Simple Examples
hello: Matches the string “hello” exactly.123: Matches the string “123” exactly..: Matches any single character.\d: Matches any digit character (0-9).\w: Matches any word character (a-z, A-Z, 0-9, _).\s: Matches any whitespace character (space, tab, newline).
Examples
hello world: Matches the string “hello world” exactly.hello|world: Matches either “hello” or “world”.hello.*: Matches “hello” followed by zero or more characters.hello\s: Matches “hello” followed by a whitespace character.hello\d: Matches “hello” followed by a digit character.hello\w: Matches “hello” followed by a word character.hello\s\d: Matches “hello” followed by a whitespace character and a digit character.
Quantifiers
a+: Matches one or more “a” characters.a*: Matches zero or more “a” characters.a?: Matches zero or one “a” character.a{3}: Matches exactly three “a” characters.a{3,}: Matches three or more “a” characters.a{3,5}: Matches between three and five “a” characters.
Character Classes
[abc]: Matches any of the characters “a”, “b”, or “c”.[^abc]: Matches any character that is not “a”, “b”, or “c”.[a-z]: Matches any lowercase letter.[A-Z]: Matches any uppercase letter.[0-9]: Matches any digit character.[\w]: Matches any word character.[\W]: Matches any non-word character.[\s]: Matches any whitespace character.[\S]: Matches any non-whitespace character.
Anchors
^hello: Matches “hello” at the beginning of a line.world$: Matches “world” at the end of a line.\bhello\b: Matches “hello” as a whole word.\Bhello\B: Matches “hello” not as a whole word.
Groups
(hello): Matches “hello” and captures it as a group.(hello|world): Matches either “hello” or “world”.(?:hello): Matches “hello” but does not capture it as a group.(?=hello): Matches any string that is followed by “hello”.(?!hello): Matches any string that is not followed by “hello”.
Flags
/hello/i: Matches “hello” case-insensitively./hello/g: Matches all occurrences of “hello”./hello/m: Matches “hello” across multiple lines./hello/s: Matches “hello” across multiple lines and allows “.” to match newline characters.
Special Characters
\: Escapes a special character..: Matches any single character except newline characters.^: Matches the beginning of a line.$: Matches the end of a line.*: Matches zero or more of the preceding character.+: Matches one or more of the preceding character.?: Matches zero or one of the preceding character.(: Begins a capturing group.): Ends a capturing group.[: Begins a character class.]: Ends a character class.{: Begins a quantifier.}: Ends a quantifier.|: Matches either the expression before or after the operator./: Begins and ends a regular expression.i: Makes the regex case-insensitive.g: Matches all occurrences of the pattern.m: Makes the^and$anchors match the beginning and end of lines.s: Allows.to match newline characters.\n: Matches a newline character.\r: Matches a carriage return character.\t: Matches a tab character.\v: Matches a vertical tab character.\0: Matches a null character (U+0000 NULL).\xhh: Matches a character with the given hex code (e.g.\x0Amatches a newline character).\uhhhh: Matches a character with the given Unicode code point (e.g.\u0009matches a tab character).\cX: Matches a control character using caret notation (e.g.\cJmatches a newline character).\u{hhhh}: Matches a character with the given Unicode code point (e.g.\u{0009}matches a tab character).
Lookarounds
(?=hello): Positive lookahead. Matches any string that is followed by “hello”.(?!hello): Negative lookahead. Matches any string that is not followed by “hello”.(?<=hello): Positive lookbehind. Matches any string that is preceded by “hello”.(?<!hello): Negative lookbehind. Matches any string that is not preceded by “hello”.
Unicode Categories
\p{L}: Matches any letter character.\p{M}: Matches any combining mark character.\p{Z}: Matches any separator character.\p{S}: Matches any symbol character.\p{N}: Matches any number character.\p{P}: Matches any punctuation character.\p{C}: Matches any control character.\p{Ll}: Matches any lowercase letter.\p{Lu}: Matches any uppercase letter.\p{Lt}: Matches any titlecase letter.\p{L&}: Matches any letter character.\p{Lm}: Matches any modifier letter.\p{Lo}: Matches any other letter character.\p{Mn}: Matches any non-spacing mark character.\p{Mc}: Matches any spacing combining mark character.\p{Me}: Matches any enclosing mark character.\p{Zs}: Matches any space separator character.\p{Zl}: Matches any line separator character.\p{Zp}: Matches any paragraph separator character.\p{Sm}: Matches any mathematical symbol character.\p{Sc}: Matches any currency symbol character.\p{Sk}: Matches any modifier symbol character.\p{So}: Matches any other symbol character.\p{Nd}: Matches any decimal digit character.\p{Nl}: Matches any letter number character.\p{No}: Matches any other number character.\p{Pc}: Matches any connector punctuation character.\p{Pd}: Matches any dash punctuation character.\p{Ps}: Matches any open punctuation character.\p{Pe}: Matches any close punctuation character.\p{Pi}: Matches any initial punctuation character.\p{Pf}: Matches any final punctuation character.\p{Po}: Matches any other punctuation character.\p{Cc}: Matches any control character.\p{Cf}: Matches any format character.\p{Cs}: Matches any surrogate character.\p{Co}: Matches any private-use character.\p{Cn}: Matches any unassigned code point.
POSIX Classes
[:alnum:]: Matches any alphanumeric character.[:alpha:]: Matches any alphabetic character.[:ascii:]: Matches any ASCII character.[:blank:]: Matches any whitespace character.[:cntrl:]: Matches any control character.[:digit:]: Matches any digit character.[:graph:]: Matches any visible character.[:lower:]: Matches any lowercase character.[:print:]: Matches any printable character.[:punct:]: Matches any punctuation character.[:space:]: Matches any whitespace character.[:upper:]: Matches any uppercase character.[:word:]: Matches any word character.[:xdigit:]: Matches any hexadecimal digit character.