terminal emulator - lab 3 on "Operating Systems" in MAI

Makefile

all:
	gcc -Wall -std=gnu99 zhell.c -o zhell
clean:
	rm zhell

zhell.c

/*
 * File: zhell.c (14.03.2014)
 * thx for source code shell dwhitney67 (http://ubuntuforums.org/showthread.php?t=931794&p=5869326#post5869326)
 * Copyright 2014 L1S & ahmpro
 */
#include <stdio.h>
#include <signal.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <malloc.h> 
#include <setjmp.h>

pid_t child_pid, back_pid = 0;
pid_t child_active_pid;

void ctrl_c(int sig) {
    switch(sig) {
        case SIGINT:
            if (child_active_pid > 0) {
                kill(child_active_pid, SIGTERM);
                child_active_pid = 0;
            }
            break;
        default:
            break;
            //exit(0);
    }
}

int main()
{
    int status = 0;
    char cmd[512] = {0};

    char **argv = malloc(10 * sizeof(char*));
    int argc;
    char *arg;

    int is_bgr = 0;

    struct sigaction sa;
    memset(&sa, 0, sizeof(sa));
    sa.sa_handler = ctrl_c;
    sigset_t set;
    sigemptyset(&set);
    sigaddset(&set, SIGINT);
    sa.sa_mask = set;
    sigaction(SIGINT, &sa, 0);

    while (1) {
        for (int i = 0; i < argc; ++i) {
            free(argv[i]);
        }
        free(argv);

        is_bgr = 0;
        child_active_pid = 0;
        argc = 0;
        argv = malloc(10 * sizeof(char*));

        printf("zhell (%s) > ",getenv("PWD"));
        if (fgets(cmd, sizeof(cmd), stdin ) == NULL) {
            printf("\n");
            continue;
        }
        cmd[strlen(cmd)-1] = '\0';

        if (!strcmp(cmd, "quit") || !strcmp(cmd, "exit")) {
            break;
        }

        if (!strcmp(cmd, "kill")) {
            back_pid = 0;
        }

        arg = strtok(cmd, " ");
        while (arg != 0 && argc < 9) {
            argv[argc++] = strdup(arg);
            arg = strtok(NULL, " ");
        }
        argv[argc] = 0;

        if (argc > 0) {
            char *last_arg = argv[argc-1];
            if (!strcmp(last_arg, "&")) {
                printf("1\n");
                is_bgr = 1;
                argc--;
                argv[argc] = 0;
            } else if (last_arg[strlen(last_arg)-1] == '&') {
                last_arg[strlen(last_arg)-1] = 0;
                is_bgr = 1;
            }
        } else {
            continue;
        }

        child_pid = fork();

        if (child_pid < 0) {
            perror("Fork failed");
            break;

        } else if (child_pid > 0) {            
            if (is_bgr) {
                back_pid = child_pid;
                child_active_pid = 0;
                waitpid(-1, &status, WNOWAIT);
            } else {
                child_active_pid = child_pid;
                waitpid(-1, &status, 0);
                child_active_pid = 0;
                //printf("Exit status of PID%d was %d\n", (int)child_pid, status);
            }
            continue;

        } else if (child_pid == 0) {
            // execute shell command
            if (argc>0) {
                setpgid(0, 0);
                execvp(argv[0], argv);
            }
            exit(0);
        }
    }
    return 0;
}