How to extract string from filename

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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@xxxxxxxxxxxxxx
Phone: 1-619-746-8310   Fax: 1-619-449-9898

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