$LastExitCode=0, but $?= False in PowerShell. Redirecting stderr to stdout gives NativeCommandError

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problem ：

Why does PowerShell show the surprising behaviour in the second example below? Why? PowerShell The second example below shows surprising behavior ？

First, an example of sane behaviour: First , An example of rational behavior ：

PS C:\> & cmd /c "echo Hello from standard error 1>&2"; echo "`$LastExitCode=$LastExitCode and `$?=$?"Hello from standard error$LastExitCode=0 and $?=True

No surprises. No surprises .I print a message to standard error (using cmd 's echo ). I print messages to standard errors （ Use cmd Of echo ）.I inspect the variables $? I check the variables $?and $LastExitCode . and $LastExitCode .They equal to True and 0 respectively, as expected. As expected , They are equal to respectively True and 0.

However, if I ask PowerShell to redirect standard error to standard output over the first command, I get a NativeCommandError: however , If I ask PowerShell Redirect standard errors to standard output with the first command , I will receive NativeCommandError：

PS C:\> & cmd /c "echo Hello from standard error 1>&2" 2>&1; echo "`$LastExitCode=$LastExitCode and `$?=$?"cmd.exe : Hello from standard errorAt line:1 char:4+ cmd <<<<  /c "echo Hello from standard error 1>&2" 2>&1; echo "`$LastExitCode=$LastExitCode and `$?=$?"    + CategoryInfo          : NotSpecified: (Hello from standard error :String) [], RemoteException    + FullyQualifiedErrorId : NativeCommandError$LastExitCode=0 and $?=False

My first question, why the NativeCommandError? My first question , Why NativeCommandError？

Secondly, why is $? secondly , Why $?False when cmd ran successfully and $LastExitCode is 0? When cmd Run successfully and $LastExitCode by 0 When is False？PowerShell's documentation about automatic variables doesn't explicitly define $?PowerShell About automatic variables The documentation for is not clearly defined $?..I always supposed it is True if and only if $LastExitCode is 0, but my example contradicts that. If and only if $LastExitCode by 0 when , I always thought it was True, But my example contradicts this .

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Here's how I came across this behaviour in the real-world (simplified). This is how I encounter this behavior in the real world （ simplify ）.It really is FUBAR. It's really FUBAR.I was calling one PowerShell script from another. I am calling one from another PowerShell Script .The inner script: Internal script ：

cmd /c "echo Hello from standard error 1>&2"if (! $?){    echo "Job failed. Sending email.."    exit 1}# Do something else

Running this simply as .\\job.ps1 , it works fine, and no email is sent. Simply regard it as .\\job.ps1 function , It works , And don't send email .However, I was calling it from another PowerShell script, logging to a file .\\job.ps1 2>&1 > log.txt . however , I am from another PowerShell Script calls it , Record to file .\\job.ps1 2>&1 > log.txt .In this case, an email is sent! under these circumstances , Will send an email ！What you do outside the script with the error stream affects the internal behaviour of the script. What you do outside the script using the error flow affects the internal behavior of the script .Observing a phenomenon changes the outcome. Observation will change the result .This feels like quantum physics rather than scripting! It feels like quantum physics, not a script ！

[Interestingly: .\\job.ps1 2>&1 may or not blow up depending on where you run it][ Interestingly ： .\\job.ps1 2>&1 May or may not explode , It depends on where you run it ]

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Solution ：

Reference resources ： https://stackoom.com/en/question/ikjt