Regular expression or regex is a very vast topic. We won’t be covering it all in this shot, but it’s still possible to quickly learn something about it.
Objectives: at the end of this shot, you’ll be able to:
- write a basic regex in PHP
- test a regex with
preg_match()function
Let’s get started.
A regular expression, aka regex, is a sequence of characters that represent a pattern. It is also the “language” we use to specify or program patterns for the computer to recognize.
Let’s look at a simple example.
Given the sentence below:
I teach at Educative.
If I want to check if the sentence contains the word “Educative”, I can use it as a pattern like this, /Educative/. You can test this pattern and the sentence in the widget below to see the result.
Note: a pattern is always wrapped by delimiters that can be any sign you want: /, #…
The general syntax is:
/pattern/options
An option or a flag can be, for instance, “i” to ignore the case.
Let’s learn some common patterns you can find out there.
| pattern | description |
|---|---|
\| |
OR, match the first word or the second one, and so on. |
. |
matches only a single character. |
^ |
string start anchor matches the word, but only if it’s at the beginning. |
＄ |
string end anchor matches the word, but only if it’s located at the end. |
Now, let’s use the preg_match() function to perform a regular expression match on a given string. The syntax is as follows:
preg_match(pattern, string)
Example:
preg_match("/PHP|JS/", "I love PHP or Python")
This is how you can read the code above: search “I love PHP or Python” for a match to the regular expression given in “/PHP|JS/”.
Both pattern and string parameters are of type string.
In the exercise below, we will us a ternary operator to print out true or false depending on whether or not there’s a match.
Feel free to modify the code as much as possible until you gain a better understanding of the regex.
<?php/** You can add whatever you want to test regex*/print_r(preg_match("/PHP|JS/", "I love PHP or Python") ? "true" : "false"); // trueecho "<br>";print_r(preg_match("/h./", "hello word!") ? "true" : "false"); // trueecho "<br>";print_r(preg_match("/h./", "Hello word!") ? "true" : "false"); // falseecho "<br>";print_r(preg_match("/^h./i", "Hello word!") ? "true" : "false"); // trueecho "<br>";print_r(preg_match("/word$/", "Hello word!") ? "true" : "false"); // falseecho "<br>";print_r(preg_match("/word.$/", "Hello word!") ? "true" : "false"); // true
Regex is just a special text string used to describe a search pattern that can be any character and/or sequence of symbols (like ., *, etc) wrapped by a deliminator.
To test regex in PHP, use preg_match() as follows:
preg_match(pattern, string)
Now that you understand the regex, write your own regex for the assignment below.
Given the strings below:
sarahmasika@abelmbula.comWrite a regex that:
You can use the widget below to test your solution.
If you are really stuck somewhere, you can find the solutions below.
<?php/** - change "pattern" with your actual pattern and* - the sentence or word with the actual one* - hit the "Run" button to see the result.*/print_r(preg_match("/pattern/", "Word or sentence to search for pattern") ? "true" : "false");
Solutions
Make sure that you’ve tried to find the solution by yourself before you look.