of performance on production. 

Furthermore, an understanding of the regex engine implementation will take you away from coding, but it will provide you more confidence in terms of using tools.


Regex performance is a very interesting subject. For many, they only use regex in special circumstances where they need to solve specific types of issues. Under normal conditions, it really will not matter if a regex doesn’t run as fast. Those who develop latency-sensitive applications don’t like to use regex because of their notoriously slow character. But if the regex is the only tool that can get the job done, you can use the tips you learned here.

James Dorian is a technical copywriter. He is a tech geek who knows a lot about modern apps that will make your work more productive. James reads tons of online blogs on technology, business, and ways to become a real pro in our modern world of innovations.

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