Even this post is real old, but I would like to add that I use powershell to copy files between AWS S3 and my local machine. Here is an example:

$accessKey = 'keyinfo'
$secretKey = 'secretekey'
$region = 'us-east-1'
$bucket = 'bucketname'
$keyPrefix = '/foldernameinAWS/'
$localPath = 'C:\SQLBackups\'

$objects = Get-S3Object -BucketName $bucket -KeyPrefix $keyPrefix -AccessKey $accessKey -SecretKey $secretKey -Region $region | Sort-Object LastModified -descending | Select-Object -First 1 | select key

foreach($object in $objects) {
    $localFileName = $object.Key -replace $keyPrefix, ''
    if ($localFileName -ne '') {
        $localFilePath = Join-Path $localPath $localFileName
        Copy-S3Object -BucketName $bucket -Key $object.Key -LocalFile $localFilePath -AccessKey $accessKey -SecretKey $secretKey -Region $region
    }
}