Lua - popen 2x '&&' chained set /p - stdout takes a vacation - windows

Question

I'm working in an environment that has approximately zero functional ui while a lua script is running. This just isn't acceptable for the script I need to write, which relies heavily on user input. The only way I've found to circumvent this is using io.popen with some rather crafty commands.
I recognize that what I'm trying to do here is strange and very much wrong, and that I've brought this upon myself, but I can't figure out what's going wrong in this code snippet:
local a = 'f'
local p = io.popen(
'echo -~`~-,_,- Editing '..(a == 'f' and 'foreground' or 'background')..' -~`~-,_,- > con && '.. --display text to the user
'set /p f= Find block: > con < con && '.. --user input
'call echo %f% &&' .. --pass f back to the lua script
'set /p r= Replace with: > con < con && '.. --user input
'call echo %r% &&' .. --pass r back to the lua script
'pause < con', "r")
local f = p:read("*a") --read what was passed back, later parse it back into 2 variables
p:close()
What I expect to happen:
A 'command prompt window' is displayed to the user, asking for input.
The user enters 2 values.
The values are echoed back to the lua script as they are entered.
The values are read from the pipe and stored for later use.
The command line waits for a keypress, and then closes.
What actually happens:
A 'command prompt window' is displayed to the user, asking for input.
The user enters a value for f.
f is echoed back to the lua script.
The user enters a value for r.
r is echoed back to the console. (!!!)
f is read from the pipe. r is not present.
The command line waits for a keypress, and then closes.
This very similar code sample works just fine, but only returns 1 variable:
p = io.popen(
'echo What do you want to do? > con && '..
'echo G: remove girders > con && '..
'echo F: swap foreground > con && '..
'echo B: swap background > con && '..
'echo U: undo all edits > con && '..
'echo C: cancel > con && '..
'set /p a= Choose an option: > con < con && '..
'call echo %a%', "r")
a = string.lower(p:read("*a"):gsub("\n",""))
p:close()
What am I doing wrong, and how can I rewrite this to work for my purposes?
What in the world have I unleashed, and how do I put the genie back into the bottle?

Answer 1

After a good while googling, I found this:
(
echo some output
echo more output
)>"Your logfile
Redirecting Output from within Batch file
I had no clue you could wrap commands like that, and I've been tinkering with the Windows CLI since I first discovered it.
local a = 'f'
local p = io.popen(
'echo -~`~-,_,- Editing '..(a == 'f' and 'foreground' or 'background')..' -~`~-,_,- > con && '.. --display text to the user
'( set /p f= Find block: && '.. --user input
'set /p r= Replace with: ) > con < con && '.. --user input
'call echo %f% &&' .. --pass f back to the lua script
'call echo %r% &&' .. --pass r back to the lua script
'pause < con > con', "r")
local f = p:read("*a") --read what was passed back, later parse it back into 2 variables
p:close()
Wrapping the two set /p statements as above works - I get the expected output of f, followed by a newline, and then r, all sent back to the lua script, where they belong.
Still, if anyone can clue me in on why this was a problem in the first place, I would be very much interested in the explanation.

Answer 2

local p = io.popen(
-- create temporary .bat-file
'set tmpf="%TEMP%\\TMP%RANDOM%.BAT" &&'..
'cmd /c"(echo #set p=^%1&echo #set /p x= ^%p:~1,-1^%^>con&echo #call echo ^%x^%)>%tmpf%" &&'..
-- Your main program
'echo. -~`~-,_,- Editing '..(a == 'f' and 'foreground' or 'background')..' -~`~-,_,- > con &&'.. --display text to the user
'call %tmpf% "Find block:" < con &&'.. -- pass f back to the lua script
'call %tmpf% "Replace with:" < con &&'..-- pass r back to the lua script
-- delete temporary .bat-file
'call del %tmpf% > con &&'..
'pause < con', "r")
local f = p:read'*a'
p:close()