Regex Characters: Mastering Literal Matches and Case Sensitivity

Learn the fundamentals of regex with a focus on literal characters and case sensitivity. Understand how to precisely match text patterns and customize regex behavior with case-insensitivity in your programming projects.

Characters in Regex: Building the Foundation

Understanding Literal Characters

At its core, a regular expression (regex) is a sequence of characters. These characters, often referred to as literal characters, are matched literally in the input text. For instance, the regex /cat/ will match the exact sequence "cat" within a string.

Case Sensitivity

By default, regex is case-sensitive. This means that /cat/ will not match "Cat" or "CAT". However, many programming languages offer flags or modifiers to make regex case-insensitive.

Special Characters

While most characters match themselves directly, some have special meanings in regex. These are called metacharacters. They don't match themselves literally but represent pattern-matching constructs. We'll delve deeper into metacharacters in the next section.

Escape Sequences

To match a literal special character, you need to escape it using a backslash (\). This tells the regex engine to treat the following character as a literal rather than a metacharacter.

Common Escape Sequences

• \n: Newline
• \r: Carriage return
• \t: Tab
• \s: Whitespace
• \d: Digit (equivalent to [0-9])
• \w: Word character (letters, digits, underscore)
• \D: Non-digit
• \W: Non-word character
• .: Matches any character except newline

Examples

/\$100/: Matches the exact string "$100"
/\d+/: Matches one or more digits
/\w+/: Matches one or more word characters

"$100", "12345", "Hello123"

Table of Character Matches

Key Points

• Literal characters match themselves directly.
• Regex is case-sensitive by default.
• Special characters have specific meanings in regex.
• Use backslash to escape special characters.

Conclusion

By understanding these foundational concepts, you're well-prepared to explore the power of metacharacters and build more complex regex patterns.