While programming the rotary phone input device, I needed a way to play the latest version of one of my favorite audcasts(yea, I said audcast because it is an audio broadcast and I don't have an ipod). OK enough of that, let's get back to the problem at hand. The audcast uses RSS to publish new episodes of their show, and since an RSS feed is a standarized XML file, I should be able to get all the info I need fairly easily.

The basic functionality that I needed was:

• get the XML text from the URL of the RSS feed
• process the XML text and get the URL of the first audio file in the XML
• play the audio file over the internet; fortunately, I know of a great command-line audio player that can do that. Mplayer will do that as well.

There are some people with powerful command-line foo who could probably write a five line bash script with wget and awk to do this, but I'm not one of those people so I decided to use the Python programming language and the code is as follows:

#!/usr/bin/env python
import sys
#we will need to parse xml
from xml.dom import minidom
#we need to get files from the interpipesnetweb
import urllib
#we want to run a subprocess
import subprocess

#define the parser class
class RSSParser():
    def __init__(self,url):
        self.rssUrl = url

    def getLatest(self):
        try:
            print "checking "+self.rssUrl+"..."
            #read the text from the URL
            rsstext = urllib.urlopen(self.rssUrl)
            print "parsing..."
            #parse the xml from the rss text
            xmlDocElement = minidom.parse(rsstext).documentElement
            #make an array of the enclosure elements
            enclosures = xmlDocElement.getElementsByTagName("enclosure")
            #get the first enclosure
            enclosure = enclosures[0]
            #get the url from the first enclosure
            audio_url = enclosure.attributes['url'].value
            return audio_url
        except:
            return ""
    
if __name__=="__main__":
    #set a default rss url
    rss_url = "http://feeds.feedburner.com/linuxoutlaws-ogg"
    #what shall we use to play the audio?
    audio_player = "sap"
    # has the user requested a different url?
    if len(sys.argv) > 1:
        rss_url = sys.argv[1]
    #make a parser
    parser = RSSParser(rss_url)
    #get the file we want to play
    file_to_play = parser.getLatest()
    #did a file get returned?
    if len(file_to_play) > 0:
        #launch the player with the file to play
        subprocess.call([audio_player,file_to_play])

Well there you have it. Read it, change it, use it.