This isn't too hard to create, because Amazon has nicely formed URLs which make identifying a specific page easy, and has well-formed HTML that makes it easy to pull out the specific information.
Let's have a look...
My book Wicked Cool Shell Scripts has an ASIN (Amazon Stock Identification Number) of 1593270127.
Based on that, we can create a URL that has the ASIN embedded within to obtain the page that has information on that particular book:
http://www.amazon.com/exec/obidos/
tg/detail/-/asin/ref=nosim
Click on
this link and you'll see, if you add the properly formatted ASIN it takes you to the information page.
That's half the work, right? Now the other half is to figure out how to extract the Amazon Ranking value, and that's surprisingly easy to do:
lynx -dump "$target" | grep -i "Amazon.com Sales Rank"
Where "target" is the URL shown earlier, with the appropriate ASIN. I run this snippet and here's what I see:
* Amazon.com Sales Rank in [69]Books: #51,988
That's what we want, so all we have to do is cut everything out but the numeric value, and that's easily done by noting that there's a "#" prefacing the value and using
cut to split the line at that point.
Here's the full sequence to extract one ranking for one ASIN:
#!/bin/sh
asin=1593270127
target="http://www.amazon.com/exec/obidos/tg/detail/-/$asin/ref=nosim"
lynx -dump "$target" | grep -i "Amazon.com Sales Rank" | \
cut -d# -f2
Run this, and you'll get the current sales rank.
To turn this into a script that loops through a file of ASINs should be straightforward, and to then save the output into a database or, say, comma separated values (CSV) file should be similarly easy.
I hope that gets you on the right track!
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Even better, there's already a website that does this: www.rankforest.com. It tracks thousands of amazon sales ranks for products by the hour and lets you see pretty graphs and charts too.