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Welcome to the world of Regular Expressions! In this introductory article, we'll explore the basic building blocks of regex. Regular expressions, or regex, are a series of characters that form a search pattern, allowing you to match, locate, and manage text. By understanding these simple grammars, you'll be able to harness the full potential of regex with regex.ai.

What is a Regular Expression?

Metacharacters are unique characters that possess specific meanings and play a vital role in defining patterns within regular expressions:
Character
Description
Example
[]
A collection of characters, representing a range or a set of allowed characters
"[Ll]iberty"
\
Indicates a special sequence or is used to escape special characters
"\d{4}"
.
Any character, excluding newline, often used as a wildcard
"La.s"
^
Specifies that the pattern must begin with the given characters
"^Regex"
$
Specifies that the pattern must end with the given characters
"toolbuilder$"
*
Allows zero or more occurrences of the preceding character or group
"Re*gex"
+
Allows one or more occurrences of the preceding character or group
"La+bs"
?
Allows zero or one occurrences of the preceding character or group
"Libert?y"
{}
Precisely the stated number of occurrences of the preceding character or group
"La{2}s"
|
Provides an alternative option between two patterns
"Liberty|Labs"
()
Used to capture and group a portion of the pattern

Special Sequences

A special sequence consists of a \ followed by one of the characters listed below, giving it a unique meaning within the regular expression:
Character
Description
Example
\A
Matches if the specified characters are at the start of the string
"\ALiberty"
\b
Matches if the specified characters are at the beginning or end of a word (use "r" in the beginning for treating the string as a "raw string")
r"\bLabs", r"Regex\b"
\B
Matches if the specified characters are in the string, but NOT at the beginning or end of a word (use "r" in the beginning for treating the string as a "raw string")
r"\BR", r"L\B"
\d
Matches if the string contains digits (numbers 0-9)
"Lab\d"
\D
Matches if the string DOES NOT contain digits
"Regex\D"
\s
Matches if the string contains a white space character
"Liberty\sLabs"
\S
Matches if the string DOES NOT contain a white space character
"toolbuilder\S"
\w
Matches if the string contains any word characters (letters a to Z, digits 0-9, and the underscore _ character)
"Liberty\w"
\W
Matches if the string DOES NOT contain any word characters
“Labs\W"
\Z
Matches if the specified characters are at the end of the string
"toolbuilder\Z"