Character Classes

Pattern	Description
[abc]	Matches any single character inside the brackets.
[^abc]	Matches any single character not inside the brackets.
.	Matches any character except newline characters.
\d	Matches any digit character (0-9).
\D	Matches any non-digit character.
\w	Matches any word character (letters, digits, underscore).
\W	Matches any non-word character.
\s	Matches any whitespace character (spaces, tabs, line breaks).
\S	Matches any non-whitespace character.
\t	Matches a tab character.
\n	Matches a newline character.
\r	Matches a carriage return character.
\uhhhh	Matches a Unicode character specified by the four hexadecimal digits.
\xhh	Matches a character specified by the two hexadecimal digits.

Anchors and Boundaries

Pattern	Description
^	Matches the beginning of a line or string.
$	Matches the end of a line or string.
\b	Matches a word boundary position.
\B	Matches a position that is not a word boundary.

Quantifiers

Pattern	Description
x*	Matches zero or more occurrences of "x".
x+	Matches one or more occurrences of "x".
x?	Matches zero or one occurrence of "x".
x{n}	Matches exactly "n" occurrences of "x".
x{n,}	Matches at least "n" occurrences of "x".
x{n,m}	Matches between "n" and "m" occurrences of "x".
x*?, x+?, x??	Non-greedy versions of the quantifiers.

Groups and Lookarounds

Pattern	Description
(x)	Captures the matched substring.
(?:x)	Groups without capturing.
(?<name>x)	Captures the matched substring into a named group.
\n	Backreference to the nth captured group.
\k<name>	Backreference to a named capturing group.
x(?=y)	Matches "x" only if followed by "y".
x(?!y)	Matches "x" only if not followed by "y".
(?<=y>x)	Matches "x" only if preceded by "y".
(?<!y>x)	Matches "x" only if not preceded by "y".

Special Characters and Escape Sequences

Pattern	Description
x|y	Matches either "x" or "y".
\\	Escapes a special character to treat it literally (e.g., `\*`, `\.`).
\cX	Matches a control character.
\0	Matches a NULL character.