Using Laravel for Advanced String Manipulation in PHP/

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Analyzing Different Types of Regular Expressions

Analyzing Different Types of Regular Expressions

Learn and practice different types of regular expressions.

We'll cover the following...

Character classes

A character class allows us to specify which characters are acceptable for any given position. For example, suppose we had the following pattern:

/abc/

We can interpret it as a literal a followed by a literal b followed by a literal c. Suppose we wanted to match all substrings that contained those three characters in any order. We can achieve this using a character class. We define character classes by specifying what characters are allowed between square brackets:

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<?php
$text = 'aaa abc acc cba';
// Returns ["aaa", "abc", "acc", "cba"]
str($text)->matchAll(
    '/[abc][abc][abc]/'
)->all();

We can also use negation to specify that we do not want characters to appear at a specific location. We do this by starting our class with the ^ character:

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<?php
$text = 'aaa abc def cba';
// Returns ["aaa"]
str($text)->matchAll(
    '/[abc][^be][abc]/'
)->all();

In the code above, our regular expression can be interpreted as:

  • The character a, b, or c followed by
    • Any character that is not b or e`, followed by
      • The character a, b, or c.

If we wanted to include the ^ character itself in our character class, we need to add it to the end of the character class so it is not interpreted as the negation operator:

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<?php
$text = 'aaa abc a^b cba';
// Returns ["a^b"]
str($text)->matchAll(
    '/[abc][z^][abc]/'
)->all();

We can also specify ranges of characters when defining our character classes. This helps to avoid having to write every possible combination of characters. For example, we could rewrite our previous patterns using ranges like so:

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<?php
$text = 'aaa abc acc cba';
// Returns ["aaa", "abc", "acc", "cba"]
str($text)->matchAll(
    '/[a-c][a-c][a-c]/'
)->all();
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