Command line - Some questions

The %1 should be wrapped in double quotes in case there's a space in the file path.

But as to multiple selections, this is what I was talking about with "single instance" behavior. What Explorer does is launch the program for each file selected during the right click. The only way to avoid getting a copy of the program per file is single instance. Meaning the first copy of the program to run has to get control of some system object or file. Subsequent copies try and fail, since the first already has the resource. So secondary copies use some means to transfer the command tail to the first copy. The first copy is expecting this and has the mechanism to receive it.

It's tough to do with batch. A better choice may be a scripting language. There ae many free ones. Python, AutoHotkey, VBScript etc..

Passing the command tail uses IPC or InterProcess Communication. There are many methods. Which is "easy" tends to vary with the language used. But you might check some VBScript or Python archives. You might find some already written that may be adaptable to your task.

Edit: this site is a good source:
http://www.planetsourcecode.com/vb/default.asp?lngWId=1

You're welcome. If I did VB regularly I'd be on that planet source code all the time. Many good libraries free to use there.

Ok. Btw if you have Visual Basic I believe it does single instance just by clicking an option. I'm not sure about VB script.

I found one in VBScript"http
? vbscript ? Ensure single instance of the script running at time.

At the bottom of the function where it has the instnace count, test for 1, if first instance overwrite temp file with the file or foldername from the command line. If the count is greater than 1, append file or folder name to the temp file. In the first instance you need to set some timer or other means to guess when additional instances have quit appending data. Next step of main program is to read the temp file and process, then quit.

Code:

If ncount = 1 then
' overwrite file with command tail here
Elseif ncount>1 then
' The script got executed more than once. Script EXIT
' but only after appending command tail to file
' add code to append file with command tail here
wscript.quit

Edit: As good programming practice you would want to return the instance number out of the function(make it a function instead of subroutine etc..) instead of handling everything inside it. But it makes it clearer to show what to do inline I think.