如何捕获由system()启动的过程的标准输出 [英] How to capture standard output of the process started by system()

问题描述

如何将system("openssl enc -aes-128-cbc -k secret -P -md sha1 > FILENAME")的输出保存到文件中.

How do I save the output of system("openssl enc -aes-128-cbc -k secret -P -md sha1 > FILENAME") into a file.

我尝试了以下操作:

NSArray *paths = NSSearchPathForDirectoriesInDomains

(NSDocumentDirectory, NSUserDomainMask, YES);

NSString *documentsDirectory = [paths objectAtIndex:0];

NSString *fileName = [NSString stringWithFormat:@"%@/textfile.txt",

                      documentsDirectory];

NSString *str=[NSString stringWithFormat:@"openssl enc -aes-128-cbc -k secret -P -md sha1 > %s",[fileName UTF8String]];
NSLog(@"AES Key is %@",str);
system([str UTF8String]);

NSString *strAES = [NSString stringWithContentsOfFile:fileName encoding:nil error:nil];
NSLog(@"strAES Key is %@",strAES);

NSString *strAESKey=[[[[strAES componentsSeparatedByString:@"\n"] objectAtIndex:1] componentsSeparatedByString:@"="] objectAtIndex:1];
NSLog(@"strAESKey Key is %@",strAESKey);

// NSString *content = @"One\nTwo\nThree\nFour\nFive";
  [str writeToFile:fileName atomically:NO encoding:NSStringEncodingConversionAllowLossy error:nil];`

我要去哪里错了?

system()函数将输出发送到控制台，但是由于iPhone没有控制台，因此我需要将输出重定向到文本文件，并从文件中获取密钥，以将其用于加密/解密. /p>

The system() function sends the output to the console but since the iPhone does not have a console, I need to redirect the output to a text file and get the key from the file to use it for encryption/decryption.

推荐答案

首先:请注意，我认为您不能在没有越狱的iOS上使用system(3).但是我不确定，所以我将解释如何做:

First of all: be aware, I don't think you can use system(3) on an not jail broken iOS. But I'm not sure, so I will explain how to do it:

这有点棘手.

要实现它，您必须知道每个进程都使用三个文件描述符打开:一个用于读取(stdin用于标准输入)和两个用于写入(stdout用于标准输出，stderr用于标准错误)输出).它们的fd编号分别为0(stdin)，1(stdout)和2(stderr).

To achieve it, you have to know that each process gets opened with three file descriptors: one for reading (stdin for standard input) and two for writing (stdout for standard output and stderr for standard error output). They have the fd numbers 0 (stdin), 1 (stdout) and 2 (stderr).

要将标准输出或标准错误从程序重定向到文件，您必须执行以下操作:

To redirect standard output or standard error to a file from a program, you have to do the following:

• 首先，fork(2)该过程.在父进程中，子进程waitpid(2)会ze头.
• 在子进程中:
  • 重新打开(freopen(3))stdout和stderr到要重定向输出的文件.
  • 使用execve(2)执行要调用的程序
  • 命令终止时，父级将获得SIGCHLD，并且waitpid(2)应该返回
  • first, fork(2) the process. In the parent process waitpid(2) for the child prozess.
  • In the child process:
    • reopen (freopen(3)) stdout and stderr to the file you want the output to be redirected.
    • use execve(2) to execute the program you want to call
    • when the command terminates, the parent gets a SIGCHLD and waitpid(2) should return

    括号中的数字描述了该功能的手册页中的章节(例如，man 2 waitpid).

    The number in the brackets describes the chapter in the man pages (man 2 waitpid, e.g.) for the function.

    希望这会有所帮助，如果您还有其他问题，请询问:-)

    Hope this helps, if you have more questions, ask :-)

    更新:由于OP只是想获取输出，而不是专门获取文件，因此可以使用popen(3):

    Update: Since the OP just wants to get the output and not specificly into a file, you can use popen(3):

    int status;
    char value[1024];
    FILE *fp = popen("openssl enc -aes-128-cbc -k secret -P -md sha1", "r");
    
    if (fp == NULL) exit(1); // handle error
    
    while (fgets(value, 1024, fp) != NULL) {
      printf("Value: %s", value);
    }
    
    status = pclose(fp);
    if (status == -1) {
      /* Error reported by pclose() */
    }
    else {
      /* Use macros described under wait() to inspect `status' in order
       to determine success/failure of command executed by popen() */
    }
    

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