shell.c

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

#define TOK_DELIM " \t\r\n"
#define RED "\033[0;31m"
#define RESET "\e[0m"
#define TK_BUFF_SIZE 1024

char *read_line();
char **split_line(char *);
int dash_exit(char **);
int dash_execute(char **);

char *read_line()
{
	int buffsize = 1024;
	int position = 0;
	char * buffer = malloc(sizeof(char) * buffsize);
	int c;

	if(!buffer)
	{
		fprintf(stderr, "%sdash: Allocation error%s\n", RED, RESET);
		exit(EXIT_FAILURE);
	}

	while(1)
	{
		c = getchar();
		if( c == EOF || c == '\n')
		{
			buffer[position] = '\0';
			return buffer;
		}
		else
		{
			buffer[position] = c;
		}
		position++;

		if(position >= buffsize)
		{
			buffsize += 1024;
			buffer = realloc(buffer, buffsize);

			if(!buffer)
			{
				fprintf(stderr, "dash: Allocation error\n");
				exit(EXIT_FAILURE);
			}
		}
	}
}

char **split_line(char * line)
{
	int buffsize = 1024, position = 0;
	char * * tokens = malloc(buffsize * sizeof(char *));
	char * token;

	if(!tokens)
	{
		fprintf(stderr, "%sdash: Allocation error%s\n", RED, RESET);
		exit(EXIT_FAILURE);
	}
	token = strtok(line, TOK_DELIM);
	while(token != NULL)
	{
		tokens[position] = token;
		position++;

		if(position >= buffsize)
		{
			buffsize += TK_BUFF_SIZE;
			tokens = realloc(tokens, buffsize * sizeof(char *));

			if(!tokens)
			{
				fprintf(stderr, "%sdash: Allocation error%s\n", RED, RESET);
				exit(EXIT_FAILURE);
			}
		}
		token = strtok(NULL, TOK_DELIM);
	}

	tokens[position] = NULL;

	return tokens;
}

int dash_exit(char **args)
{
	return 0;
}

int dash_execute(char **args)
{
	pid_t cpid;
	int status;

	if(strcmp(args[0], "exit") == 0)
	{
		return dash_exit(args);
	}

	cpid = fork();

	if(cpid == 0)
	{
		if(execvp(args[0], args) < 0)
		{
			printf("dash: command not found: %s\n", args[0]);
		}
		exit(EXIT_FAILURE);
	}
	else if(cpid < 0)
	{
		printf(RED "Error forking"
			RESET "\n");
	}
	else
	{
		waitpid(cpid, & status, WUNTRACED);
	}

	return 1;
}

void loop()
{
	char * line;
	char * * args;
	int status = 1;

	do
	{
		printf("> ");
		line = read_line();
		args = split_line(line);
		status = dash_execute(args);
		free(line);
		free(args);
	} while (status);
}

int main() {
	loop();
	return 0;
}