Overview
A regular expression is a special pattern of characters used to find, match, or replace text in strings.
Think of it like a smart search took - instead of looking for exact words, it can look for patterns like:
- "all emails"
- "every number"
- "any word that ends with
.com" - "dates like 2025-06-27"
Basic Parts of Regular Expressions
Here are some simple and common elements:
| Symbol | Meaning | Example | What it Matches |
|---|---|---|---|
. | Any one character | a.b | aab, acb, a1b |
* | 0 or more of the previous thing | go* | g, go, goo, goooooo |
+ | 1 or more of the previous thing | go+ | go, goo, but not g |
? | 0 or 1 of the previous thing | colou?r | color or colour |
\d | A digit (0-9) | \d\d\d | 123, 456 |
\w | A word character (letter, number, or _) | \w+ | hello123, user_name |
\s | A whitespace (space, tab, etc.) | \s+ | spaces, tabs, etc. |
^ | Start of string | ^Hello | matches strings that start with Hello |
$ | End of string | world$ | matches strings that end with world |
[abc] | One of a, b, or c | gr[ae]y | gray or grey |
[^abc] | Not a, b, or c | [^0-9] | anything thats not a digit |
(abc) | Grouping | (ha)+ | ha, hahaha |
Simple Examples
- Match an email:
/\w+@\w+\.\w+/-> matches things likejohn@example.com - Match a phone number:
/\d{3}-\d{3}-\d{4}/-> matches123-456-7890 - Match a date (YYYY-MM-DD):
/\d{4}-\d{2}-\d{2}/-> matches2025-06-27
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