PHP Regular Expressions
PHP Regular Expressions (Regex)
Regular Expressions are patterns used to match, search, or replace text.
PHP supports regex in two ways:
preg_ functions → recommended (Perl-compatible)
ereg_ functions → deprecated (not used today)
We use preg_ functions for all modern PHP regex operations.
PHP Regex Functions (preg_)
| Function | Description |
|---|---|
preg_match() | Finds first match |
preg_match_all() | Finds all matches |
preg_replace() | Search & replace |
preg_split() | Split string by regex pattern |
1. preg_match()
Checks if the pattern exists in the string.
Example
/php/i
php→ text to findi→ case-insensitive
2. preg_match_all()
Finds all matches in the string.
Example
Output:
3. preg_replace()
Searches for a pattern and replaces it.
Example
Output:
4. preg_split()
Splits a string using a regex.
Example: split by spaces
Regex Syntax (Common Patterns)
| Pattern | Meaning |
|---|---|
. | any character |
\d | digits (0–9) |
\D | non-digits |
\w | word characters (a-z, A-Z, 0-9, _) |
\W | non-word characters |
\s | whitespace |
\S | non-whitespace |
^ | start of string |
$ | end of string |
[] | a set of characters |
+ | one or more |
* | zero or more |
? | zero or one |
{n} | exactly n times |
{n,} | n or more times |
{n,m} | between n and m times |
Useful Real-World Examples
Validate Email
Validate Mobile Number (10 digits)
Check Username (letters, numbers, underscore)
Extract All Words Starting With Capital Letter
Replace Multiple Spaces with Single Space
Summary
| Function | Purpose |
|---|---|
preg_match() | Find first match |
preg_match_all() | Find all matches |
preg_replace() | Replace text using regex |
preg_split() | Split string |
Regex helps with validation, searching, string cleaning, data extraction, etc.
If you want, I can also provide:
- Regex Cheat Sheet PDF
- Real-world form validation examples
- PHP Regex practice problems
