Normal characters
| Expression | Description |
|---|---|
. or [^\n\r] | any character excluding a newline or carriage return |
[A-Za-z] | alphabet |
[a-z] | lowercase alphabet |
[A-Z] | uppercase alphabet |
\d or [0-9] | digit |
\D or [^0-9] | non-digit |
_ | underscore |
\w or [A-Za-z0-9_] | alphabet, digit or underscore |
\W or [^A-Za-z0-9_] | inverse of \w |
\S | inverse of \s |
Whitespace characters
| Expression | Description |
|---|---|
| space |
\t | tab |
\n | newline |
\r | carriage return |
\s | space, tab, newline or carriage return |
Character set
| Expression | Description |
|---|---|
[xyz] | either x, y or z |
[^xyz] | neither x, y nor z |
[1-3] | either 1, 2 or 3 |
[^1-3] | neither 1, 2 nor 3 |
- Think of a character set as an
ORoperation on the single characters that are enclosed between the square brackets. - Use
^after the opening[to “negate” the character set. - Within a character set,
.means a literal period.
Characters that require escaping
Outside a character set
| Expression | Description |
|---|---|
\. | period |
\^ | caret |
\$ | dollar sign |
| | pipe |
\\ | back slash |
\/ | forward slash |
\( | opening bracket |
\) | closing bracket |
\[ | opening square bracket |
\] | closing square bracket |
\{ | opening curly bracket |
\} | closing curly bracket |
Inside a character set
| Expression | Description |
|---|---|
\\ | back slash |
\] | closing square bracket |
- A
^must be escaped only if it occurs immediately after the opening[of the character set. - A
-must be escaped only if it occurs between two alphabets or two digits.
Quantifiers
| Expression | Description |
|---|---|
{2} | exactly 2 |
{2,} | at least 2 |
{2,7} | at least 2 but no more than 7 |
* | 0 or more |
+ | 1 or more |
? | exactly 0 or 1 |
- The quantifier goes after the expression to be quantified.
Boundaries
| Expression | Description |
|---|---|
^ | start of string |
$ | end of string |
\b | word boundary |
- How word boundary matching works:
- At the beginning of the string if the first character is
\w. - Between two adjacent characters within the string, if the first character is
\wand the second character is\W. - At the end of the string if the last character is
\w.
- At the beginning of the string if the first character is
Matching
| Expression | Description |
|---|---|
foo|bar | match either foo or bar |
foo(?=bar) | match foo if it’s before bar |
foo(?!bar) | match foo if it’s not before bar |
(?<=bar)foo | match foo if it’s after bar |
(?<!bar)foo | match foo if it’s not after bar |
Grouping and capturing
| Expression | Description |
|---|---|
(foo) | capturing group; match and capture foo |
(?:foo) | non-capturing group; match foo but without capturing foo |
(foo)bar\1 | \1 is a backreference to the 1st capturing group; match foobarfoo |
- Capturing groups are only relevant in the following methods:
string.match(regexp)string.matchAll(regexp)string.replace(regexp, callback)
\Nis a backreference to theNthcapturing group. Capturing groups are numbered starting from 1.
References and tools
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