What are basic regex concepts?

Here are some basic concepts of regular expressions (regex):

1. Literals: Characters that match themselves. For example, the regex cat matches the string "cat".

2. Metacharacters: Special characters that have specific meanings, such as:

   • .: Matches any single character except newline.
   • ^: Matches the start of a string.
   • $: Matches the end of a string.
   • *: Matches zero or more occurrences of the preceding element.
   • +: Matches one or more occurrences of the preceding element.
   • ?: Matches zero or one occurrence of the preceding element.

3. Character Classes: Defined using square brackets [], they match any one of the enclosed characters. For example, [abc] matches "a", "b", or "c".

4. Predefined Character Classes:

   • \d: Matches any digit (equivalent to [0-9]).
   • \D: Matches any non-digit.
   • \w: Matches any word character (alphanumeric plus underscore).
   • \W: Matches any non-word character.
   • \s: Matches any whitespace character (spaces, tabs).
   • \S: Matches any non-whitespace character.

5. Quantifiers: Specify how many times an element can occur:

   • {n}: Exactly n times.
   • {n,}: At least n times.
   • {n,m}: Between n and m times.

6. Groups and Capturing: Parentheses () are used to group patterns and capture the matched content for later use.

7. Alternation: The pipe | acts as a logical OR. For example, cat|dog matches either "cat" or "dog".

8. Escaping: Use a backslash \ to escape metacharacters if you want to match them literally.

These concepts form the foundation of regex and can be combined to create complex patterns for matching strings.