重定向不起作用 [英] Redirection Doesn't Work

问题描述

我想将程序的输出放入文件中.我输入了以下内容:

I want to put my program's output into a file. I keyed in the following :

./prog > log 2>&1

但是文件日志" 中没有任何内容.我正在使用Ubuntu 11.10，默认外壳为bash.

But there is nothing in the file "log". I am using the Ubuntu 11.10 and the default shell is bash.

任何人都知道造成这种情况的原因以及如何调试它?

Anybody know the cause of this AND how I can debug this?

推荐答案

有很多可能的原因:

• 当您尝试通过截断重定向到文件时，程序会从log文件读取输入(请参阅)
• 对输出进行缓冲，以便在刷新输出缓冲区之前，您不会在文件中看到数据.如果使用C ++ I/O流等，则可以手动调用fflush或输出std::flush.
• 程序足够聪明，如果输出流不是终端，则禁用输出.
• 您查看了错误的文件(即在另一个目录中).
• 您尝试错误地转储文件内容.
• 您的程序将第一个字符输出为'\ 0'，因此即使有一些数据，输出也似乎为空.
• 命名自己的名字.

• The program reads the input from log file while you try to redirect into it with truncation (see Why doesn't "sort file1 > file1" work?)
• The output is buffered so that you don't see data in the file until the output buffer is flushed. You can manually call fflush or output std::flush if using C++ I/O stream etc.
• The program is smart enough and disables output if the output stream is not a terminal.
• You look at the wrong file (i.e. in another directory).
• You try to dump file's contents incorrectly.
• Your program outputs '\0' as the first character so the output appears to be empty, even though there is some data.
• Name your own.

您最好的选择是在调试器(如gdb)下运行此应用程序，或使用strace或ptrace(或两者)查看程序在做什么.我的意思是，实际上，输出重定向在过去的40年中一直有效，因此问题一定存在于其他地方.

Your best bet is to run this application under a debugger (like gdb) or use strace or ptrace (or both) and see what the program is doing. I mean, really, output redirection works for the last like 40 years, so the problem must be somewhere else.

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