I have just written an Applescript that will do just what you are asking. I have posted it here for you. It still needs some work, as in it could be shortened a bit plus some of the code could be technically better but it works.
I had a problem whereby OS X Yosemite would not check for updates on t's own. it would only do so if I did it manually. I tried everything I could think of so finally wrote a script to do so which I then add to a calendar reminder so that on that day/time the script will run triggering the checks. The script get's the settings from the ones you set in app store settings(screen shot above)
hope it helps
-- Apple script to check for Updates in OS X Yosemite.
-- For some reason OS X Yosemite does not do this for all people
-- Copyright Dawson 2015 all rights and copy rights will be retained by me at all times
-- though the user is entitled to make any edits as required
-- tell finder to read the file com.apple.SoftwareUpdate.plist and copy it to a variable.
-- Then take each variable of the file that is used to store choices the user makes as
-- to checking, downloading and installing of updates and copy them to other variables.
-- Then if each of the variables are TRUE get softwareupdate to perfrom that action
tell application "Finder"
set myfile to "/Library/preferences/com.apple.SoftwareUpdate.plist"
set sourcepath to POSIX path of myfile
do shell script "cp -r " & sourcepath's quoted form & " ~/Desktop/"
do shell script "plutil -convert xml1 /Users/touchdown/Desktop/com.apple.SoftwareUpdate.plist"
set myfile to "~/Desktop/com.apple.SoftwareUpdate.plist"
set thetext to (readmyfile)
tell application "System Events"
tell property list filemyfile
tell contents
set automaticcheckenabledcopy to value of property list item "AutomaticCheckEnabled"
if automaticcheckenabledcopy = true then do shell script "softwareupdate -l"
set automaticdownloadcopy to value of property list item "AutomaticDownload"
if automaticdownloadcopy = true then do shell script "softwareupdate -d"
set configdatainstallcopy to value of property list item "ConfigDataInstall"
if configdatainstallcopy = true then do shell script "softwareupdate -i --install -a"
set criticalupdateinstallcopy to value of property list item "CriticalUpdateInstall"
if criticalupdateinstallcopy = true then do shell script "softwareupdate -i --install -r"
end tell
end tell
end tell
do shell script "rm –Rf ~/Desktop/com.apple.SoftwareUpdate.plist"
end tell
