Last Updated: November 21, 2025
Regular Expressions (Regex)
Pattern matching with regex
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Basic Syntax
| Item | Description |
|---|---|
.
|
Any single character |
^
|
Start of string |
$
|
End of string |
*
|
0 or more times |
+
|
1 or more times |
?
|
0 or 1 time (optional) |
{n}
|
Exactly n times |
{n,m}
|
Between n and m times |
[abc]
|
Any of a, b, or c |
[^abc]
|
Not a, b, or c |
Character Classes
| Item | Description |
|---|---|
\d
|
Any digit [0-9] |
\D
|
Not a digit |
\w
|
Word character [a-zA-Z0-9_] |
\W
|
Not a word character |
\s
|
Whitespace (space, tab, newline) |
\S
|
Not whitespace |
\b
|
Word boundary |
\B
|
Not word boundary |
Common Patterns
| Pattern | Regex | Matches |
|---|---|---|
Email
|
^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ | user@example.com |
Phone (US)
|
^\d{3}-\d{3}-\d{4}$ | 123-456-7890 |
URL
|
^https?://[\w.-]+\.[a-z]{2,}$ | https://example.com |
Hex Color
|
^#[0-9A-Fa-f]{6}$ | #FF5733 |
IP Address
|
^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$ | 192.168.1.1 |
Date (YYYY-MM-DD)
|
^\d{4}-\d{2}-\d{2}$ | 2024-01-15 |
Groups & Lookahead
| Item | Description |
|---|---|
(abc)
|
Capture group |
(?:abc)
|
Non-capturing group |
(?=abc)
|
Positive lookahead |
(?!abc)
|
Negative lookahead |
a|b
|
Match a or b |
\1
|
Backreference to group 1 |
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