#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <termios.h>

struct termios term;
int echoing = 1, gotterm = 0, atexitted = 0;

void set_echo(int which)
{ if (echoing == which)
    return;
  if (! gotterm)
  { int r = tcgetattr(0, & term);
    if (r < 0)
      perror("tcegtattr");
    gotterm = 1; }
  if (which)
    term.c_lflag |= ECHO;
  else
    term.c_lflag &= ~ ECHO;
  int r = tcsetattr(0, 0, & term);
  if (r < 0)
    perror("tcsetattr");
  echoing = which; }

void echo_on(void)
{ set_echo(1); }

void echo_off(void)
{ set_echo(0);
  if (! atexitted)
  { atexit(echo_on);
    atexitted = 1; } }

int main(int argc, char *argv[])
{ char line[1024];
  
  while (1)
  { printf("> ");
    char * s = fgets(line, sizeof(line), stdin);
    if (s == NULL)
    { printf("\n");
      break; }

    int end = strlen(line) - 1;
    while (end >= 0 && line[end] <= ' ')
    { line[end] = '\0';
      end -= 1; }

    if (strcmp(line, "+") == 0)
    { echo_on();
      printf("echo on\n"); }

    else if (strcmp(line, "-") == 0)
    { echo_off();
      printf("echo off\n"); }

    else
      printf("You typed \"%s\"\n", line); } }