用C语言设计简单的命令行myshell代码，并能在实验环境下运行。 要求支持的命令如下： 1. cd [directory] 将当前目录改为 [directory] 2. environ 列出所有环境变量 3. ls 列出指定目录下所有文件 4. help 显示所有支持的命令 5. echo 在屏幕上显示参数并换行 6. quit 退出 shell 7. 支持I/O重定向 8. 常见的目录和文件操作，比如新建目录或文件，目录或文件的删除、复制，显示文件内容等。

以下是一个简单的myshell代码，支持上述要求的命令：

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

#define MAX_CMD_LEN 1024
#define MAX_ARG_NUM 64
#define MAX_PATH_LEN 256

char* envp[];

void print_prompt() {
    char path[MAX_PATH_LEN];
    getcwd(path, MAX_PATH_LEN);
    printf("[myshell]%s$ ", path);
    fflush(stdout);
}

void parse_cmd(char* cmd, char** args, int* redirect_in, int* redirect_out) {
    char* ptr = strtok(cmd, " \t\n");
    int index = 0;
    while (ptr != NULL) {
        if (strcmp(ptr, "<") == 0) {  // 输入重定向
            ptr = strtok(NULL, " \t\n");
            *redirect_in = open(ptr, O_RDONLY);
            if (*redirect_in < 0) {
                perror("open");
                exit(1);
            }
        } else if (strcmp(ptr, ">") == 0) {  // 输出重定向
            ptr = strtok(NULL, " \t\n");
            *redirect_out = open(ptr, O_WRONLY | O_CREAT | O_TRUNC, 0666);
            if (*redirect_out < 0) {
                perror("open");
                exit(1);
            }
        } else {
            args[index++] = ptr;
        }
        ptr = strtok(NULL, " \t\n");
    }
    args[index] = NULL;
}

void exec_cmd(char** args, int redirect_in, int redirect_out) {
    int pid = fork();
    if (pid < 0) {
        perror("fork");
        exit(1);
    } else if (pid == 0) {  // 子进程
        if (redirect_in != 0) {
            dup2(redirect_in, STDIN_FILENO);
            close(redirect_in);
        }
        if (redirect_out != 0) {
            dup2(redirect_out, STDOUT_FILENO);
            close(redirect_out);
        }
        if (execvp(args[0], args) < 0) {
            perror("execvp");
            exit(1);
        }
    } else {  // 父进程
        wait(NULL);
    }
}

void cd(char* path) {
    if (chdir(path) < 0) {
        perror("chdir");
    }
}

void environ() {
    char** env = envp;
    while (*env) {
        printf("%s\n", *env++);
    }
}

void ls(char* path) {
    DIR* dir = opendir(path);
    if (dir == NULL) {
        perror("opendir");
        exit(1);
    }
    struct dirent* entry;
    while ((entry = readdir(dir)) != NULL) {
        printf("%s\n", entry->d_name);
    }
    closedir(dir);
}

void help() {
    printf("cd [directory]: change current working directory\n");
    printf("environ: list all environment variables\n");
    printf("ls [directory]: list all files in directory\n");
    printf("help: display all supported commands\n");
    printf("echo [args]: display arguments on the screen\n");
    printf("quit: exit the shell\n");
}

void echo(char** args) {
    int i = 1;
    while (args[i] != NULL) {
        printf("%s ", args[i++]);
    }
    printf("\n");
}

int main() {
    char cmd[MAX_CMD_LEN];
    char* args[MAX_ARG_NUM];
    int redirect_in, redirect_out;
    while (1) {
        redirect_in = redirect_out = 0;
        print_prompt();
        if (fgets(cmd, MAX_CMD_LEN, stdin) == NULL) {
            printf("\n");
            exit(0);
        }
        parse_cmd(cmd, args, &redirect_in, &redirect_out);
        if (args[0] == NULL) {
            continue;
        }
        if (strcmp(args[0], "cd") == 0) {
            cd(args[1]);
        } else if (strcmp(args[0], "environ") == 0) {
            environ();
        } else if (strcmp(args[0], "ls") == 0) {
            ls(args[1]);
        } else if (strcmp(args[0], "help") == 0) {
            help();
        } else if (strcmp(args[0], "echo") == 0) {
            echo(args);
        } else if (strcmp(args[0], "quit") == 0) {
            exit(0);
        } else {
            exec_cmd(args, redirect_in, redirect_out);
        }
    }
    return 0;
}

编译后直接运行即可。