This works.
=MID(A1,1,LEN(A1)-LEN(MID(A1,FIND(CHAR(1),SUBSTITUTE(A1,"\",CHAR(1),LEN(A1)-LEN(SUBSTITUTE(A1,"\",""))))+1,LEN(A1))))
The above was my original answer. Neil simplified the expression somewhat and posted this as a comment below:
=LEFT(A1,FIND("?",SUBSTITUTE(A1,"\","?",LEN(A1)-LEN(SUBSTITUTE(A1,"\","")))))
This takes advantage of the fact that ?
is a forbidden character in paths so that "?"
can safely be used instead of CHAR(1)
as a placemark, thus improving readability a little bit. Also, LEFT(A1,x)
is equivalent to, and shorter than MID(A1,1,x)
, so it makes sense to use LEFT
. But most importantly, this formula makes use of FIND
, instead of a second layer of counting characters using LEN
. This makes it much more readable.