我正在努力用类管道实现一个 shell.

typedef struct {
    char** cmd;
    int in[2];
    int out[2];
} cmdio;

cmdio cmds[MAX_PIPE + 1];

读取管道中的命令并将其存储在cmds中.

cmdio [i] .in是pipe()返回的输入管道的文件描述符对.对于从终端输入读取的第一个命令,它只是{fileno(stdin),– 1}. cmdin [i] .out对输出管道/终端输出类似. cmdio [i] .in与cmd [i-1] .out相同.例如：

$ls -l | sort | wc

CMD: ls -l 
IN: 0 -1
OUT: 3 4

CMD: sort 
IN: 3 4
OUT: 5 6

CMD: wc 
IN: 5 6
OUT: -1 1

我们将每个命令传递给process_command,它执行许多操作：

for (cmdi = 0; cmds[cmdi].cmd != NULL; cmdi++) {
    process_command(&cmds[cmdi]);
}

现在,在process_command中：

if (!(pid_fork = fork())) {
    dup2(cmd->in[0],fileno(stdin));
    dup2(cmd->out[1],fileno(stdout));    
    if (cmd->in[1] >= 0) {
        if (close(cmd->in[1])) {
            perror(NULL);
        }
    }
    if (cmd->out[0] >= 0) {
        if (close(cmd->out[0])) {
            perror(NULL);
        }
    }
    execvp(cmd->cmd[0],cmd->cmd);
    exit(-1);
}

问题是永远从管道中读取：

COMMAND $ls | wc
Created pipe,in: 5 out: 6
Foreground pid: 9042,command: ls,Exited,info: 0
[blocked running read() within wc]

如果,而不是与execvp交换过程,我只是这样做：

if (!(pid_fork = fork())) {
    dup2(cmd->in[0],fileno(stdout));
    if (cmd->in[1] >= 0) {
        if (close(cmd->in[1])) {
            perror(NULL);
        }
    }
    if (cmd->out[0] >= 0) {
        if (close(cmd->out[0])) {
            perror(NULL);
        }
    }

    char buf[6];
    read(fileno(stdin),buf,5);
    buf[5] = '\0';

    printf("%s\n",buf);
    exit(0);
}

它碰巧工作：

COMMAND $cmd1 | cmd2 | cmd3 | cmd4 | cmd5 
Pipe creada,in: 11 out: 12
Pipe creada,in: 13 out: 14
Pipe creada,in: 15 out: 16
Pipe creada,in: 17 out: 18
hola!
Foreground pid: 9251,command: cmd1,info: 0
Foreground pid: 9252,command: cmd2,info: 0
Foreground pid: 9253,command: cmd3,info: 0
Foreground pid: 9254,command: cmd4,info: 0
hola!
Foreground pid: 9255,command: cmd5,info: 0

可能是什么问题呢？

if (!(pid_fork = fork())) {
    dup2(cmd->in[0],cmd->cmd);
    exit(-1);
}

if (!(pid_fork = fork())) {
    dup2(cmd->in[0],fileno(stdout));    
    if (cmd->in[1] >= 0) {
        if (close(cmd->in[1])) {
            perror(NULL);
        }
    }
    if (cmd->out[0] >= 0) {
        if (close(cmd->out[0])) {
            perror(NULL);
        }
    }
    close(cmd->in[0]);  // Or your error checked version,but I'd use a function
    close(cmd->out[1]);     
    execvp(cmd->cmd[0],cmd->cmd);
    exit(-1);
}