A Blackmagic Design Fusion LUA script example to check the current comp's flow area for the currently selected Loader/Saver nodes.

FusionFileSelection.lua

-- Find out if we are running Fusion 6, 7, or 8
local fu_major_version = math.floor(tonumber(eyeon._VERSION))

-- Find out the current operating system platform. The platform local variable should be set to either "Windows", "Mac", or "Linux".
local platform = ""
if string.find(fusion:MapPath("Fusion:\\"), "Program Files", 1) then
  -- Check if the OS is Windows by searching for the Program Files folder
  platform = "Windows"
elseif string.find(fusion:MapPath("Fusion:\\"), "PROGRA~1", 1) then
  -- Check if the OS is Windows by searching for the Program Files folder
  platform = "Windows"
elseif string.find(fusion:MapPath("Fusion:\\"), "Applications", 1) then
  -- Check if the OS is Mac by searching for the Applications folder
  platform = "Mac"
else
  platform = "Linux"
end


-- Find out the current directory from a file path
-- Example: print(dirname("/Users/Shared/file.txt"))
function dirname(mediaFileName)
-- LUA dirname command inspired by Stackoverflow code example:
-- http://stackoverflow.com/questions/9102126/lua-return-directory-path-from-path
  sep = ''
  
  if platform == "Windows" then
    sep = "\\"
  elseif platform == "Mac" then
    sep = "/"
  else
    -- Linux
    sep = "/"
  end
  
  return mediaFileName:match("(.*"..sep..")")
end

-- Lock the comp flow area
composition:Lock()

local mediaFileName = nil
  
-- List the selected Node in Fusion 
selectedNode = comp.ActiveTool

if selectedNode then
  print("[Selected Node] ", selectedNode.Name)

  toolAttrs	= selectedNode:GetAttrs()

  -- Read data from either a the loader and saver nodes
  if toolAttrs.TOOLS_RegID == "Loader" then
    mediaFileName = fusion:MapPath(toolAttrs.TOOLST_Clip_Name[1])
    -- Get the file name from the clip
    print("[Loader Image] ", mediaFileName)
  elseif toolAttrs.TOOLS_RegID == "Saver" then
    mediaFileName = fusion:MapPath(toolAttrs.TOOLST_Clip_Name[1])
    print("[Saver Image] ", mediaFileName)
  else
  end

  -- Launch the viewer tool with this media clip
  if mediaFileName ~= nil then
    if eyeon.fileexists(mediaFileName) then
      -- The code to process the selected image goes here
      print("[Launching Terminal Command] ")
    else
      print("[Media File Missing] ", mediaFileName)
    end
  end
  
else
  print("[Node Selection Required] No media node was selected. Please select and activate a loader or saver node in the flow view.")
end
  
-- unlock the comp flow area
composition:Unlock()

-- End of the script
return