支持IO重定向的shell程序

Question

这是一个用C ++创建shell的赋值。

我输入ls | sort它完美无缺。但是当我输入另一个命令（ls | sort | head）时，它无法运行并显示此错误：

error: Resource temporarily unavailable
makefile:8: recipe for target 'test' failed
make: *** [test] Error 1

这是代码

void rePipe(pid_t pid[], vector<Command> cmds, int count)
{
    if(count == cmds.size())
    {
        return;
    }

    pid[count] = fork();

    if (pid[count] < 0)
    {
        perror( "error" );
        exit(1);
    }
    else if (pid[count] == 0)  //child
    {
        if(cmds[count].input)
        {
            int fin = open(cmds[count].inputfile, O_RDONLY, 0666);
            dup2(fin, 0);
            close(fin);
        }
        if(cmds[count].output)
        {
            int fout = open(cmds[count].outputfile, O_WRONLY|O_CREAT, 0666);
            dup2(fout, 1);
            close(fout);
        }

        if(count == (cmds.size() -1) )
        {
            close(cmds[count-1].pipeNum[1]);
            dup2(cmds[count-1].pipeNum[0], 0);
        }
        else
        {
            close(cmds[count-1].pipeNum[1]);

            dup2(cmds[count-1].pipeNum[0], 0);

            dup2(cmds[count].pipeNum[1], 1);
            close(cmds[count].pipeNum[1]);
        }

        execvp (cmds[count].cmd[0], cmds[count].cmd);
        perror("Can't execute" );
        exit(1);
    }
    else
    {
        if(count < (cmds.size() -1))
            rePipe(pid, cmds, count++);

        wait(NULL);
    }


}

void execute(vector<Command> cmds)
{
    int count = 0;

    for(int i=0; i < cmds.size(); ++i)
        pipe(cmds[i].pipeNum);

    pid_t pid[cmds.size()];


    pid[count] = fork();

    if (pid[count] < 0)
    {
        perror( "error" );
        exit(1);
    }
    else if (pid[count] == 0)  //child
    {
        if(cmds[count].input)
        {
            int fin = open(cmds[count].inputfile, O_RDONLY, 0666);
            dup2(fin, 0);
            close(fin);
        }
        if(cmds[count].output)
        {
            int fout = open(cmds[count].outputfile, O_WRONLY|O_CREAT, 0666);
            dup2(fout, 1);
            close(fout);
        }
        if(cmds.size() > 1)
        {
            close(cmds[count].pipeNum[0]);
            dup2(cmds[count].pipeNum[1], 1);
            close(cmds[count].pipeNum[1]);

        }

        execvp (cmds[count].cmd[0], cmds[count].cmd);
        perror("Can't execute" );
        exit(1);
    }
    else //parent
    {
        if(cmds.size() > 1)
        {
            rePipe(pid, cmds, 1);
        }

        for(auto & cmd: cmds)
        {   
            close(cmd.pipeNum[0]);
            close(cmd.pipeNum[1]);
        }

        if ( waitpid( pid[cmds.size() - 1], 0, 0 ) < 0 )
        {
            perror( "Internal error: cannot wait for child." );

            exit(1);
        }

    }
}