295 lines
9.6 KiB
C
295 lines
9.6 KiB
C
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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#include <fcntl.h>
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#include <ctype.h>
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#define MAX_CMD 1024
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#define MAX_ARGS 64
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#define MAX_PIPES 32
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/* =========================================================
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* 工具函数
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* ========================================================= */
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/* 去除字符串首尾空白字符（在原字符串上修改） */
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char *trim(char *s) {
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while (isspace((unsigned char)*s)) s++;
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if (*s == '\0') return s;
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char *end = s + strlen(s) - 1;
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while (end > s && isspace((unsigned char)*end)) end--;
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*(end + 1) = '\0';
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return s;
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}
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/* 把命令字符串按空格拆成 args[]，返回参数个数 */
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int parse_args(char *cmd, char **args) {
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int argc = 0;
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char *token = strtok(cmd, " \t");
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while (token != NULL && argc < MAX_ARGS - 1) {
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args[argc++] = token;
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token = strtok(NULL, " \t");
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}
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args[argc] = NULL;
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return argc;
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}
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/* =========================================================
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* 第一步辅助函数：split_pipeline
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* 把 "cmd1 | cmd2 | cmd3" 按 '|' 拆成若干段，
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* 存入 segments[]，返回段数。
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* 注意：会修改 buf 的内容（把 '|' 替换为 '\0'）。
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* ========================================================= */
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int split_pipeline(char *buf, char *segments[], int max_segs) {
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int nseg = 0;
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char *seg_start = buf; /* 当前段的起始位置 */
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char *p = buf;
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while (*p != '\0') {
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if (*p == '|') {
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/* 找到管道符：截断当前段，保存去空格后的指针 */
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*p = '\0';
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char *seg = trim(seg_start);
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if (seg[0] != '\0') { /* 跳过空段 */
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if (nseg >= max_segs) {
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fprintf(stderr, "shell: too many pipes (max %d)\n", max_segs);
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return -1;
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}
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segments[nseg++] = seg;
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}
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seg_start = p + 1; /* 下一段从 '|' 后面开始 */
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}
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p++;
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}
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/* 保存最后一段（'|' 后面，或整个命令没有 '|' 时） */
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char *last = trim(seg_start);
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if (last[0] != '\0') {
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segments[nseg++] = last;
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}
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return nseg;
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}
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/* =========================================================
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* 第二步辅助函数：exec_cmd_in_child
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* 在子进程里执行一条命令，处理 < 和 > 重定向。
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* in_fd / out_fd 来自管道（或 STDIN/STDOUT_FILENO）。
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* 此函数只能在 fork() 后的子进程里调用，内部会 exit()。
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* ========================================================= */
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static void exec_cmd_in_child(char **args, int argc, int in_fd, int out_fd) {
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/* --- 解析重定向符，把 < file 和 > file 从参数里剥离 --- */
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char *infile = NULL;
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char *outfile = NULL;
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char *clean_args[MAX_ARGS];
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int clean_argc = 0;
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for (int i = 0; i < argc; i++) {
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if (strcmp(args[i], "<") == 0 && i + 1 < argc) {
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infile = args[++i]; /* 记录输入文件，跳过文件名 */
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} else if (strcmp(args[i], ">") == 0 && i + 1 < argc) {
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outfile = args[++i]; /* 记录输出文件，跳过文件名 */
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} else {
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clean_args[clean_argc++] = args[i]; /* 普通参数保留 */
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}
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}
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clean_args[clean_argc] = NULL;
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if (clean_argc == 0) exit(0);
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/* --- 设置标准输入 ---
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* 优先级：< 文件重定向 > 管道读端 > 默认终端 stdin */
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if (infile) {
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if (in_fd != STDIN_FILENO) close(in_fd); /* 管道读端不再需要，关掉 */
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int fd = open(infile, O_RDONLY);
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if (fd < 0) { perror("open"); exit(1); }
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dup2(fd, STDIN_FILENO);
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close(fd);
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} else if (in_fd != STDIN_FILENO) {
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dup2(in_fd, STDIN_FILENO);
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close(in_fd);
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}
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/* --- 设置标准输出 ---
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* 优先级：> 文件重定向 > 管道写端 > 默认终端 stdout */
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if (outfile) {
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if (out_fd != STDOUT_FILENO) close(out_fd);
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int fd = open(outfile, O_WRONLY | O_CREAT | O_TRUNC, 0644);
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if (fd < 0) { perror("open"); exit(1); }
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dup2(fd, STDOUT_FILENO);
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close(fd);
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} else if (out_fd != STDOUT_FILENO) {
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dup2(out_fd, STDOUT_FILENO);
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close(out_fd);
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}
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execvp(clean_args[0], clean_args);
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fprintf(stderr, "shell: command not found: %s\n", clean_args[0]);
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exit(127);
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}
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/* =========================================================
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* 第三步辅助函数：run_single
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* 执行单条命令（无管道），fork 一个子进程并等待它结束。
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* ========================================================= */
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static void run_single(char *seg) {
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char buf[MAX_CMD];
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strncpy(buf, seg, MAX_CMD - 1);
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buf[MAX_CMD - 1] = '\0';
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char *args[MAX_ARGS];
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int argc = parse_args(buf, args);
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if (argc == 0) return;
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pid_t pid = fork();
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if (pid < 0) { perror("fork"); return; }
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if (pid == 0) {
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/* 子进程：从终端 stdin 读，输出到终端 stdout */
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exec_cmd_in_child(args, argc, STDIN_FILENO, STDOUT_FILENO);
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}
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/* 父进程：等待子进程结束 */
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waitpid(pid, NULL, 0);
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}
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/* =========================================================
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* 第四步辅助函数：run_pipeline
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* 执行多段管道命令。
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*
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* 核心思路（以 "A | B | C" 为例）：
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*
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* 终端stdin ──> [A] ──pipe0──> [B] ──pipe1──> [C] ──> 终端stdout
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*
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* 1. 创建 nseg-1 个管道（pipe0, pipe1, ...）
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* 2. 依次 fork 每段命令的子进程，子进程拿到自己的 in_fd/out_fd
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* 3. 父进程关闭所有管道端，然后等待全部子进程结束
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* ========================================================= */
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static void run_pipeline(char *segments[], int nseg) {
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int npipes = nseg - 1;
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/* --- 1. 一次性创建所有管道 --- */
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int pipes[MAX_PIPES][2];
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for (int i = 0; i < npipes; i++) {
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if (pipe(pipes[i]) < 0) {
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perror("pipe");
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/* 出错：关闭已创建的管道后返回 */
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for (int j = 0; j < i; j++) {
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close(pipes[j][0]);
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close(pipes[j][1]);
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}
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return;
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}
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}
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/* --- 2. 依次 fork 每段命令的子进程 --- */
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pid_t pids[MAX_PIPES + 1];
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for (int i = 0; i < nseg; i++) {
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/* 确定本段从哪里读、往哪里写：
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* 第一段：从终端 stdin 读
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* 中间段：从上一个管道的读端读，向下一个管道的写端写
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* 最后段：向终端 stdout 写 */
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int in_fd = (i == 0) ? STDIN_FILENO : pipes[i - 1][0];
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int out_fd = (i == nseg - 1) ? STDOUT_FILENO : pipes[i][1];
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/* 解析本段命令的参数 */
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char cbuf[MAX_CMD];
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strncpy(cbuf, segments[i], MAX_CMD - 1);
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cbuf[MAX_CMD - 1] = '\0';
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char *args[MAX_ARGS];
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int argc = parse_args(cbuf, args);
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pid_t pid = fork();
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if (pid < 0) {
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perror("fork");
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/* fork 失败：关闭所有管道，等待已启动的子进程 */
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for (int j = 0; j < npipes; j++) {
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close(pipes[j][0]);
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close(pipes[j][1]);
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}
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for (int j = 0; j < i; j++) waitpid(pids[j], NULL, 0);
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return;
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}
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if (pid == 0) {
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/* 子进程：
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* 关闭所有"不是自己用"的管道端，
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* 防止 EOF 永远不到达读端。 */
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for (int j = 0; j < npipes; j++) {
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if (pipes[j][0] != in_fd) close(pipes[j][0]);
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if (pipes[j][1] != out_fd) close(pipes[j][1]);
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}
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if (argc == 0) exit(0);
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exec_cmd_in_child(args, argc, in_fd, out_fd);
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/* exec_cmd_in_child 内部会 exit，永远不会走到这里 */
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}
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pids[i] = pid; /* 父进程记录子进程 PID */
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}
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/* --- 3. 父进程关闭所有管道端，再统一等待子进程 ---
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* 必须先全部关闭，否则最后一段命令永远读不到 EOF。 */
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for (int i = 0; i < npipes; i++) {
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close(pipes[i][0]);
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close(pipes[i][1]);
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}
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for (int i = 0; i < nseg; i++) {
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waitpid(pids[i], NULL, 0);
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}
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}
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/* =========================================================
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* 顶层入口：execute
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* 只做"分流"：
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* - 把命令行按 '|' 分段
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* - 1 段 → run_single
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* - 多段 → run_pipeline
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* ========================================================= */
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void execute(char *cmdline) {
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char buf[MAX_CMD];
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strncpy(buf, cmdline, MAX_CMD - 1);
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buf[MAX_CMD - 1] = '\0';
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char *segments[MAX_PIPES + 1];
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int nseg = split_pipeline(buf, segments, MAX_PIPES);
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if (nseg <= 0) return; /* 空命令或出错 */
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if (nseg == 1) {
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run_single(segments[0]); /* 普通命令，无管道 */
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} else {
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run_pipeline(segments, nseg); /* 多段管道命令 */
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}
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}
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/* =========================================================
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* main：读取命令行，循环执行
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* ========================================================= */
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int main() {
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char cmdline[MAX_CMD];
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while (1) {
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printf("%% ");
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fflush(stdout);
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if (fgets(cmdline, MAX_CMD, stdin) == NULL) {
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printf("\n");
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break;
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}
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char *cmd = trim(cmdline);
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if (strlen(cmd) == 0) continue;
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if (strcmp(cmd, "exit") == 0 || strcmp(cmd, "logout") == 0) {
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printf("Goodbye!\n");
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break;
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}
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execute(cmd);
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}
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return 0;
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}
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