Regular expressions
Regular expression, often shorted to regex, is a standard
Syntax
x
, y
, and z
when used under symbols are placeholders for text. Capital X
s, Y
s, and Z
s are used for number placeholders.
Symbol(s) | Name | Description | Example |
---|---|---|---|
Groups and backreferences | |||
(x) |
Capture group | Separates the content in the output. | "Foo Bar" /(Foo)|(Bar)/g -> [ "Foo", "Bar" ]
|
(?:x) |
Non-capture group | Acts as if the parentheses were not there | "Foo Bar" /(?:Foo)|(?:Bar)/g -> [ "Foo Bar" ]
|
(?<y>x) |
Named capture group | Equivalent to (x) , except it remembers the content used. |
"Foo Bar" /(?<F>Foo)|(?<B>Bar)/g -> [ "Foo", "Bar" ]
|
\k<y> |
Named backreference | References a previous named capture group, note that \k is literal |
"Foo Foo" /(?<Foo>Foo)\s\k<Foo>/g -> [ "Foo Foo" ]
|
Character classes | |||
[x-z] |
Character class | Matches every letter or number from x to z . |
"Foo Bar" /[a-f]/gi -> [ "F", "B", "a" ]
|
[xyz] |
References either x , y , or z |
"Foo Bar" /[FB]/g -> [ "F", "B" ]
| |
[^x-z] |
Negated character class | Matches every letter or number not from x to z . |
"Foo Bar" /[^a-f]/gi -> [ "o", "o", " ", "r" ]
|
[^xyz] |
References characters that aren't x , y , or z |
"Foo Bar" /[^FB]/g -> [ "o", "o", " ", "a", "r" ]
| |
. |
Wildcard | Matches every character besides line terminators. Line terminators include \n , \r , \u2028 , and \u2029 |
"Foo Bar" /./g -> [ "F", "o", "o", " ", "B", "a", "r" ]
|
x|y |
Disjunction | Match something or something else. | "Foo Bar" /Foo|Bar/g -> [ "Foo", "Bar" ]
|
\ |
Escape character | If a character is reserved for regex, such as * , | , or . . Note that this is itself a reserve character, so to match for it, you need to use \\ . |
"Foo.bar apple 78.9 banana" /[A-Za-z0-9]*\.[A-Za-z0-9]*/g -> [ "Foo.bar", "78.9" ]
|
Flags
Flag | Name | Description |
---|---|---|
g |
g lobal |
Search all of a string, rather than stopping once you find an occurrence. |