Use RestoreObject with an AWS SDK or command line tool

    using System;
    using System.Threading.Tasks;
    using Amazon;
    using Amazon.S3;
    using Amazon.S3.Model;

    /// <summary>
    /// This example shows how to restore an archived object in an Amazon
    /// Simple Storage Service (Amazon S3) bucket.
    /// </summary>
    public class RestoreArchivedObject
    {
        public static void Main()
        {
            string bucketName = "doc-example-bucket";
            string objectKey = "archived-object.txt";

            // Specify your bucket region (an example region is shown).
            RegionEndpoint bucketRegion = RegionEndpoint.USWest2;

            IAmazonS3 client = new AmazonS3Client(bucketRegion);
            RestoreObjectAsync(client, bucketName, objectKey).Wait();
        }

        /// <summary>
        /// This method restores an archived object from an Amazon S3 bucket.
        /// </summary>
        /// <param name="client">The initialized Amazon S3 client object used to call
        /// RestoreObjectAsync.</param>
        /// <param name="bucketName">A string representing the name of the
        /// bucket where the object was located before it was archived.</param>
        /// <param name="objectKey">A string representing the name of the
        /// archived object to restore.</param>
        public static async Task RestoreObjectAsync(IAmazonS3 client, string bucketName, string objectKey)
        {
            try
            {
                var restoreRequest = new RestoreObjectRequest
                {
                    BucketName = bucketName,
                    Key = objectKey,
                    Days = 2,
                };
                RestoreObjectResponse response = await client.RestoreObjectAsync(restoreRequest);

                // Check the status of the restoration.
                await CheckRestorationStatusAsync(client, bucketName, objectKey);
            }
            catch (AmazonS3Exception amazonS3Exception)
            {
                Console.WriteLine($"Error: {amazonS3Exception.Message}");
            }
        }

        /// <summary>
        /// This method retrieves the status of the object's restoration.
        /// </summary>
        /// <param name="client">The initialized Amazon S3 client object used to call
        /// GetObjectMetadataAsync.</param>
        /// <param name="bucketName">A string representing the name of the Amazon
        /// S3 bucket which contains the archived object.</param>
        /// <param name="objectKey">A string representing the name of the
        /// archived object you want to restore.</param>
        public static async Task CheckRestorationStatusAsync(IAmazonS3 client, string bucketName, string objectKey)
        {
            GetObjectMetadataRequest metadataRequest = new GetObjectMetadataRequest()
            {
                BucketName = bucketName,
                Key = objectKey,
            };

            GetObjectMetadataResponse response = await client.GetObjectMetadataAsync(metadataRequest);

            var restStatus = response.RestoreInProgress ? "in-progress" : "finished or failed";
            Console.WriteLine($"Restoration status: {restStatus}");
        }
    }

To create a restore request for an object

The following restore-object example restores the specified Amazon S3 Glacier object for the bucket my-glacier-bucket for 10 days.

aws s3api restore-object \
    --bucket my-glacier-bucket \
    --key doc1.rtf \
    --restore-request Days=10

This command produces no output.

import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.s3.S3Client;
import software.amazon.awssdk.services.s3.model.RestoreRequest;
import software.amazon.awssdk.services.s3.model.GlacierJobParameters;
import software.amazon.awssdk.services.s3.model.RestoreObjectRequest;
import software.amazon.awssdk.services.s3.model.S3Exception;
import software.amazon.awssdk.services.s3.model.Tier;

/*
 *  For more information about restoring an object, see "Restoring an archived object" at
 *  https://docs.aws.amazon.com/AmazonS3/latest/userguide/restoring-objects.html
 *
 *  Before running this Java V2 code example, set up your development environment, including your credentials.
 *
 *  For more information, see the following documentation topic:
 *
 *  https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/get-started.html
 */
public class RestoreObject {
    public static void main(String[] args) {
        final String usage = """

                Usage:
                    <bucketName> <keyName> <expectedBucketOwner>

                Where:
                    bucketName - The Amazon S3 bucket name.\s
                    keyName - The key name of an object with a Storage class value of Glacier.\s
                    expectedBucketOwner - The account that owns the bucket (you can obtain this value from the AWS Management Console).\s
                """;

        if (args.length != 3) {
            System.out.println(usage);
            System.exit(1);
        }

        String bucketName = args[0];
        String keyName = args[1];
        String expectedBucketOwner = args[2];
        Region region = Region.US_EAST_1;
        S3Client s3 = S3Client.builder()
                .region(region)
                .build();

        restoreS3Object(s3, bucketName, keyName, expectedBucketOwner);
        s3.close();
    }

    public static void restoreS3Object(S3Client s3, String bucketName, String keyName, String expectedBucketOwner) {
        try {
            RestoreRequest restoreRequest = RestoreRequest.builder()
                    .days(10)
                    .glacierJobParameters(GlacierJobParameters.builder().tier(Tier.STANDARD).build())
                    .build();

            RestoreObjectRequest objectRequest = RestoreObjectRequest.builder()
                    .expectedBucketOwner(expectedBucketOwner)
                    .bucket(bucketName)
                    .key(keyName)
                    .restoreRequest(restoreRequest)
                    .build();

            s3.restoreObject(objectRequest);

        } catch (S3Exception e) {
            System.err.println(e.awsErrorDetails().errorMessage());
            System.exit(1);
        }
    }
}