Escaping Special Characters in PHP Regex

Suppose we want a special character to represent itself. To do this, it must be escaped with a backslash. Let's look at some examples.

Example

In the following example, the regex author wanted the search pattern to look like this: the letter 'a', then a plus '+', then the letter 'x'. However, the code author did not escape the '+' character, so the search pattern actually looks like this: the letter 'a' one or more times, then the letter 'x':

As a result, the following will be written to the variable:

Example

Now the author has escaped the plus with a backslash. Now the search pattern looks as it should: the letter 'a', then a plus '+', then the letter 'x'.

As a result, the following will be written to the variable:

Example

In this example, the pattern looks like this: the letter 'a', then a dot '.', then the letter 'x':

As a result, the following will be written to the variable:

Example

In the next example, the author forgot to escape the slash and the regex matched all substrings, because an unescaped dot represents any character:

As a result, the following will be written to the variable:

Example

Note that if you forget the backslash for a dot (when it should represent itself) - you might not even notice it:

Visually it works correctly (since the dot represents any character, including a regular dot '.'). But if we change the string in which the replacements occur - we will see our mistake: