How do you construct a read-write pipe with lua?

Question

I\'d like to do the equivalent of:

foo=$(echo \"$foo\"|someprogram)

within lua -- ie, I\'ve got a variable containing a bunch of text, and

Answer 1

It's easy, no extensions necessary (tested with lua 5.3).

#!/usr/bin/lua
-- use always locals
local stdin = io.stdin:lines()
local stdout = io.write

for line in stdin do
    stdout (line)
end 

save as inout.lua and do chmod +x /tmp/inout.lua

20:30 $ foo=$(echo "bla"|  /tmp/inout.lua)
20:30 $ echo $foo
bla