Upload to S3 via shell script without aws-cli, possible?

As the title says, is it possible to upload to S3 via shell script without aws-cli-tools?

If so, how?

What I'm trying to do is read from a txt file on S3 (which is public, so no authentication is required).

But I want to be able to overwrite whatever is in the file (which is just a number).

Thanks in advance,

Fadi