Arrow keys control in a custom shell using C language

Question

I'm trying to make arrow keys move between characters in a single line (left + right) and between commands from history (up + down) for a custom shell (semester project).

at this point when hitting one of the arrows ^[[A, ^[[B, ^[[C or ^[[D is displayed and after hitting enter I recognize that one of them is hit using:

char a = getchar();

if (a == '\033') {
    getchar();
    int ch2 = getchar();
    switch(ch2){
        case 'A': 
            printf("UP\n"); 
            break;
        case 'B': 
            printf("DOWN\n"); 
            break;
        case 'D': 
            printf("LEFT\n"); 
            break;
        case 'C': 
            printf("RIGHT\n"); 
            break;
        default:
            printf("SOME OTHER SCROLL KEY PRESSED: %d %d\n", a, ch2); 
            break;
    }
}

What I want to get is that as soon as a I hit one of the arrows the action happens without displaying anything.

score 5 · Accepted Answer · answered Oct 14 '19 at 17:39

By default, terminal input in unix systems are line-buffered, you can use termios to specify your own return condition for stdin functions:

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

static struct termios orig_termios;

char get_char_wait_for_keypress(void) {
    struct termios raw;
    // Get stdin file descriptor (0 by default)
    int stdin_fileno = fileno(stdin);
    // Copy terminal io settings
    raw = orig_termios;
    // Set return condition at first byte being received (For input timeout you can use `raw.c_cc[VTIME] = secs`)
    raw.c_cc[VMIN] = 1;
    // Apply settings with new return condition
    tcsetattr(stdin_fileno, TCSANOW, &raw);
    // Get char with new conditions
    char c = getchar();
    // Restore old settings
    tcsetattr(stdin_fileno, TCSANOW, &orig_termios);
    return c;
}

int main(void) {
struct termios raw;
    char c = get_char_wait_for_keypress();
    printf("%d", c);
}

Arrow keys control in a custom shell using C language

1 Answers1