PHP Regular Expressions (RegEx)

A regular expression is a sequence of characters that forms a search pattern. When you search for data in a text, you can use this search pattern to describe what you are looking for.

1. RegEx Functions

PHP provides several functions that allow you to use regular expressions. The most common ones are:

preg_match() - Returns 1 if the pattern was found in the string and 0 if not.
preg_match_all() - Returns how many times the pattern was found in the string.
preg_replace() - Returns a new string where matched patterns have been replaced with new text.

2. preg_match() Example

The preg_match() function tells you whether a string contains matches of a pattern.

<?php
  $str = "Visit ExpertsJava";
  $pattern = "/expertsjava/i";

  echo preg_match($pattern, $str); // Outputs: 1
?>

3. RegEx Modifiers

Modifiers can change how a search is performed. Common modifiers include:

i - Performs a case-insensitive search.
m - Performs a multi-line search.
u - Enables correct matching of UTF-8 encoded characters.

4. preg_replace() Example

The preg_replace() function replaces all matches of a pattern in a string with another string.

<?php
  $str = "Visit Microsoft!";
  $pattern = "/microsoft/i";

  echo preg_replace($pattern, "ExpertsJava", $str);
  // Outputs: Visit ExpertsJava!
?>

5. RegEx Patterns (Meta-characters)

Meta-characters are characters with a special meaning:

[abc] - Find any character between the brackets.
[^abc] - Find any character NOT between the brackets.
[0-9] - Find any character from 0 to 9.

Tip: The forward slashes / at the start and end of the pattern are called delimiters. They tell PHP where the expression starts and ends.