在C Shell中将stderr重定向到stdout [英] Redirect stderr to stdout in C shell
问题描述
当我在 csh 中运行以下命令时，我什么也没得到，但在 bash 中有效。
csh 中是否可以将标准错误重定向到标准输出？
When I run the following command in csh, I got nothing, but it works in bash.
Is there any equivalent in csh which can redirect the standard error to standard out?
somecommand 2>&1
推荐答案
csh Shell从未以其在重定向过程中操纵文件句柄的广泛能力而闻名。
The csh shell has never been known for its extensive ability to manipulate file handles in the redirection process.
您可以使用以下命令将标准输出和错误重定向到文件：
You can redirect both standard output and error to a file with:
xxx >& filename
但这不是您想要的，将标准错误重定向到 current 标准输出。
but that's not quite what you were after, redirecting standard error to the current standard output.
但是，如果基础操作系统在文件系统中公开了进程的标准输出（就像Linux在 / dev / stdout 中所做的那样，您可以按如下方式使用该方法：
However, if your underlying operating system exposes the standard output of a process in the file system (as Linux does with /dev/stdout), you can use that method as follows:
xxx >& /dev/stdout
这将同时强制标准输出和标准错误转到与当前标准输出相同的位置，有效地使用 bash 重定向， 2>& 1 。
This will force both standard output and standard error to go to the same place as the current standard output, effectively what you have with the bash redirection, 2>&1.
请记住，这不是 csh 功能。如果您运行的操作系统不会将标准输出显示为文件，则不能使用此方法。
Just keep in mind this isn't a csh feature. If you run on an operating system that doesn't expose standard output as a file, you can't use this method.
但是，还有另一种方法。如果使用 |& 发送到管道，则可以将两个流合并为一个，那么您要做的就是找到管道将其标准输入写入其标准输出的组件。如果您不知道这样的事情， cat 就是这样，如果您不给它任何参数的话。因此，您可以在以下特定案例中实现目标：
However, there is another method. You can combine the two streams into one if you send it to a pipeline with |&, then all you need to do is find a pipeline component that writes its standard input to its standard output. In case you're unaware of such a thing, that's exactly what cat does if you don't give it any arguments. Hence, you can achieve your ends in this specific case with:
xxx |& cat
当然，也没有什么可以阻止您运行 bash （假设它在系统上的某个位置） 内 code>脚本为您提供增加的功能。然后，对于更复杂的 csh 可能难以解决的情况，您可以使用该shell的丰富重定向。
Of course, there's also nothing stopping you from running bash (assuming it's on the system somewhere) within a csh script to give you the added capabilities. Then you can use the rich redirections of that shell for the more complex cases where csh may struggle.
让我们探索一下这更详细。首先，创建一个可执行文件 echo_err ，它将向 stderr 中写入一个字符串：
Let's explore this in more detail. First, create an executable echo_err that will write a string to stderr:
#include <stdio.h>
int main (int argc, char *argv[]) {
fprintf (stderr, "stderr (%s)\n", (argc > 1) ? argv[1] : "?");
return 0;
}
然后使用控制脚本 test.csh 会显示它的作用：
Then a control script test.csh which will show it in action:
#!/usr/bin/csh
ps -ef ; echo ; echo $$ ; echo
echo 'stdout (csh)'
./echo_err csh
bash -c "( echo 'stdout (bash)' ; ./echo_err bash ) 2>&1"
echo PID和 ps 的用法很简单，因此您可以确保运行此脚本的 csh 。当您使用以下命令运行此脚本时：
The echo of the PID and ps are simply so you can ensure it's csh running this script. When you run this script with:
./test.csh >test.out 2>test.err
（初始重定向由 bash 设置 csh 开始运行脚本之前），并检查 out / err 文件，您会看到：
(the initial redirection is set up by bash before csh starts running the script), and examine the out/err files, you see:
test.out:
UID PID PPID TTY STIME COMMAND
pax 5708 5364 cons0 11:31:14 /usr/bin/ps
pax 5364 7364 cons0 11:31:13 /usr/bin/tcsh
pax 7364 1 cons0 10:44:30 /usr/bin/bash
5364
stdout (csh)
stdout (bash)
stderr (bash)
test.err:
stderr (csh)
您可以看到 test.csh 进程是在C shell中运行，从那里调用 bash 可以为您提供完整的 bash 重定向的力量。
You can see there that the test.csh process is running in the C shell, and that calling bash from within there gives you the full bash power of redirection.
2>&a mp; 1 在 bash 命令中，可以很容易地将标准错误重定向到 current 标准输出（根据需要）无需事先知道标准输出的当前位置。
The 2>&1 in the bash command quite easily lets you redirect standard error to the current standard output (as desired) without prior knowledge of where standard output is currently going.
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