Archive for November, 2014

Pollution Efficiency of Alternative Fuel Cars

Every now and then, when discussing EVs (electric vehicles) or other alternative fuel cars(1), that offer basically zero pollution (in the form of green house gases and other poisonous gases) someone always raises the argument that these cars just “move the pollution upstream” to the electric power plants and you are still polluting just the same.

But this argument only works if the power production “upstream” really is polluting as much as an onboard gas engine – which really sounds weird to me, because as you increase the success of the engine – from something that had to be small enough to fit in a car to something that basically only had the limit of required to be cost effective – surely you can have large efficiency gains, even if burning the same fuel?

So here are some numbers:


  1. like the new “hydrogen powered” cars []

Script day – Amazon AWS Signature Version 4 With Bash

As anyone who works with the Amazon Web Services API knows, when you submit requests to an AWS service you need to sign the request with your secret key – in order to authenticate your account. The AWS signing process has changed through the years – an earlier version (I think version 1) I implemented in a previous blog post: upload files to Amazon S3 using Bash, with new APIs and newer versions of existing APIs opt in to use the newer signing process.

The current most up to date version of the signing process is known as Signature Version 4 Signing Process and is quite complex, but recently I had the need to use an AWS API that requires requests to be signed using the version 4 process in a bash script(1), so it was time to dust off the old scripting skills and see if I can get this much much much more elaborate signing process to work in bash – and (maybe) surprisingly it is quite doable.

With no further ado, here is the code:


  1. I’m trying to use SQS to send change notifications from a FreeBSD jail running on a FreeNAS server – a place were I’m uncomfortable installing the AWS CLI tool or the SDK. This also help explains all the FreeBSD compatibility written into the code []

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