stderr | 易学教程

Why is my machine writing stderr into stdout?

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问题 While writing code against the System.Diagnostics.Process tools in C#, I was catching only StandardOutput and parsing it. However, a unit test around this failed on the build server. After a colleague tried on his machine, it failed as well. Then I found Jon Skeet's answer to a question about why StandardOutput was empty, and he mentioned capturing both StandardOutput and StandardError from System.Diagnostics.Process. Sure enough, we tried that on my colleague's machine and it worked. My

python: fork without an external command, and capturing stdout and stderr separately

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问题 I'd like to fork a subprocess in python that does not run an external command ... it would just run a defined function. And I want to capture stdout and stderr separately. I know how to use os.fork() and os.pipe() , but that mechanism only gives me two fd's to work with. I'm looking for three fd's: one for stdin , one for stdout , and one for stderr . This is easy to manage using subprocess.Popen when running an external command, but that function doesn't seem to allow a local function to be

Bash eating stderr output

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问题 I'm calling a command line tool we wrote from bash on OS X and I have the problem that I don't get the stderr output but only printf's written to stdout. That's my call: echo "someInputString" |theTool -v someArg I also tried: echo "someInputString" |theTool -v someArg 2>&1 without success... I bet it's trivial but I don't know what needs to be done. Thanks in advance! 回答1: Redirect the stderr stream output with 2> . echo "someInputString" |theTool -v someArg 2> error_file 来源： https:/

socket网络编程-粘包

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1.什么是粘包只要tcp有粘包现象，udp不会粘包粘包主要问题是接收方不知道消息之间的界限，不知道一次性提取多少字节的数据而造成的 tcp和dup的区别 1.tcp是基于数据流的，收发的消息不能为空，这酒需要在客户端和服务端都添加空消息的处理机制，防止程序卡主 2.udp是基于数据报，输入发送空内容（直接回车），那也不是空消息，udp协议会帮你封装一个消息头（消息来源地址，端口等信息）即面向消息的通信是有消息保护边界的。为什么出现粘包 tcp的协议数据不会丢失，是因为没有收完的数据会在基于上次继续接受，已端总是在收到ack时才清楚缓冲区内容，所以数据是可靠，但会出现粘包现象 udp的recvfrom是阻塞的，一个recvfrom（x）必须对应一个sendinto（y），收完x个字节是数据就算完成，若是y>x那就意味着数据丢失，这意味着udp不会出现粘包，但是数据会丢失，不可靠 3.tcp（传输控制协议）为什么可靠？ tcp是面向连接，面向数据流，提供可靠性服务 tcp传输数据时候先把数据传输到自己缓存，然后通过协议控制将缓存中数据发往对端，对端返回一个ack=1，发送端则清理缓存中数据对端返回一个ack=0，则重新发送，所以tcp可靠 2.udp（用户数据报协议）为什么不可靠？ udp.是面向无连接的，面向消息流，提供高效率服务只管把数据发送给对端，不管对端是否收到

Paramiko recv()/read()/readline(s)() on stderr returns empty string

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问题 I'm using paramiko to collect some information on a remote host and experience issues, when reading ( read() / readline() / readlines() ) from the stderr channel. Sometimes stderr.read() returns an empty string which to me looks like a result of a race condition. However, according to documentation and examples I found on the internet, this seems the exact way to go. I also tried to open a dedicated channel and make use of chan.recv_ready() / chan.recv_stderr_ready() and reading from

Catch stderr in subprocess.check_call without using subprocess.PIPE

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问题 I'd like to do the following: shell out to another executable from Python, using subprocess.check_call catch the stderr of the child process, if there is any add the stderr output to the CalledProcessError exception output from the parent process. In theory this is simple. The check_call function signature contains a kwarg for stderr : subprocess.check_call(args, *, stdin=None, stdout=None, stderr=None, shell=False) However, immediately below that the documentation contains the following

Cronjob - How to output stdout, and ignore stderr

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问题 Is it possible to output stdout to file, but ignore stderr ? I have a Python script that uses sys.stderr.write(error) to output errors to stderr . I'd like to ignore these for this particular script. How is this possible? Here is the current entry in the crontab: * * * * * /Users/me/bin/scrape-headlines /Users/me/proxies.txt >> /Users/me/headlines.txt 2>&1 scrape-headlines is a bash script that calls the Python script. 回答1: The 2>&1 redirects stderr to stdout , appending it to the headlines

网络编程（五）：粘包现象

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进击のpython 网络编程——粘包现象前面我们提到了套接字的使用方法，以及相关bug的排除还记得我们提到过一个1024吗？我们现在要针对这个来研究一下一个陷阱在研究这个陷阱之前我要先教你几条语句这是windows的命令啊 ipfonfig 查看本地网卡的ip地址 dir 查看某一个文件夹下的子文件名和子文件夹名 tasklist 查看运行的进程那我这三条命令怎么执行呢？？直接敲？？好像没什么用，所以说我需要打开我的cmd窗口来键入这些命令而cmd也就是一个能把特殊的字母组合执行出来的一个程序而已当我在cmd里键入dir的时候得到的就是这些东西那我想在编译器里搞这个东西呢？哦！第一反应就是os模块 import os os.system("dir") 就执行起来了吧那我这算是拿到结果了吗? 我觉得不算,为什么? 咱们想要达到的效果是我在客户端输入一个dir发送给服务端,服务端给我返回这一堆东西才叫拿到结果了是吧 import os res = os.system("dir") print(f"返回的结果是:{res}") 那结果我打印的是什么呢??是0!那为什么是这个呢? 这个0是代表这个命令是不是成功如果返回的是0,就是成功了,如果是非零,就是失败了! 所以说他返回的是一个是否成功执行语句的状态,而不是执行语句的返回结果那os模块就被pass掉了

Check for stdout or stderr

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问题 One of the binaries which I am using in my shell script is causing a segmentation fault (RETURN VALUE: 139) And even though, I am redirecting both stdout and stderr to a logfile, the Segmentation Fault error messages is displayed in the terminal when I am running the shell script. Is it possible to redirect this message from Segfault to a logfile ?? 回答1: The Segmentation Fault message you see is printed by the shell that is running your program. This behavior varies from shell to shell, so a

freopen not writing to the specified file

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问题 I am trying to redirect output of stdout and stderr using a file. I am using freopen and it creates the file in the correct directory but the file is blank. When I comment out the code to redirect the stdout and stderr - the output shows up on the console. Here is the code: freopen(stderrStr.c_str(), "a+", stderr); //where stderrStr and stdoutStr are the path/file name freopen(stdoutStr.c_str(), "a+", stdout); fclose(stdout); fclose(stderr); I have placed a printf("I WORK") in main and

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