unix shell简单实现，支持参数，管道，重定向

shell.c

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

#define TRUE 1

int main(void) {
    pid_t pid;

    while(TRUE) {
        printf("> ");

        char buf[100];
        if (!fgets(buf, 100, stdin)) return 0;

        char *arg_list[10];
        arg_list[0] = strtok(buf, " \n");
        {
            int i = 0;
            while(arg_list[i] != NULL) {
                i++;
                arg_list[i] = strtok(NULL, " \n");
            }
        }

        pid = fork();
        if (pid == -1) return 1;
        if (pid == 0){

            {// io redirection support
                int i = 0;
                while(arg_list[i] != NULL){
                    char *current_token = arg_list[i];
                    if (strcmp(current_token, ">") == 0){
                        arg_list[i] = NULL; // single command support

                        char *file = arg_list[i+1];
                        if (file == NULL) break;

                        int fd = open(file, O_RDWR | O_CREAT, 0x755);
                        if (fd == -1){
                            printf("%d\n", fd);
                            printf("%s\n", strerror(errno));
                            break;
                        }
                        dup2(fd, STDOUT_FILENO);
                        break;
                    }
                    i++;
                }
            }

            {// pipe
                int i = 0;
                while(arg_list[i] != NULL){
                    char *current_token = arg_list[i];
                    if (strcmp(current_token, "|") == 0){
                        arg_list[i] = NULL; 

                        char ** arg1 = &arg_list[i+1];

                        int fds[2];
                        if (pipe(fds) == -1) break;

                        pid_t pid = fork();
                        if (pid == -1) break;
                        if (pid == 0){
                            close(fds[1]);
                            dup2(fds[0], STDIN_FILENO);
                            execvp(arg1[0], arg1);
                        }else{
                            close(fds[0]);
                            dup2(fds[1], STDOUT_FILENO);
                        }
                        break;
                    }
                    i++;
                }
            }
            execvp(arg_list[0], arg_list);
        }else{
            int status;
            waitpid(-1, &status, 0);
        }
    }
    return 0;
}