Hello world unix shell

hellosh.c

/* hellosh
 * based on http://stephen-brennan.com/2015/01/16/write-a-shell-in-c/ (first hit on google for "how to write a shell")
 * compile: gcc -o hellosh hellosh.c
 */
#include <sys/wait.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#define SHELL_NAME "hellosh"
#define DELIMITER " \t\r\n\a"
#define BUFFER_SIZE 64


char *read_line() {
	char *line = NULL;
	ssize_t buffer_size = BUFFER_SIZE;
	getline(&line, &buffer_size, stdin);
	return line;
}

char **split(char *string, char *delimiter) {
	ssize_t buffer_size = BUFFER_SIZE;
	char *saveptr;
	char *token = strtok_r(string, delimiter, &saveptr);
	char **tokens = malloc(BUFFER_SIZE * sizeof(char*));
	int i = 0;

	while (token != NULL) {
		tokens[i] = token;
		i++;
		if (i >= buffer_size) {
			buffer_size += BUFFER_SIZE;
			tokens = realloc(tokens, buffer_size * sizeof(char*));
			if (!tokens) {
				fprintf(stderr, "allocation error\n");
				exit(EXIT_FAILURE);
			}
		}
		token = strtok_r(NULL, delimiter, &saveptr);
	}
	tokens[i] = NULL;
	return tokens;
}


int launch(char **command) {
	pid_t pid;
	pid_t wpid;
	int status;

	pid = fork();
	if (pid == 0) {
	  // If failed
		if (execvp(command[0], command) == -1) {
			perror(SHELL_NAME);
		}
		exit(EXIT_FAILURE);
	} else if (pid < 0) {
	  // If successful
		do {
			wpid = waitpid(pid, &status, WUNTRACED);
		} while (!WIFEXITED(status) && !WIFSIGNALED(status));
	}
}


int execute(char **command) {
	if (command[0] == NULL) {
		return 1;
	}
	return launch(command);
}

void loop() {
	char *line;
	char **args;
	int status;
	do {
		printf("> ");
		line = read_line();
		args = split(line, DELIMITER);
		status = execute(args);
		free(line);
		free(args);
	} while (status);
}

int main(int argc, char **argv) {
	loop();
	return EXIT_SUCCESS;
}