Invoke-Expression
will return all the text of the command being invoked.
But how can I get the system return value of whether this command has been executed successfully or with a failure? In CMD I could use %errorlevel%
to get external command execution state. What about PowerShell?
Normally you would use $?
to inspect the status of the last statement executed:
PS C:\> Write-Output 123 | Out-Null; $?
True
PS C:\> Non-ExistingCmdlet 123 | Out-Null; $?
False
However, this won't work with Invoke-Expression
, because even though a statement inside the expression passed to Invoke-Expression
may fail, the Invoke-Expression
call it self will have succeeded (ie. the expression, although invalid/non-functional was invoked none the less)
With Invoke-Expression
you'll have to use try:
try {
Invoke-Expression "Do-ErrorProneAction -Parameter $argument"
} catch {
# error handling go here, $_ contains the error record
}
or a trap:
trap {
# error handling goes here, $_ contains the error record
}
Invoke-Expression "More-ErrorProneActions"
The alternative is the append ";$?"
to the expression you want to invoke:
$Expr = "Write-Host $SomeValue"
$Expr += ';$?'
$Success = Invoke-Expression $Expr
if(-not $Success){
# seems to have failed
}
but relies on there not being any pipeline output
If the executable called by Invoke-Expression
supports it, you can use $LASTEXITCODE
. You have to be careful about variable scoping, though.
function foo
{
$global:LASTEXITCODE = 0 # Note the global prefix.
Invoke-Expression "dotnet build xyz" # xyz is meaningless, to force nonzero exit code.
Write-Host $LASTEXITCODE
}
foo
If you run it, the output will be:
Microsoft (R) Build Engine version 15.9.20+g88f5fadfbe for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.
MSBUILD : error MSB1009: Project file does not exist.
Switch: xyz
1
Observe the 1 at the end denoting nonzero exit code.
If you would forget the global:
prefix, instead the output would have 0. I believe this is because your function-scoped definition of LASTEXITCODE
would hide the globally-set one.
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