Скачиваем Youtube плейлист в формате mp3 одним bash-скриптом

#!/bin/bash

usage='usage:
  ./get_youtube_playlist <playlist_id> <target_folder> <num_songs>
    target_folder: (default: songs will be downloaded in current folder)
    num_songs:     number of songs to get (default: 50)

examples:
  ./get_youtube_playlist RD02HIkZaLeuF9k
  ./get_youtube_playlist RD02HIkZaLeuF9k "instrumental hip-hop beats" 10
'

playlist_id=$1
target_folder=$2
num_songs=$3

if [ -z "$playlist_id" ]; then
    echo "$usage"
    exit 1
fi

if ! [[ "$num_songs" =~ ^[0-9]+$ ]] ; then
    num_songs=50
fi

if [ -z "$target_folder" ]; then
    target_folder='./'
elif [ ! -d "$target_folder" ]; then
    echo "Parameter target_folder is incorrect, $usage"
    exit 1
fi


# используем Youtube API для получения списка песен
# https://developers.google.com/youtube/2.0/developers_guide_protocol_playlist_search
youtube_api="`wget -qO- https://gdata.youtube.com/feeds/api/playlists/$(echo $playlist_id)?max-results=$(echo $num_songs)`"
if [ -z "$youtube_api" ]; then
    echo "Playlist ID is incorrect, $usage"
    exit 1
fi

# cписок ID песен помещаем в массив songs
songs=(
    $(echo $youtube_api | \
    grep -P -o "<media:player url='.*?&" | \
    grep -P -o "(\w|-){11}")
)

if [ -z "$songs" ]; then
    echo "Nothing to do, $usage"
    exit 1
fi

# теперь работаем с каждой отдельной песней
for (( i = 1 ; i <= ${#songs[@]} ; i++ ))
do
    youtube_id=${songs[$i-1]}
    track_number=`printf "%0*d" 2 $i`;

    # 1. скачиваем flv
    youtube-dl --audio-format=mp3 -o "$(echo $target_folder)/$(echo $youtube_id).flv" http://youtu.be/$(echo $youtube_id)

    if [ -f "$(echo $target_folder)/$(echo $youtube_id).flv" ]
    then
        # 2. flv -> mp3
        avconv -i "$(echo $target_folder)/$(echo $youtube_id).flv" \
            -y "$(echo $target_folder)/$(echo $track_number). $(echo $youtube_id).mp3" \
            -acodec libmp3lame -ac 2 -ab 128k -vn

        # 3. удаляем flv
        rm "$(echo $target_folder)/$(echo $youtube_id).flv"
    fi
done