PowerShell -is operator always matching PSCustomObject when used in ForEach-Object
Using PowerShell Core 6.1 on Mac. It appears that piping an array to ForEach-Object is modifying or wrapping each element such that the -is operator considers all of them to be PSCustomObjects.
Let me demonstrate:
Set up an array of four items of different types (use of JSON because that's where the data is coming from in my real use case):
$a = '[4, "Hi", {}, true]' | ConvertFrom-Json
Iterate the list by index and determine which ones are PSCustomObjects:
0..3 | ForEach-Object {
$v = $a[$_]
$t = $v.GetType().FullName
$is = $v -is [PSCustomObject]
"$t - $is"
}
The output (for me) is exactly what I would expect:
System.Int64 - False
System.String - False
System.Management.Automation.PSCustomObject - True
System.Boolean - False
But if I just pipe the array to ForEach-Object:
$a | ForEach-Object {
$v = $_
$t = $v.GetType().FullName
$is = $v -is [PSCustomObject]
"$t - $is"
}
Now the output claims that all four are PSCustomObjects:
System.Int64 - True
System.String - True
System.Management.Automation.PSCustomObject - True
System.Boolean - True
Could anyone explain what is happening here?
powershell powershell-v6.0
asked Nov 12 '18 at 18:55
user221592user221592
433
add a comment |
Using PowerShell Core 6.1 on Mac. It appears that piping an array to ForEach-Object is modifying or wrapping each element such that the -is operator considers all of them to be PSCustomObjects.
Let me demonstrate:
Set up an array of four items of different types (use of JSON because that's where the data is coming from in my real use case):
$a = '[4, "Hi", {}, true]' | ConvertFrom-Json
Iterate the list by index and determine which ones are PSCustomObjects:
0..3 | ForEach-Object {
$v = $a[$_]
$t = $v.GetType().FullName
$is = $v -is [PSCustomObject]
"$t - $is"
}
The output (for me) is exactly what I would expect:
System.Int64 - False
System.String - False
System.Management.Automation.PSCustomObject - True
System.Boolean - False
But if I just pipe the array to ForEach-Object:
$a | ForEach-Object {
$v = $_
$t = $v.GetType().FullName
$is = $v -is [PSCustomObject]
"$t - $is"
}
Now the output claims that all four are PSCustomObjects:
System.Int64 - True
System.String - True
System.Management.Automation.PSCustomObject - True
System.Boolean - True
Could anyone explain what is happening here?
powershell powershell-v6.0
asked Nov 12 '18 at 18:55
user221592user221592
433
1
[PSCustomObject]is an alias for[System.Management.Automation.PSObject], but not to[System.Management.Automation.PSCustomObject]. So, that means that all four are wrapped into[PSObject]insideForEach-Objectcmdlet. Likely becauseInputObjectparameter ofForEach-Objecttyped as[PSObject]andForEach-Objectdoes not do unwrapping.
– PetSerAl
Nov 12 '18 at 19:43
add a comment |
Using PowerShell Core 6.1 on Mac. It appears that piping an array to ForEach-Object is modifying or wrapping each element such that the -is operator considers all of them to be PSCustomObjects.
Let me demonstrate:
Set up an array of four items of different types (use of JSON because that's where the data is coming from in my real use case):
$a = '[4, "Hi", {}, true]' | ConvertFrom-Json
Iterate the list by index and determine which ones are PSCustomObjects:
0..3 | ForEach-Object {
$v = $a[$_]
$t = $v.GetType().FullName
$is = $v -is [PSCustomObject]
"$t - $is"
}
The output (for me) is exactly what I would expect:
System.Int64 - False
System.String - False
System.Management.Automation.PSCustomObject - True
System.Boolean - False
But if I just pipe the array to ForEach-Object:
$a | ForEach-Object {
$v = $_
$t = $v.GetType().FullName
$is = $v -is [PSCustomObject]
"$t - $is"
}
Now the output claims that all four are PSCustomObjects:
System.Int64 - True
System.String - True
System.Management.Automation.PSCustomObject - True
System.Boolean - True
Could anyone explain what is happening here?
powershell powershell-v6.0
asked Nov 12 '18 at 18:55
user221592user221592
433
Using PowerShell Core 6.1 on Mac. It appears that piping an array to ForEach-Object is modifying or wrapping each element such that the -is operator considers all of them to be PSCustomObjects.
Let me demonstrate:
Set up an array of four items of different types (use of JSON because that's where the data is coming from in my real use case):
$a = '[4, "Hi", {}, true]' | ConvertFrom-Json
Iterate the list by index and determine which ones are PSCustomObjects:
0..3 | ForEach-Object {
$v = $a[$_]
$t = $v.GetType().FullName
$is = $v -is [PSCustomObject]
"$t - $is"
}
The output (for me) is exactly what I would expect:
System.Int64 - False
System.String - False
System.Management.Automation.PSCustomObject - True
System.Boolean - False
But if I just pipe the array to ForEach-Object:
$a | ForEach-Object {
$v = $_
$t = $v.GetType().FullName
$is = $v -is [PSCustomObject]
"$t - $is"
}
Now the output claims that all four are PSCustomObjects:
System.Int64 - True
System.String - True
System.Management.Automation.PSCustomObject - True
System.Boolean - True
Could anyone explain what is happening here?
powershell powershell-v6.0
powershell powershell-v6.0
asked Nov 12 '18 at 18:55
user221592user221592
433
asked Nov 12 '18 at 18:55
user221592user221592
433
asked Nov 12 '18 at 18:55
user221592user221592
433
asked Nov 12 '18 at 18:55
user221592user221592
433
asked Nov 12 '18 at 18:55
user221592user221592
433
433
1
[PSCustomObject]is an alias for[System.Management.Automation.PSObject], but not to[System.Management.Automation.PSCustomObject]. So, that means that all four are wrapped into[PSObject]insideForEach-Objectcmdlet. Likely becauseInputObjectparameter ofForEach-Objecttyped as[PSObject]andForEach-Objectdoes not do unwrapping.
– PetSerAl
Nov 12 '18 at 19:43
add a comment |
1
[PSCustomObject]is an alias for[System.Management.Automation.PSObject], but not to[System.Management.Automation.PSCustomObject]. So, that means that all four are wrapped into[PSObject]insideForEach-Objectcmdlet. Likely becauseInputObjectparameter ofForEach-Objecttyped as[PSObject]andForEach-Objectdoes not do unwrapping.
– PetSerAl
Nov 12 '18 at 19:43
1
1
[PSCustomObject] is an alias for [System.Management.Automation.PSObject], but not to [System.Management.Automation.PSCustomObject]. So, that means that all four are wrapped into [PSObject] inside ForEach-Object cmdlet. Likely because InputObject parameter of ForEach-Object typed as [PSObject] and ForEach-Object does not do unwrapping.– PetSerAl
Nov 12 '18 at 19:43
[PSCustomObject] is an alias for [System.Management.Automation.PSObject], but not to [System.Management.Automation.PSCustomObject]. So, that means that all four are wrapped into [PSObject] inside ForEach-Object cmdlet. Likely because InputObject parameter of ForEach-Object typed as [PSObject] and ForEach-Object does not do unwrapping.– PetSerAl
Nov 12 '18 at 19:43
add a comment |
1 Answer
1
active
oldest
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PetSerAl, as he frequently does, has provided the crucial pointer in a comment:
Piping objects to ForEach-Object wraps them in a [psobject] instance, which causes -is [pscustomobject] / -is [psobject] to return $True for any input object, because - confusingly - [pscustomobject] is the same as [psobject]: they're both type accelerators for [System.Management.Automation.PSObject] - against what one would expect,[pscustomobject] is not short for [System.Management.Automation.PSCustomObject].
Therefore, test the input objects for being instances of [System.Management.Automation.PSCustomObject] rather than [pscustomobject]:
$a | ForEach-Object {
$_ -is [System.Management.Automation.PSCustomObject]
}
Note that if you use a foreach loop, even -is [pscustomobject] would work, because the objects being enumerated are then not wrapped in an extra [psobject] instance:
foreach ($element in $a) {
$element -is [pscustomobject]
}
This works, because even a bona fide [System.Management.Automation.PSCustomObject] is technically also a [System.Management.Automation.PSObject] behind the scenes.
answered Nov 13 '18 at 4:45
mklement0mklement0
128k20241270
add a comment |
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PetSerAl, as he frequently does, has provided the crucial pointer in a comment:
Piping objects to ForEach-Object wraps them in a [psobject] instance, which causes -is [pscustomobject] / -is [psobject] to return $True for any input object, because - confusingly - [pscustomobject] is the same as [psobject]: they're both type accelerators for [System.Management.Automation.PSObject] - against what one would expect,[pscustomobject] is not short for [System.Management.Automation.PSCustomObject].
Therefore, test the input objects for being instances of [System.Management.Automation.PSCustomObject] rather than [pscustomobject]:
$a | ForEach-Object {
$_ -is [System.Management.Automation.PSCustomObject]
}
Note that if you use a foreach loop, even -is [pscustomobject] would work, because the objects being enumerated are then not wrapped in an extra [psobject] instance:
foreach ($element in $a) {
$element -is [pscustomobject]
}
This works, because even a bona fide [System.Management.Automation.PSCustomObject] is technically also a [System.Management.Automation.PSObject] behind the scenes.
answered Nov 13 '18 at 4:45
mklement0mklement0
128k20241270
add a comment |
PetSerAl, as he frequently does, has provided the crucial pointer in a comment:
Piping objects to ForEach-Object wraps them in a [psobject] instance, which causes -is [pscustomobject] / -is [psobject] to return $True for any input object, because - confusingly - [pscustomobject] is the same as [psobject]: they're both type accelerators for [System.Management.Automation.PSObject] - against what one would expect,[pscustomobject] is not short for [System.Management.Automation.PSCustomObject].
Therefore, test the input objects for being instances of [System.Management.Automation.PSCustomObject] rather than [pscustomobject]:
$a | ForEach-Object {
$_ -is [System.Management.Automation.PSCustomObject]
}
Note that if you use a foreach loop, even -is [pscustomobject] would work, because the objects being enumerated are then not wrapped in an extra [psobject] instance:
foreach ($element in $a) {
$element -is [pscustomobject]
}
This works, because even a bona fide [System.Management.Automation.PSCustomObject] is technically also a [System.Management.Automation.PSObject] behind the scenes.
answered Nov 13 '18 at 4:45
mklement0mklement0
128k20241270
add a comment |
PetSerAl, as he frequently does, has provided the crucial pointer in a comment:
Piping objects to ForEach-Object wraps them in a [psobject] instance, which causes -is [pscustomobject] / -is [psobject] to return $True for any input object, because - confusingly - [pscustomobject] is the same as [psobject]: they're both type accelerators for [System.Management.Automation.PSObject] - against what one would expect,[pscustomobject] is not short for [System.Management.Automation.PSCustomObject].
Therefore, test the input objects for being instances of [System.Management.Automation.PSCustomObject] rather than [pscustomobject]:
$a | ForEach-Object {
$_ -is [System.Management.Automation.PSCustomObject]
}
Note that if you use a foreach loop, even -is [pscustomobject] would work, because the objects being enumerated are then not wrapped in an extra [psobject] instance:
foreach ($element in $a) {
$element -is [pscustomobject]
}
This works, because even a bona fide [System.Management.Automation.PSCustomObject] is technically also a [System.Management.Automation.PSObject] behind the scenes.
answered Nov 13 '18 at 4:45
mklement0mklement0
128k20241270
PetSerAl, as he frequently does, has provided the crucial pointer in a comment:
Piping objects to ForEach-Object wraps them in a [psobject] instance, which causes -is [pscustomobject] / -is [psobject] to return $True for any input object, because - confusingly - [pscustomobject] is the same as [psobject]: they're both type accelerators for [System.Management.Automation.PSObject] - against what one would expect,[pscustomobject] is not short for [System.Management.Automation.PSCustomObject].
Therefore, test the input objects for being instances of [System.Management.Automation.PSCustomObject] rather than [pscustomobject]:
$a | ForEach-Object {
$_ -is [System.Management.Automation.PSCustomObject]
}
Note that if you use a foreach loop, even -is [pscustomobject] would work, because the objects being enumerated are then not wrapped in an extra [psobject] instance:
foreach ($element in $a) {
$element -is [pscustomobject]
}
This works, because even a bona fide [System.Management.Automation.PSCustomObject] is technically also a [System.Management.Automation.PSObject] behind the scenes.
answered Nov 13 '18 at 4:45
mklement0mklement0
128k20241270
edited Nov 13 '18 at 4:54
answered Nov 13 '18 at 4:45
mklement0mklement0
128k20241270
answered Nov 13 '18 at 4:45
mklement0mklement0
128k20241270
answered Nov 13 '18 at 4:45
mklement0mklement0
128k20241270
128k20241270
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[PSCustomObject]is an alias for[System.Management.Automation.PSObject], but not to[System.Management.Automation.PSCustomObject]. So, that means that all four are wrapped into[PSObject]insideForEach-Objectcmdlet. Likely becauseInputObjectparameter ofForEach-Objecttyped as[PSObject]andForEach-Objectdoes not do unwrapping.– PetSerAl
Nov 12 '18 at 19:43