Jgnore part of tag in expresion

I want to modify my artistsort and composersort actions (simple reversed names of artist and composer) to ignore additional artists/composers.
I use:
$regexp(%composer%,(.) (.),$2',' $1)
Which converts:
Big Bubba
Bubba, Big
and seems to work with most names including initials. I can't make it work with multiple names however. I decided the easiest way was to chose the major artist/composer and include the rest in brackets then include an expression to exclude the bracket contents in the action to reverse the name. I found this:
However I can't figure out where to place it in the expression.
I would prefer a complete expression that sorts by the first artist/composer and ignores the rest. For example:
Artist: Big Bubba, Miss Piggy, Donald Duck
Artistsort: Bubba, Big

Try "Format value" for ARTISTSORT
Format string: $regexp(%artist%,'(.+?) (.+?),.*$','$2, $1')

ARTISTSORT <== $regexp(%ARTIST%,'(.+?)\s(.+?)(,.+?)*$','$2, $1')


Thank you. They both seem to give the intended result. Much appreciated.

Actually this works better because it also works with single artist sort so I don't have to change actions.

EDIT: Is there a way to make this work with artists that have initials?
For example:
Big B. Bubba, Miss Piggy
Bubba, Big B.

At present it formats to:
B. Bubba, Big


ARTIST <== 'Bubba' ARTISTSORT <== $regexp($regexp(%ARTIST%,'^(.+?)(,.+?)$','$1'),'^(.+)\s(.+)$','$2, $1') ARTISTSORT ==> 'Bubba' ARTIST <== 'Big Bubba' ARTISTSORT <== $regexp($regexp(%ARTIST%,'^(.+?)(,.+?)$','$1'),'^(.+)\s(.+)$','$2, $1') ARTISTSORT ==> 'Bubba, Big' ARTIST <== 'Big B. Bubba' ARTISTSORT <== $regexp($regexp(%ARTIST%,'^(.+?)(,.+?)$','$1'),'^(.+)\s(.+)$','$2, $1') ARTISTSORT ==> 'Bubba, Big B.' ARTIST <== 'Big B. Bubba, Miss Piggy, Donald Duck' ARTISTSORT <== $regexp($regexp(%ARTIST%,'^(.+?)(,.+?)$','$1'),'^(.+)\s(.+)$','$2, $1') ARTISTSORT ==> 'Bubba, Big B.' ARTIST <== 'Bubba, Piggy, Duck' ARTISTSORT <== $regexp($regexp(%ARTIST%,'^(.+?)(,.+?)$','$1'),'^(.+)\s(.+)$','$2, $1') ARTISTSORT ==> 'Bubba'


Thanks. This works beautifully.