## termios.lua

    #! /usr/bin/env lua

    local M = require 'posix.termio'

    local F = require 'posix.fcntl'
    local U = require 'posix.unistd'

    local dev = arg[1] or '/dev/ttyUSB0'

    -- Open serial port and do settings
    local fds, err = F.open(dev, F.O_RDWR + F.O_NONBLOCK)
    if not fds then
       print('Could not open serial port ' .. dev .. ':', err)
       os.exit(1)
    end

    M.tcsetattr(fds, 0, {
       cflag = M.B115200 + M.CS8 + M.CLOCAL + M.CREAD,
       iflag = M.IGNPAR,
       oflag = M.OPOST,
       cc = {
          [M.VTIME] = 0,
          [M.VMIN] = 1,
       }
    })

    -- Set stdin to non canonical mode. Save current settings
    local save = M.tcgetattr(0)
    M.tcsetattr(0, 0, {
       cc = {
          [M.VTIME] = 0,
          [M.VMIN] = 1
       }
    })

    -- Loop, reading and writing between ports. ^C stops
    local set = {
       [0] = {events={IN=true}},
       [fds] = {events={IN =true}},
    }

    U.write(1, 'Starting terminal, hit ^C to exit\r\n')

    local function exit(msg)
       M.tcsetattr(0, 0, save)
       print '\n'
       print(msg)
       os.exit(0)
    end

    while true do
       local r = require 'posix.poll'.poll(set, -1)
       for fd, d in pairs(set) do
          if d.revents and d.revents.IN then
             if fd == 0 then
                local d, err = U.read(0, 1024)
                if not d then
                   exit(err)
                end
                if d == string.char(3) then
                   exit('Bye')
                end
                local ok, err = U.write(fds, d)
                if not ok then
                   exit(err)
                end
             end
             if fd == fds then
                local d, err = U.read(fds, 1024)
                if not d then
                   exit(err)
                end
                local ok, err = U.write(1, d)
                if not ok then
                   exit(err)
                end
             end
          end
       end
    end

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