使用 bash，如何将标准错误传送到另一个进程？
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With bash, how can I pipe standard error into another process?
提问by paxdiablo
It's well known how to pipe the standard ouput of a process into another processes standard input:
众所周知，如何将一个进程的标准输出通过管道传输到另一个进程的标准输入中：
proc1 | proc2
But what if I want to send the standard error of proc1 to proc2 and leave the standard output going to its current location? You would think bashwould have a command along the lines of:
但是，如果我想将 proc1 的标准错误发送到 proc2 并将标准输出留在其当前位置怎么办？你会认为bash会有一个类似的命令：
proc1 2| proc2
But, alas, no. Is there any way to do this?
但是，唉，没有。有没有办法做到这一点？
回答by Scot
There is also process substitution. Which makes a process substitute for a file.
You can send stderrto a file as follows:
还有过程替换。这使得一个进程替代了一个文件。
您可以stderr按如下方式发送到文件：
process1 2> file
But you can substitute a process for the file as follows:
但是您可以按如下方式替换文件的进程：
process1 2> >(process2)
Here is a concrete example that sends stderrto both the screen and appends to a logfile
这是一个发送stderr到屏幕并附加到日志文件的具体示例
sh myscript 2> >(tee -a errlog)
回答by paxdiablo
You can use the following trick to swapstdoutand stderr. Then you just use the regular pipe functionality.
您可以使用以下技巧来交换stdout和stderr。然后您只需使用常规管道功能。
( proc1 3>&1 1>&2- 2>&3- ) | proc2
Provided stdoutand stderrboth pointed to the same place at the start, this will give you what you need.
提供stdout并且stderr两者在开始时都指向同一个地方，这将为您提供所需的东西。
What the x>ybit does is to change file handle xso it now sends its information to where file handle ycurrently points. For our specific case:
该x>y位的作用是更改文件句柄，x以便它现在将其信息发送到文件句柄y当前指向的位置。对于我们的具体情况：
3>&1creates a newhandle3which will output to the currenthandle1(original stdout), just to save it somewhere for the final bullet point below.1>&2modifies handle1(stdout) to output to the currenthandle2(original stderr).2>&3-modifies handle2(stderr) to output to the currenthandle3(original stdout) then closes handle3(via the-at the end).
3>&1创建一个将输出到当前句柄（原始标准输出）的新句柄，只是为了将其保存在某处以用于下面的最后一个要点。311>&2修改句柄1(stdout) 以输出到当前句柄2（原始 stderr）。2>&3-修改句柄2（stderr）以输出到当前句柄3（原始标准输出）然后关闭句柄3（通过-最后）。
It's effectively the swap command you see in sorting algorithms:
它实际上是您在排序算法中看到的交换命令：
temp = value1;
value1 = value2;
value2 = temp;
回答by Paused until further notice.
Bash 4 has this feature:
Bash 4 有这个功能：
If `|&' is used, the standard error of command1 is connected to command2's standard input through the pipe; it is shorthand for 2>&1 |. This implicit redirection of the standard error is performed after any redirections specified by the command.
如果使用`|&'，则command1的标准错误通过管道连接到command2的标准输入；它是 2>&1 | 的简写。标准错误的这种隐式重定向在命令指定的任何重定向之后执行。
zsh also has this feature.
zsh 也有这个功能。
--
——
With other/older shells, just enter this explicitly as
对于其他/较旧的外壳，只需明确输入
FirstCommand 2>&1 | OtherCommand
第一个命令 2>&1 | 其他命令
回答by kccqzy
Swapping is great as it solves the problem. Just in case you do not even need the original stdout, you can do it this way:
交换很棒，因为它解决了问题。以防万一您甚至不需要原始标准输出，您可以这样做：
proc1 2>&1 1>/dev/null | proc2
The order is vital; you would not want:
秩序至关重要；你不会想要：
proc1 >/dev/null 2>&1 | proc1
As this will redirect everything to /dev/null!
因为这会将所有内容重定向到/dev/null!
回答by sbingner
None of these really worked very well. The best way I found do do what you wanted is:
这些都没有真正奏效。我发现做你想做的最好的方法是：
(command < input > output) 2>&1 | less
This only works for cases where commanddoes not need keyboard input. eg:
这仅适用于command不需要键盘输入的情况。例如：
(gzip -d < file.gz > file) 2>&1 | less
would put gzip errors into less
会将 gzip 错误放入 less
