Made this for a friend - generates an xml feed for a podcast directory, didn't exactly finish it...reads id3v1 tags (id3v2 requires external libraries), runs applescript to open iTunes and load feed for testing, serves feed over http (iTunes required)

podcast-feed-generator.sh

#!/bin/bash

# generate an xml podcast file for a directory of files
#
# I parse id3v1 tags but only for the artist and track title,
# most of the samples did not have reliable meta-data, so the 
# file-name is used.
#
# I don't process id3v2 tags because an external library would be needed
# such as id3lib.
#
# requires python or ruby to be installed

# USAGE:
if [ "$1" = "-h" -o "$1" = "--help" ]; then
	echo; echo "Usage: $0 [options]"; echo
	echo -e "Run this script in a directory of mp3s you want to generate \
		a podcast feed for. If you have multiple folders run the script at \
		the top level to generate a feed for the items in the sub-directories."
	echo;
	echo -e "Note that certain assumptions are made, such as the file-name \
		being used for the track title and artist, id3v1 tags are read \
		for these when available. Due to unreliable metadata id3v1 tags \
		aren't read to retrieve other attributes, id3v2 tags are not read \
		at all as an external dependency such as id3lib would be required."
	echo;
	echo "== Options"; echo
	echo -e "Pass the string \"tag\" to try to use id3v1 tags. \
		Depending on the source of the mp3 files, many will not have reliable \
		data. Try generating the feed with \"tag\" and determine whether it \
		is any good."
	exit 0
fi

# to escape HTML entities which can't be in the xml file
RUBY=$(which ruby)
PYTHON=$(which python)
if [ -z "${PYTHON}" -a -z "${RUBY}" ]; then
	echo "ERROR:"
	echo "You need to have Python or Ruby installed to use this script."
	exit 0
fi

# script vars
# ===========
FILENAME="podcast.xml"
URL="http://localhost:8000/"

artist=''
image=''
result=''
id3v1=false
id3v1_extended=false
# rfc-2822 date format
date_to_use=`date "+%a, %b %d %Y %H:%M:%S %z"`

# do you want to try to read id3v1 tags?
if [ "$1" = "tag" ]; then
	use_id3v1=true
else
	use_id3v1=false
fi

# current directory
function get_dir() {
	echo -e "${PWD##*/}"
}

# the local url, substitutes spaces ' ' => '%20'
function local_url() {
	local result="$URL"
	if [[ ! "$2" = "root" ]]; then
		result+=`get_dir`'/'
	fi
	result+=`basename "$1"`
	echo -e "$result" | sed 's/\ /%20/g'
}

# readline -f emulation
function readline_f() {
	echo -e `cd $(dirname "$1"); pwd`/`basename "$1"`
}

# id3v1 processing
function is_id3v1() { 
	if [[ `tail -c 128 "$1" 2>/dev/null | head -c 3` == "TAG" ]]; then id3v1=true
	else id3v1=false; fi
}
# id3v1-extended, how frequent are these? is this actually needed?
function is_id3v1_extended() { 
	if [[ `tail -c 227 "$1" 2>/dev/null | head -c 4` == "TAG+" ]]; then id3v1_extended=true
	else id3v1_extended=false; fi
}

# match text as a capture group and any spaces after it,
# replace match with just the capture group:
function rtrim() { 
	sed 's/\([^ ]*\) *$/\1/';
}

# get rid of quotes, this is currently the source of slowness the script
function escape() {
	local result=`echo $1 | sed s/[\'\"]//g`
	if [ ! -z "${PYTHON}" ]; then
		result=`"${PYTHON}" -c 'import cgi; print cgi.escape('"'$result'"');'`
	elif [ ! -z "${RUBY}" ]; then
		result=`"${RUBY}" -e 'require "cgi"; puts CGI.escapeHTML('"'$result'"');'`
	fi

	echo -e $result
}

# use just the name of the file (no extension)
function file_with_stripped_extension() {
	filename=`basename $1`
	echo -e ${filename%.*}
}

# get the title for id3v1 or id3v1 extended tags
function get_title() {
	local result=''
	if $id3v1; then
		result=`tail -c 125 "$1" | head -c 30 | rtrim`
	elif $id3v1_extended; then
		result=`tail -c 223 "$1" | head -c 60 | rtrim`
	fi

	if [[ -z "$result" ]]; then
		result=`file_with_stripped_extension "$1"` # use the filename	
	fi
	
	echo -e $result
}

# get the artist for id3v1 or id3v1 extended tags
function get_artist() {
	local result=''
	if $id3v1; then
		result=`tail -c 95 "$1" | head -c 30 | rtrim`
	elif $id3v1_extended; then
		result=`tail -c 163 "$1" | head -c 60 | rtrim`
	fi

	# if either of the above failed
	if [[ -z "$result" ]]; then
		# the global $artist is empty, use the current directory name
		if [[ -z "$artist" ]]; then
			result=`get_dir`
		else
			# otherwise use the globally set artist
			result="$artist"
		fi
	fi
	
	echo -e $result
 }

function make_entry() {
	# if it's an id3v1 tag, then try to get relevant info,
	# I ignore track #s due to them not being particularly 
	# reliable (with the examples I'm using)
	if $use_id3v1; then
		echo "BLEH"
		is_id3v1 "$1"
		is_id3v1_extended "$1"
	fi

	title=`get_title "$1"`

	result+="\n<item>"
	result+="\n\t<title>`escape "$title"`</title>"
	result+="\n\t<itunes:author>`escape "$2"`</itunes:author>"

	# image, if available
	if [[ -n "$3" ]]; then
		result+="\n\t<itunes:image href=\"`escape "$(local_url "$3")"`\"/>"
	fi
	
	# no date info, just use the current date
	result+="\n\t<pubDate>$date_to_use</pubDate>"

	# url is the absolute path of the file on the file-system (readlink -f)
	# length is the size in bytes
	result+="\n\t<enclosure url=\"`escape "$(local_url "$1" "$4")"`\" length=\"`command ls -al "$1" | awk '{ print $5 }'`\" type=\"`file -b --mime-type "$1"`\"/>"
	result+="\n</item>"

	#echo -e $result
}

function process_directory() {\
	echo -e "PROCESSING DIRECTORY: $1"

	# get image if one exists, just use the first one we find,
	# even if there are multiple images
	for file in *.png *.jpg; do
		if [[ -f $file ]]; then
			image="$file"
			break
		fi
	done

	# use same artist for the directory
	local artist=`get_artist "$1"`

	# item info..
	# audio files, sorted
	# optionally can add the following: *.mov, *.m4v, *.pdf, *.epub
	# "`command ls *.mp3 *.m4a *.mp4 2>/dev/null | sort -b -f -i`"
	for file in *.mp3 *.m4a *.mp4; do
		if [[ -f $file ]]; then
			make_entry "$file" "$artist" "$image" "$2"
		fi
	done 

	#echo -e "$result"
}

function write_header() {
	result+="<?xml version=\"1.0\" encoding=\"UTF-8\"?>"
	result+="\n<rss xmlns:itunes=\"http://www.itunes.com/dtds/podcast-1.0.dtd\" version=\"2.0\">"
	result+="\n<channel>"

	directory_name=`escape "$(get_dir)"`
	# channel info
	# assume the directory name is the name of the podcast
	result+="\n<title>$directory_name</title>"
	# try to get the artist from an id3 tag if available,
	# otherwise use the directory name
	result+="\n<itunes:author>`escape "$artist"`</itunes:author>"
	# summary and description, use directory name
	result+="\n<itunes:summary>$directory_name</itunes:summary>"
	result+="\n<description>$directory_name</description>"
	if [[ -n "$image" ]]; then
		result+="\n<itunes:image href=\"$image\" />"
	fi
}

function write_footer() {
	result+="\n</channel>"
	result+="\n</rss>"
}

function write_file() {
	# set global artist
	artist="`get_dir`"

	write_header

	# top-level-directory
	process_directory "`pwd`" 'root'

	# process sub-directories
	for dir in *; do
		if [ -d "$dir" ]; then
			cd "$dir"
			process_directory "$dir"
			cd ..
		fi
	done

	write_footer

	echo -e "$result" > $FILENAME
}

# OUTPUT:

echo
echo "GENERATING PODCAST FEED"
echo "======================="
echo "Writing to: $FILENAME"

# write the actual file
write_file

echo "Finished writing to file: $FILENAME"

# don't run any of the crap below...
exit 0

# test feed in iTunes:
if [ ! -z "${PYTHON}" ]; then
	echo
	echo "Attempting to open iTunes to subscribe..."

	# run applescript which opens iTunes and the podcast subscribe window
	`osascript \
	-e 'tell application "iTunes" to activate' \
	-e 'tell application "System Events" to click menu item "Subscribe to \
	Podcast…" of menu "Advanced" of menu bar 1 of process "iTunes"' \
	-e 'tell application "System Events" to tell process "iTunes" to tell \
	window "Subscribe to Podcast" to set value of text field 1 to \
	"'"$URL$FILENAME"'"'` 

	echo
	echo "Starting server..."
	echo "(because the feed cannot be served to iTunes as a file-system path,"
	echo "itunes requires a URL, use $URL$FILENAME)"
	echo
	echo "Press Ctrl-C to stop the server after retrieving episodes in iTunes..."

	# run simple server from directory
	`"${PYTHON}" -m SimpleHTTPServer`
fi