CMD管道与Powershell管道不同? [英] CMD pipe different form Powershell pipe?
问题描述
我正在尝试将 Node.js 输出通过管道传输到 preatty-pino
node .distGameNode.js |pino-漂亮
在 CMD 中运行它我得到了我的格式化输出但是在 powershell 中运行它我什么也得不到.我读到 Powershell 在管道时使用对象,所以我尝试了
node .distGameNode.js |外串-Stream |pino-漂亮
但这也行不通.
为什么它在 CMD 中有效,而在 Powershell 中无效?谢谢:)
注意:问题中描述的特定pino-pretty
问题未通过以下信息解决.Lukas(OP)已在
注意
DecodedOutput
属性,显示基于解释 Python 输出的 mis 解码结果作为 OEM- 而不是作为 ANSI 编码:'eΘ'
.(Input*
属性为空,因为该命令不涉及管道数据到 Python 脚本.)相比之下,直接显示打印输出打印很好(因为 Python 那时 - 并且只有那时 - 使用 Unicode),隐藏问题,但是一旦您想以编程方式处理输出 - 在变量中捕获,发送到管道中的另一个命令,重定向到文件 - 编码问题就会浮出水面.
和
Invoke-WithEncoding
一样,Debug-NativeInOutput
支持-Encoding
参数,所以如果你传递-EncodingAnsi
到上面的调用,你会看到 Python 的输出被正确解码.输出反映了这样一个事实:在 PowerShell (Core) 中,
$OutputEncoding
默认为 UTF-8,而在 Windows PowerShell 中,它默认为 ASCII(!).这种与控制台窗口中实际编码的不匹配是有问题的,这条评论在 GitHub 问题 #14945 上提出了一种将来解决此问题的方法(仅适用于 PowerShell(核心)).
I am trying to pipe Node.js output to preatty-pino
node .distGameNode.js | pino-pretty
running this in the CMD I get my formated output but running it inside a powershell I get nothing. I read that Powershell is using objects when piping, so I tried
node .distGameNode.js | Out-String -Stream | pino-pretty
But this also does not work.
Why does it work inside CMD but not inside Powershell ? Thanks :)
Note: The specific pino-pretty
problem described in the question is not resolved by the information below. Lukas (the OP) has filed a bug report here.
It's surprising that you get nothing, but the fundamental difference is:
cmd.exe
's pipeline conducts raw data, i.e. byte streams (which a given program receiving the data may or may not itself interpret as text).PowerShell's pipeline, when talking to external programs, conducts only text (strings), which has two implications:
On piping data to an external program, text must be encoded, which happens based on the character encoding stored in preference variable
$OutputEncoding
.On receiving data from an external program, data must be decoded, which happens based on the character encoding stored in
[Console]::OutputEncoding
, which by default is the system's OEM code page, as reflected inchcp
.This decoding happens invariably, irrespective of whether the data is then further processed in PowerShell or passed on to another external program.
- This sometimes problematic lack of ability to send raw data through PowerShell's pipeline even between two external programs is discussed in this answer.
The only exception is if external-program output is neither captured, sent on through the pipeline, nor redirected to a file: in that case, the data prints straight to the console (terminal), but only in a local console (when using PowerShell remoting to interact with a remote machine, decoding is again invariably involved).
- This direct-to-display printing can sometimes hide encoding problems, because some programs, notably
python
, use full Unicode support situationally in that case; that is, the output may print fine, but when you try to process it further, encoding problems can surface. - A simple way to force decoding is to enclose the call in
(...)
; e.g.,
python -c "print('eé')"
prints fine, but
(python -c "print('eé'))"
surfaces an encoding problem; see the bottom section for more information
- This direct-to-display printing can sometimes hide encoding problems, because some programs, notably
While console applications traditionally use the active OEM code page for character encoding and decoding, Node.js always uses UTF-8.
Therefore, in order for PowerShell to communicate properly with Node.js programs, you must (temporarily) set the following first:
$OutputEncoding = [Console]::OutputEncoding = [System.Text.UTF8Encoding]::new()
If you want to fundamentally switch to UTF-8, either system-wide (which has far-reaching consequences) or only for PowerShell console windows, see this answer.
As an aside: an intermediate Out-String -Stream
pipeline segment is never needed for relaying an external program's output - it is effectively (a costly) no-op, because streaming stdout output line by line is what PowerShell does by default. In other words: it is not surprising that it made no difference in your case.
Optional reading: Convenience function Invoke-WithEncoding
and diagnostic function Debug-NativeInOutput
for ad-hoc encoding needs / diagnosis:
If switching all PowerShell consoles to UTF-8 isn't an option and/or you need to deal with "rogue" programs that use a specific encoding other than UTF-8 or the active OEM code page, you can install:
- Function
Invoke-WithEncoding
, which temporarily switches to a given encoding when invoking an external program, directly from this Gist as follows (I can assure you that doing so is safe, but you should always check):
# Download and define advanced function Invoke-WithEncoding in the current session.
irm https://gist.github.com/mklement0/ef57aea441ea8bd43387a7d7edfc6c19/raw/Invoke-WithEncoding.ps1 | iex
- Function
Debug-NativeInOutput
, which helps diagnose encoding problems with external programs, directly from this Gist as follows (again, you should check first):
# Download and define advanced function Debug-NativeInOutput in the current session.
irm https://gist.github.com/mklement0/eac1f18fbe0fc2798b214229b747e5dd/raw/Debug-NativeInOutput.ps1 | iex
Below are example commands that use a python
command to print an accented character.
Like Node.js, Python's behavior is nonstandard, although it doesn't use UTF-8, but the system's active ANSI(!) code page (rather than the expected OEM code page).
That is, even if you switch your PowerShell consoles UTF-8, communication with Python scripts won't work properly by default, unless extra effort is made, which Invoke-WithEncoding
can encapsulate for you:
Note: I'm using Python as an example here, to illustrate how the functions work. It is possible to make Python use UTF-8, namely by either setting environment variable PYTHONUTF8
to 1
or - in v3.7+ - by passing parameter -X utf8
(case-exactly).
Invoke-WithEncoding
example:
# Outputs *already-decoded* output, so if the output *prints* fine,
# then *decoding* worked fine too.
PS> Invoke-WithEncoding { python -c "print('eé')" } -Encoding Ansi -WindowsOnly
eé
Note that
Invoke-WithEncoding
ensures that actual decoding to a .NET string happens before it outputs, so that encoding problems aren't accidentally masked by the direct-to-display output seemingly being correct on Windows (see below for more).-WindowsOnly
is for cross-platform compatibility and ensures that the encoding is only applied on Windows in this case (on Unix, Python uses UTF-8).
Debug-NativeInOutput
example:
With the PowerShell console at its default, using the system's OEM code page, you'll see the following output with the same Python command, calling from PowerShell (Core) 7.1:
PS> Debug-NativeInOutput { python -c "print('eé')" }
Note the
DecodedOutput
property, showing the mis-decoded result based on interpreting Python's output as OEM- rather than as ANSI-encoded:'eΘ'
. (TheInput*
properties are blank, because the command did not involve piping data to the Python script.)By contrast, with direct-to-display printing the output prints fine (because Python then - and only then - uses Unicode), which hides the problem, but as soon you want to programmatically process the output - capture in a variable, send to another command in the pipeline, redirect to a file - the encoding problem will surface.
Like
Invoke-WithEncoding
,Debug-NativeInOutput
supports an-Encoding
parameter, so if you pass-Encoding Ansi
to the call above, you'll see that Python's output is decoded properly.The output reflects the fact that, in PowerShell (Core),
$OutputEncoding
defaults to UTF-8, whereas in Windows PowerShell it defaults to ASCII(!). This mismatch with the actual encoding in effect in the console window is problematic, and this comment on GitHub issue #14945 proposes a way to resolve this (for PowerShell (Core) only) in the future.
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