Remove last item in string

myString := "S523.WW.E.SIMA"

; 1) Split it into the dot-separated parts,
;    then join it again excluding the last part
parts := StrSplit(myString, ".")
newString := ""
Loop % parts.MaxIndex() - 1
{
    if(StrLen(newString)) {
        newString .= "."
    }
    newString .= parts[A_Index]
}
msgbox % newString

; 2) RegExMatch to extract everything up until the last dot
RegExMatch(myString, "(.*)\.", newString)
msgbox % newString

; 3) RegExReplace to remove everything, starting with the last dot
newString := RegExReplace(myString, "\.[^.]+$", "")
msgbox % newString