MongoDB: find documents matching regular expression

To find documents matching a regular expression in the MongoDB shell, use the find() method with the $regex operator or a regex literal.

Using a Regex Literal:

JavaScript

db.collectionName.find({ fieldName: /pattern/options });

Example: Find documents in the users collection where the name field contains "john" (case-insensitive).

JavaScript

db.users.find({ name: /john/i });

Using the $regex Operator:

JavaScript

db.collectionName.find({ fieldName: { $regex: "pattern", $options: "options" } });

Example: Find documents in the products collection where the description field contains "eco-friendly" (case-insensitive).

JavaScript

db.products.find({ description: { $regex: "eco-friendly", $options: "i" } });

Explanation:

collectionName: The name of the collection to query.
fieldName: The field within the documents to apply the regular expression to.
pattern: The regular expression pattern to match.
options: Optional flags to modify the regex behavior. Common options include:
- i: Case-insensitive matching.
- m: Multi-line matching.
- s: Allows the dot (.) to match newline characters.
- x: Ignores whitespace characters in the pattern unless escaped.