shell.cpp

#include<stdio.h>
#include<stdlib.h>
#include<sys/wait.h>
#include<unistd.h>
#include<string.h>

void read_command(char cmd[], char *par[]) {
	char line[1024];
	int count = 0, i = 0, j = 0;
	char *array[100], *pch;

	// Read one line
	for (; ;) {
		int c = fgetc(stdin);
		line[count++] = (char) c;
		if (c == '\n')	break;
	}
	if (count == 1)		return;
	pch = strtok(line, "\n");

	// parse the line into words
	while (pch != NULL) {
		array[i++] = strdup(pch);
		pch = strtok(NULL, "\n");
	}

	// first word is the command
	strcpy(cmd, array[0]);

	// others are parameters
	for (int j = 0; j < i; j++)
		par[j] = array[j];
	par[i] = NULL; 		// NULL-terminate the parameter list
}

void type_prompt() {
	static int first_time = 1;
	if (first_time) { 	// clear screen for the first time
		const char* CLEAR_SCREEN_ANSI = "\e[1;1H\e[2J";
		write(STDOUT_FILENO, CLEAR_SCREEN_ANSI, 12);
		first_time=0;
	}
	printf("#");	// display prompt
}

int main() {
	char cmd[100], command[100], *parameters[20];
	// environment variable
	char *envp[] = { (char *) "PATH=/bin", 0 };
	while (1) {		// repeat forever - shell 
		type_prompt(); 	// display prompt on the screen
		read_command(command, parameters);	// read input from the user
		if (fork() != 0)	// parent
			wait(NULL);
		else {
			strcpy(cmd, "/bin/");
			strcat(cmd, command);
			execve(cmd, parameters, envp); 	// execute command
		}
		if (strcmp(command, "exit") == 0)
			break;
	}
	return 0;
}