Listing object keys programmatically

In Amazon S3, keys can be listed by prefix. You can choose a common prefix for the names of related keys and mark these keys with a special character that delimits hierarchy. You can then use the list operation to select and browse keys hierarchically. This is similar to how files are stored in directories within a file system.

Amazon S3 exposes a list operation that lets you enumerate the keys contained in a bucket. Keys are selected for listing by bucket and prefix. For example, consider a bucket named "dictionary" that contains a key for every English word. You might make a call to list all the keys in that bucket that start with the letter "q". List results are always returned in UTF-8 binary order.

Both the SOAP and REST list operations return an XML document that contains the names of matching keys and information about the object identified by each key.

Groups of keys that share a prefix terminated by a special delimiter can be rolled up by that common prefix for the purposes of listing. This enables applications to organize and browse their keys hierarchically, much like how you would organize your files into directories in a file system.

For example, to extend the dictionary bucket to contain more than just English words, you might form keys by prefixing each word with its language and a delimiter, such as "French/logical". Using this naming scheme and the hierarchical listing feature, you could retrieve a list of only French words. You could also browse the top-level list of available languages without having to iterate through all the lexicographically intervening keys. For more information about this aspect of listing, see Organizing objects using prefixes.

REST API

If your application requires it, you can send REST requests directly. You can send a GET request to return some or all of the objects in a bucket or you can use selection criteria to return a subset of the objects in a bucket. For more information, see GET Bucket (List Objects) Version 2 in the Amazon Simple Storage Service API Reference.

List implementation efficiency

List performance is not substantially affected by the total number of keys in your bucket. It's also not affected by the presence or absence of the prefix, marker, maxkeys, or delimiter arguments.

Iterating through multipage results

As buckets can contain a virtually unlimited number of keys, the complete results of a list query can be extremely large. To manage large result sets, the Amazon S3 API supports pagination to split them into multiple responses. Each list keys response returns a page of up to 1,000 keys with an indicator indicating if the response is truncated. You send a series of list keys requests until you have received all the keys. AWS SDK wrapper libraries provide the same pagination.

Examples

When you list all of the objects in your bucket, note that you must have the s3:ListBucket permission.