How to extract string from filename

[Tony Baechler]

Hi all,

The recent discussion on shell scripts got me thinking.  A couple of posters 
invited people to post problems they're having with scripts to the list, so 
here goes.

I have not actually written a script for this because I'm not sure how to go 
about it.  I would normally use cut, but I need to cut from right to left. 
The cut help doesn't indicate a way to do this.  You can only cut from the 
beginning of the line or a range of bytes.  The problem is each line 
(filenames, to be exact) are of different lengths, so it's impossible to 
know what range of bytes I need.

What I'm trying to do is extract the BBC PID from the downloaded files. 
It's a lower case alphanumeric string which starts with a letter and is 
eight characters.  In my case, the first letter is always "b" or "p," so if 
I could use something like grep to just extract the first lower case letter 
followed by a number up to the next underscore, that would be good.  I don't 
think grep will just print a matching phrase, only the matching line.  Here 
are some example filenames:

5_live_Science_-_Coding_and_Computers_b062dj5j_default.mp3
Witness_-_The_Sinking_of_the_USS_Indianapolis_p02wdykn_default.mp3
Discovery_-_A_Scientific_View_of_Agriculture_p0053gbd_default.mp3
Click_-_05_10_2010_p00b18gp_default.mp3

As you can see, they all follow a similar format.  If I could go from right 
to left, I would simply cut "_default.mp3" and extract the preceeding 8 
bytes, but I can't figure out how.  What I'm trying to do is first extract 
the PIDs, hopefully preserving the filenames in the process.  Once they are 
extracted (or printed to stdout), I want to use wget to download the BBC 
programme page.  If you go to www.bbc.co.uk/programme/bXXXXXXX, you'll get a 
web page displaying the broadcast date, description and notes.  I would like 
to download those pages.

Any help with this would be greatly appreciated.  Thanks in advance.

--------------------
Tony Baechler, Baechler Access Technology Services
Putting accessibility at the forefront of technology
mailto:bats at batsupport.com
Phone: 1-619-746-8310   Fax: 1-619-449-9898