如何进行shell重定向C

我有一个标记器，它接收用户的输入。然后我继续扫描“>”或“s”：

---

替换父进程的

stdin

和

stdout

（在

if（pid）

中），并且不会影响子进程。将

dup2

stuff移到

else

分支，就在

execvp

之前，这是在C中执行重定向时应该使用的流

int file_stdin;
int file_stdout;
int file_stderr;

/*--------------------------------------------------------------------
; code to set infile and outfile I'll assume that if redirection isn't
; being used, the appropriate filehandle will be -1.
;
; file_stdin  should be a file that is opened using O_RDONLY.
; file_stdout should be a file that is opened using O_WRONLY.
; file_stdout should be a file that is opened using O_WRONLY.
;
; Be wary of using a file descriptor opened for both reading and writing
; and using the same file descriptor---it will probably not do what you
; expect it to do.
;
; Also note, you can also use file descriptors from the pipe() system
; call (to allow piping from command to command) or network sockets, or
; anything that can be read/written from a file descriptor.
;---------------------------------------------------------------------*/

pid_t child;

child = fork();
if (child < 0)
  report_error(errno);
else if (child > 0)
{
  int status;
  int rc;

  /*------------------------------------------------------------------
  ; wait for the child process.  More code needs to be added to
  ; descriptor errors and what not, but that's left as an exercise for
  ; the reader
  ;-----------------------------------------------------------------*/

  rc = wait(&status);
}
else
{
  /*--------------------------------------------------------------------
  ; child process.  Set up redirection if required.  Once the rediretion
  ; has been set (using dup2()), the original file descriptor is closed   
  ; as it is no longer needed and just wastes file descriptors in the   
  ; child process.
  ;-------------------------------------------------------------------*/

  if (file_stdin > -1)
  {
    dup2(file_stdin,STDIN_FILENO);
    close(file_stdin);
  }

  if (file_stdout > -1)
  {
    dup2(file_stdout,STDOUT_FILENO);
    close(file_stdout);
  }

  if (file_stderr > -1)
  {
    dup2(file_stderr,STDERR_FILENO);
    close(file_stderr);
  }

  /*------------------------------------------------------------------
  ; close any unneeded open files here ... 
  ;------------------------------------------------------------------*/

  /*------------------------------------------------------------------
  ; PROGRAM, ARGV and ENVP need to be replaced with appropriate values
  ;------------------------------------------------------------------*/

  if(execve(PROGRAM,ARGV,ENVP) < 0)
    _exit(EXIT_FAILURE);
}

int文件\u stdin；
int文件标准输出；
int文件\u stderr；
/*--------------------------------------------------------------------
; 设置infile和outfile的代码，我假设如果重定向不是
; 使用时，相应的文件句柄将为-1。
;
; 文件stdin应该是仅使用O rdu打开的文件。
; 文件stdout应该是仅使用O_wr打开的文件。
; 文件stdout应该是仅使用O_wr打开的文件。
;
; 小心使用为读写同时打开的文件描述符
; 并且使用相同的文件描述符——它可能不会做您想做的事情
; 希望它能做到。
;
; 另外请注意，您还可以使用pipe（）系统中的文件描述符
; 调用（以允许在命令之间进行管道连接）或网络插座，或
; 可以从文件描述符读取/写入的任何内容。
;---------------------------------------------------------------------*/
pid_t儿童；
child=fork（）；
if（子级<0）
报告错误（错误号）；
else if（子项>0）
{
智力状态；
int rc；
/*------------------------------------------------------------------
；等待子进程。需要向中添加更多代码
；描述符错误等等，但这只是一个练习
；读者
;-----------------------------------------------------------------*/
rc=等待（&状态）；
}
其他的
{
/*--------------------------------------------------------------------
；子进程。如果需要，设置重定向。一旦重新重定向
；已设置（使用dup2（）），原始文件描述符已关闭
；因为它不再需要，只会浪费数据库中的文件描述符
；子进程。
;-------------------------------------------------------------------*/
如果（文件标准>-1）
{
dup2（文件标准，标准文件编号）；
关闭（文件\u stdin）；
}
如果（文件\u stdout>-1）
{
dup2（文件标准，标准文件编号）；
关闭（文件存储）；
}
如果（文件\u stderr>-1）
{
dup2（文件号、文件号）；
关闭（文件存储）；
}
/*------------------------------------------------------------------
；在此处关闭所有不需要的打开文件。。。
;------------------------------------------------------------------*/
/*------------------------------------------------------------------
；需要用适当的值替换程序、ARGV和ENVP
;------------------------------------------------------------------*/
if（execve（程序、ARGV、环境）<0）
_退出（退出失败）；
}

---

显然，上面的代码需要根据您的项目进行调整，但这是一般流程

您在哪个平台上编程？是否打印过“find<！！！！”？请给出一个程序执行的示例。find<！！！！printedIs“michaelguan326>”是由您的程序打印的还是OS X命令行提示符？我尝试按照您的建议执行，但没有任何更改。输出相同。

for(i=0;i<n;i++){
        //printf("extracted token is %s\n",tokens[i]);
        char *ex = "exit";
        char *his = "history";

        if(strcmp(tokens[0],his) == 0 && max_cmd == 0 ){ //get history
            for(j=0;j<counter;j++){
                printf("%i. %s\n",j+1,historic_cmd[j]);         
            }

        }else if(strcmp(tokens[0], his) ==0 && max_cmd == 1){
            for(j=0; j<CMD_MAX;j++){
                printf("%i. %s\n",j+1,historic_cmd[j]);
            }
        }else if(strcmp(tokens[0],ex) == 0){ //exit program
            exit(2);
        }else{                      //forking
            pid = fork();
            if(pid){
                pid=wait(NULL);

                if(infile > 0)
                    dup2(fileno(fd),0);

                if(outfile > 0)
                    dup2(fileno(fd),1);

            }else{
                if(execvp(tokens[0],tokens)){
                    puts(strerror(errno));
                    exit(127);
                }

            }

        }




    } // end of for loop



}//end of while loop for user input

ps > s

user$>ps > s
ps: illegal option -- >
usage: ps [-AaCcEefhjlMmrSTvwXx] [-O fmt | -o fmt] [-G gid[,gid...]]
      [-u]
      [-p pid[,pid...]] [-t tty[,tty...]] [-U user[,user...]]
   ps [-L]
ps: illegal option -- >
usage: ps [-AaCcEefhjlMmrSTvwXx] [-O fmt | -o fmt] [-G gid[,gid...]]
      [-u]
      [-p pid[,pid...]] [-t tty[,tty...]] [-U user[,user...]]
   ps [-L]
ps: illegal option -- >
usage: ps [-AaCcEefhjlMmrSTvwXx] [-O fmt | -o fmt] [-G gid[,gid...]]
      [-u]
      [-p pid[,pid...]] [-t tty[,tty...]] [-U user[,user...]]
   ps [-L]
found > !!!!!----------------------------------------------------

int file_stdin;
int file_stdout;
int file_stderr;

/*--------------------------------------------------------------------
; code to set infile and outfile I'll assume that if redirection isn't
; being used, the appropriate filehandle will be -1.
;
; file_stdin  should be a file that is opened using O_RDONLY.
; file_stdout should be a file that is opened using O_WRONLY.
; file_stdout should be a file that is opened using O_WRONLY.
;
; Be wary of using a file descriptor opened for both reading and writing
; and using the same file descriptor---it will probably not do what you
; expect it to do.
;
; Also note, you can also use file descriptors from the pipe() system
; call (to allow piping from command to command) or network sockets, or
; anything that can be read/written from a file descriptor.
;---------------------------------------------------------------------*/

pid_t child;

child = fork();
if (child < 0)
  report_error(errno);
else if (child > 0)
{
  int status;
  int rc;

  /*------------------------------------------------------------------
  ; wait for the child process.  More code needs to be added to
  ; descriptor errors and what not, but that's left as an exercise for
  ; the reader
  ;-----------------------------------------------------------------*/

  rc = wait(&status);
}
else
{
  /*--------------------------------------------------------------------
  ; child process.  Set up redirection if required.  Once the rediretion
  ; has been set (using dup2()), the original file descriptor is closed   
  ; as it is no longer needed and just wastes file descriptors in the   
  ; child process.
  ;-------------------------------------------------------------------*/

  if (file_stdin > -1)
  {
    dup2(file_stdin,STDIN_FILENO);
    close(file_stdin);
  }

  if (file_stdout > -1)
  {
    dup2(file_stdout,STDOUT_FILENO);
    close(file_stdout);
  }

  if (file_stderr > -1)
  {
    dup2(file_stderr,STDERR_FILENO);
    close(file_stderr);
  }

  /*------------------------------------------------------------------
  ; close any unneeded open files here ... 
  ;------------------------------------------------------------------*/

  /*------------------------------------------------------------------
  ; PROGRAM, ARGV and ENVP need to be replaced with appropriate values
  ;------------------------------------------------------------------*/

  if(execve(PROGRAM,ARGV,ENVP) < 0)
    _exit(EXIT_FAILURE);
}