The simplest regular expressions consist of literal characters. A literal character is a character that matches itself. For example, the regex «a» will match the first occurrence of the character "a" in a string. Consider the string "Jack is a boy": this pattern will match the "a" after the "J".

It’s important to note that the regex engine doesn’t care where the match occurs within a word unless instructed otherwise. If you want to match entire words, you’ll need to use word boundaries, a concept we’ll cover later.

Similarly, the regex «cat» will match the word "cat" in the string "About cats and dogs." This pattern consists of three literal characters in sequence: «c», «a», and «t». The regex engine looks for these characters in the specified order.

Case Sensitivity

By default, most regex engines are case-sensitive. This means that the pattern «cat» will not match "Cat" unless you explicitly configure the engine to perform a case-insensitive search.