get last modified object from S3 CLI

Question

I have a use case where I programmatically bring up an EC2 instance, copy an executable file from S3, run it and shut down the instance (done in user-data). I need to get only the last added file from S3.

Is there a way to get the last modified file / object from a S3 bucket using the AWS CLI tool?

Answer 1

You can list all the objects in the bucket with aws s3 ls $BUCKET --recursive:

$ aws s3 ls $BUCKET --recursive
2015-05-05 15:36:17          4 an_object.txt
2015-06-08 14:14:44   16322599 some/other/object
2015-04-29 12:09:29      32768 yet-another-object.sh

They're sorted alphabetically by key, but that first column is the last modified time. A quick sort will reorder them by date:

$ aws s3 ls $BUCKET --recursive | sort
2015-04-29 12:09:29      32768 yet-another-object.sh
2015-05-05 15:36:17          4 an_object.txt
2015-06-08 14:14:44   16322599 some/other/object

tail -n 1 selects the last row, and awk '{print $4}' extracts the fourth column (the name of the object).

$ aws s3 ls $BUCKET --recursive | sort | tail -n 1 | awk '{print $4}'
some/other/object

Last but not least, drop that into aws s3 cp to download the object:

$ KEY=`aws s3 ls $BUCKET --recursive | sort | tail -n 1 | awk '{print $4}'`
$ aws s3 cp s3://$BUCKET/$KEY ./latest-object

Answer 2

Updated answer

After a while there is a small update how to do it a bit elegant:

aws s3api list-objects-v2 --bucket "my-awesome-bucket" --query 'sort_by(Contents, &LastModified)[-1].Key' --output=text

Instead of extra reverse function we can get last entry from the list via [-1]

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Old answer

This command just do the job without any external dependencies:

aws s3api list-objects-v2 --bucket "my-awesome-bucket" --query 'reverse(sort_by(Contents, &LastModified))[:1].Key' --output=text