When you need to use preg_match to process text with its supported arguments, it helps to understand both the normal result and what changes with different inputs. This guide focuses on practical examples rather than repeating PHP background material.
preg_match provides the behavior described below. preg_match performs a specific string or regular-expression operation. Read its return value carefully: numeric positions, false, arrays and strings should not be treated as interchangeable.
What Is preg_match in PHP?
Use preg_match to process text with its supported arguments. preg_match performs a specific string or regular-expression operation. Read its return value carefully: numeric positions, false, arrays and strings should not be treated as interchangeable.
Its syntax is:
preg_match(string $pattern, string $subject, &$matches = ..., int $flags = ..., int $offset = ...): int|false
Parameters and return value: Read the argument names and optional values in the signature above. Methods use an existing object, while stand-alone functions take direct arguments. The examples demonstrate the relevant arguments and the value returned or the object modified.
Important: Check the function result using strict comparisons when false and zero are both possible. Multibyte text may require Unicode-aware tools.
Example 1: Basic Usage
This first example demonstrates how to use preg_match to process text with its supported arguments with a small input.
<?php
preg_match("/\d+/", "Order 42", $matches);
print_r($matches);
Output:
Array
(
[0] => 42
)
The example uses the simplest useful form. preg_match performs a specific string or regular-expression operation. Read its return value carefully: numeric positions, false, arrays and strings should not be treated as interchangeable. The output may depend on the active ICU locale, PHP configuration, or input supplied to the function.
Example 2: Another Case
Here the input or option changes, making it easier to see where the behavior differs. Check the function result using strict comparisons when false and zero are both possible. Multibyte text may require Unicode-aware tools.
<?php
echo preg_match("/^hello$/i", "HELLO");
Output:
1
Compare the result to the first example. Related str_* methods process bytes; preg_* methods use regular expressions.
Practical Example: Applying the Function
This standalone example shows how the same operation fits into a small application task.
<?php
$email = "[email protected]";
$validShape = preg_match("/^[^@\s]+@[^@\s]+\.[^@\s]+$/", $email) === 1;
var_dump($validShape);
Output:
bool(true)
The example keeps the operation visible and gives you a starting point for using it in an application. Check the function result using strict comparisons when false and zero are both possible. Multibyte text may require Unicode-aware tools.
Important Behavior and Edge Cases
- Core behavior: preg_match performs a specific string or regular-expression operation. Read its return value carefully: numeric positions, false, arrays and strings should not be treated as interchangeable.
- Return value: Check the result separately from changes to passed-in arrays, iterators, or object state.
- Data constraints: Check the function result using strict comparisons when false and zero are both possible. Multibyte text may require Unicode-aware tools.
- Environment: Run this example under a PHP version supporting the API; check results and exceptions before using them.
Comparison With Related Functions
| Function or Approach | When to Use It |
|---|---|
preg_match | Use preg_match to process text with its supported arguments. |
| Related PHP APIs | Related str_* methods process bytes; preg_* methods use regular expressions. |
Common Beginner Mistakes
| Mistake | Correct Approach |
|---|---|
| Assuming the function works on every kind of input | Follow the declared argument types and check the input format before calling it. |
| Ignoring the behavior of the result | Check the function result using strict comparisons when false and zero are both possible. Multibyte text may require Unicode-aware tools. |
| Using the wrong related PHP API | Related str_* methods process bytes; preg_* methods use regular expressions. |
Key Takeaways
preg_matchhelps you use preg_match to process text with its supported arguments.- preg_match performs a specific string or regular-expression operation. Read its return value carefully: numeric positions, false, arrays and strings should not be treated as interchangeable.
- Check the function result using strict comparisons when false and zero are both possible. Multibyte text may require Unicode-aware tools.
- Related str_* methods process bytes; preg_* methods use regular expressions.
preg_match is useful when you need to use preg_match to process text with its supported arguments. Start with the small examples, then adapt the practical example while respecting its input and environment requirements.