Parse RSS with AppleScript (using grep?) - macos

Question

I am trying to write an AppleScript to set my desktop background to the most recent NASA image of the day. I am trying to do this using this RSS feed: https://www.nasa.gov/rss/dyn/lg_image_of_the_day.rss
The last piece of the puzzle is parsing the URL of the image from the rss feed. I assume this should be very possible using grep, but I don't know how to use grep. I did look through the feed, and I know that the URL I want will be the first <link> in the first <item>.
set {year:y, month:m, day:d} to (current date)
set todaydate to d & "\\ " & m & "\\ " & y
log todaydate
set myFile to "/Users/me/Pictures/NASA\\ Image\\ of\\ the\\ Day/" & todaydate & ".jpg"
property RSSURL : "https://www.nasa.gov/rss/dyn/lg_image_of_the_day.rss"
--get the first download link from the rss feed
--ie stuff inside <link> </link> directly after first <item>
set pictureURL to "" --but to the right thing, of course
do shell script "curl -o " & myFile & " " & pictureURL
tell application "Finder" to set desktop picture to POSIX file "myFile"

Answer 1

Victory!!
set {year:y, month:m, day:d} to (current date)
set todaydate to d & "_" & m & "_" & y
log todaydate
set dir to "~/Pictures/NASA_image_of_the_day/"
set myFile to dir & todaydate & ".jpg"
property RSSURL : "https://www.nasa.gov/rss/dyn/lg_image_of_the_day.rss"
set XMLfile to dir & "feed.xml"
do shell script "curl -o " & XMLfile & " " & RSSURL
tell application "System Events"
tell XML file XMLfile
tell XML element "rss"
tell XML element "channel"
tell XML element "item"
tell XML element "enclosure"
set pictureURL to value of XML attribute "url"
end tell
end tell
end tell
end tell
end tell
end tell
--display dialog pictureURL
--display dialog myFile
do shell script "curl -o " & myFile & " " & pictureURL & " -L"
tell application "System Events"
tell every desktop
set picture to myFile
end tell
end tell