Article by Nick Frichette

AWS CLI Tips and Tricks

Standard Input/Output Redirection with "-"

Warning

The following examples have been tested in bash and zsh. Functionality may vary in other shells. If you find these commands work in additional environments, please open a pull request to update this note.

When working in an AWS environment, you may frequently need to view the contents of objects stored in S3. The traditional approach involves a two-step process: using s3:cp to download the file to your local machine, then using cat or a similar tool to view it. While effective, this method can clutter your local system with temporary files and may be slower than necessary.

Fortunately, the AWS CLI allows us to simplify this process by using the - character which represents standard input/output (STDIN/STDOUT). Using -, you can read or write file content directly from or to S3 without creating local copies.

Reading from S3

To read the contents of an object stored in S3 without having to download it first, use the following command:

aws s3 cp s3://bucket-name/object-key -

Example:

nick@host:~$ aws s3 cp s3://hackingthecloud/content -
hacking the cloud

Writing to S3

To upload content directly to an object in S3 without a temporary file, use this command:

echo "hacking the cloud" | aws s3 cp - s3://bucket-name/object-key

This command writes the specified text to an S3 object, again bypassing the need for a local file.

Modifying the CloudTrail Log User-Agent with AWS_EXECUTION_ENV

Shout-out

Shout-out to Christophe Tafani-Dereeper for showing me this.

When making API calls to AWS, a User-Agent header is included in each request, containing details about the client making the request. Although it’s not possible to fully customize this header, you can append information to it, which can be useful for tracking API calls in CloudTrail logs.

One way to modify the User-Agent is by setting the AWS_EXECUTION_ENV environment variable, used by AWS SDKs to identify the execution environment. Tools like grimoire leverage this variable to append custom information to the User-Agent header, making API tracking more informative.