### Requires Keyboard Maestro 7.1+ ###

--- GET REQUIRED KM VARIABLES ---

tell application "Keyboard Maestro Engine"
  set mainStr to getvariable "SCPT__MainString"
  set subStr to getvariable "SCPT__StringToFind"
end tell

--- PROCESS THESE KM VARIABLES ---

--- Get Start of StringToFind ---
set posSubStr to offset of subStr in mainStr

--- SET OUTPUT KM VARIABLE ---

tell application "Keyboard Maestro Engine" to setvariable "SCPT__PosSubStr" to posSubStr