PHP preg_match_all to find all matches in a string
Jul 10, 2025 pm 01:51 PM
To extract all occurrences of a pattern from a string in PHP, use the preg_match_all function; it scans the string with a regular expression and returns all matches in an array. 1. The syntax is preg_match_all($pattern, $subject, $matches, $flags, $offset), where $pattern is the regex wrapped in delimiters, $subject is the input string, and $matches stores the results. 2. By default, matches are organized with PREG_PATTERN_ORDER, grouping by match index, but PREG_SET_ORDER can group by capture group instead. 3. Full matches are stored in $matches[0], while subgroups are in subsequent indices. 4. Always test patterns in tools like Regex101, use word boundaries when needed, and ensure regex efficiency for large strings. 5. Check if $matches is not empty before processing to avoid errors.
If you're working with PHP and need to extract all occurrences of a pattern from a string, preg_match_all is the function you want. It’s built for exactly this task — scanning through a string and pulling out every match it finds.
How preg_match_all Works
The basic idea behind preg_match_all is that it applies a regular expression to a string and returns all matches in an array. Here's the general syntax:
int preg_match_all ( string $pattern , string $subject , array &$matches [, int $flags = PREG_PATTERN_ORDER [, int $offset = 0 ]] )
$pattern: Your regex pattern (wrapped in delimiters like/)$subject: The string you're searching in$matches: An array that gets filled with results- Optional flags change how matches are organized or retrieved
The function returns the number of full matches found, which can be useful if you just need to count them.
Basic Usage Example
Let's say you want to extract all email addresses from a block of text. You might do something like this:
$text = "Contact us at support@example.com or sales@domain.co.uk."; $pattern = '/\b[\w.-] @[\w.-] \.\w \b/'; preg_match_all($pattern, $text, $matches); print_r($matches[0]);
This will output:
Array
(
[0] => support@example.com
[1] => sales@domain.co.uk
)You’ll notice we used $matches[0]. That’s because preg_match_all stores full matches in the first element of the $matches array by default.
Understanding Match Arrays
By default, preg_match_all organizes results in one of two main ways, depending on the flag you use:
- PREG_PATTERN_ORDER (default): Matches grouped by match index
- PREG_SET_ORDER: Matches grouped by capture group
For example, if your pattern has groups like /(a)(b)/, here's what each structure looks like:
With PREG_PATTERN_ORDER (default):
Array
(
[0] => Array of full matches
[1] => Array of first group matches
[2] => Array of second group matches
)With PREG_SET_ORDER:
Array
(
[0] => Array of first match, including full and groups
[1] => Array of second match, etc.
)Which format you choose depends on how you plan to process the data.
Tips and Common Gotchas
Here are a few practical things to keep in mind when using preg_match_all:
- Always wrap your patterns in delimiters like
/, unless you’re using other characters for special reasons. - Use
\bword boundaries if matching whole words or patterns like emails or URLs to avoid partial matches. - Be careful with greedy vs non-greedy modifiers (
*?,?) if your pattern could accidentally consume more than intended. - If no matches are found,
$matcheswill be an empty array — so always check before looping. - For performance, try to keep your regex as specific as possible, especially with large input strings.
If you're not sure about your pattern, test it in a tool like Regex101 or an online PHP sandbox before integrating it into your app.
Wrapping Up
Using preg_match_all gives you a powerful way to extract repeated patterns from any string in PHP. Whether you're parsing log files, scraping content, or validating input, knowing how to apply regex across entire strings makes this function indispensable. Just remember to pay attention to your regex structure, result formatting, and edge cases — and you’ll be good to go.
That’s pretty much it.
The above is the detailed content of PHP preg_match_all to find all matches in a string. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
How to combine two php arrays unique values?
Jul 02, 2025 pm 05:18 PM
To merge two PHP arrays and keep unique values, there are two main methods. 1. For index arrays or only deduplication, use array_merge and array_unique combinations: first merge array_merge($array1,$array2) and then use array_unique() to deduplicate them to finally get a new array containing all unique values; 2. For associative arrays and want to retain key-value pairs in the first array, use the operator: $result=$array1 $array2, which will ensure that the keys in the first array will not be overwritten by the second array. These two methods are applicable to different scenarios, depending on whether the key name is retained or only the focus is on
How to use php exit function?
Jul 03, 2025 am 02:15 AM
exit() is a function in PHP that is used to terminate script execution immediately. Common uses include: 1. Terminate the script in advance when an exception is detected, such as the file does not exist or verification fails; 2. Output intermediate results during debugging and stop execution; 3. Call exit() after redirecting in conjunction with header() to prevent subsequent code execution; In addition, exit() can accept string parameters as output content or integers as status code, and its alias is die().
Applying Semantic Structure with article, section, and aside in HTML
Jul 05, 2025 am 02:03 AM
The rational use of semantic tags in HTML can improve page structure clarity, accessibility and SEO effects. 1. Used for independent content blocks, such as blog posts or comments, it must be self-contained; 2. Used for classification related content, usually including titles, and is suitable for different modules of the page; 3. Used for auxiliary information related to the main content but not core, such as sidebar recommendations or author profiles. In actual development, labels should be combined and other, avoid excessive nesting, keep the structure simple, and verify the rationality of the structure through developer tools.
How to create an array in php?
Jul 02, 2025 pm 05:01 PM
There are two ways to create an array in PHP: use the array() function or use brackets []. 1. Using the array() function is a traditional way, with good compatibility. Define index arrays such as $fruits=array("apple","banana","orange"), and associative arrays such as $user=array("name"=>"John","age"=>25); 2. Using [] is a simpler way to support since PHP5.4, such as $color
The requested operation requires elevation Windows
Jul 04, 2025 am 02:58 AM
When you encounter the prompt "This operation requires escalation of permissions", it means that you need administrator permissions to continue. Solutions include: 1. Right-click the "Run as Administrator" program or set the shortcut to always run as an administrator; 2. Check whether the current account is an administrator account, if not, switch or request administrator assistance; 3. Use administrator permissions to open a command prompt or PowerShell to execute relevant commands; 4. Bypass the restrictions by obtaining file ownership or modifying the registry when necessary, but such operations need to be cautious and fully understand the risks. Confirm permission identity and try the above methods usually solve the problem.
php raw post data php
Jul 02, 2025 pm 04:51 PM
The way to process raw POST data in PHP is to use $rawData=file_get_contents('php://input'), which is suitable for receiving JSON, XML, or other custom format data. 1.php://input is a read-only stream, which is only valid in POST requests; 2. Common problems include server configuration or middleware reading input streams, which makes it impossible to obtain data; 3. Application scenarios include receiving front-end fetch requests, third-party service callbacks, and building RESTfulAPIs; 4. The difference from $_POST is that $_POST automatically parses standard form data, while the original data is suitable for non-standard formats and allows manual parsing; 5. Ordinary HTM
How to handle File Uploads securely in PHP?
Jul 08, 2025 am 02:37 AM
To safely handle PHP file uploads, you need to verify the source and type, control the file name and path, set server restrictions, and process media files twice. 1. Verify the upload source to prevent CSRF through token and detect the real MIME type through finfo_file using whitelist control; 2. Rename the file to a random string and determine the extension to store it in a non-Web directory according to the detection type; 3. PHP configuration limits the upload size and temporary directory Nginx/Apache prohibits access to the upload directory; 4. The GD library resaves the pictures to clear potential malicious data.
How Do You Pass Variables by Value vs. by Reference in PHP?
Jul 08, 2025 am 02:42 AM
InPHP,variablesarepassedbyvaluebydefault,meaningfunctionsorassignmentsreceiveacopyofthedata,whilepassingbyreferenceallowsmodificationstoaffecttheoriginalvariable.1.Whenpassingbyvalue,changestothecopydonotimpacttheoriginal,asshownwhenassigning$b=$aorp
