Related
I'm writing a function to Write-EventLog with the information changing depending on arguments. One of those arguments is the message, but it will not display in the actual event log. Only the string portion that's hard coded.
I've tried assigning it to a variable and outputting it to make sure it's there and it shows that even though the variable type is string it won't concatenate in the function.
$testmsg1 = "The script successfully completed an operation"
Function Log-This($level, $message){
If ($level -eq "Information"){
$testmsg1
$msg = "INFO: $message"
$msg
Write-EventLog -LogName Application `
-EventId 1099 `
-EntryType Information `
-Message $msg `
-Source "Windows Error Reporting"
}
...
}
$testmsg1.GetType()
Log-This "Information", $testmsg1
This produces:
IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True True String System.Object
The script successfully completed an operation
INFO:
What I'm going for is the string "INFO: The script successfully completed an operation". What am I doing wrong to not have the string concatenate?
When evoking the function you need to identify the parameters for it individually.
e.g.
Log-This -level "Information" -message $testmsg1
Thanks #js2010 for pointing that out.
Don't use a comma in the function call either.
I have a log file called log.json that's formatted like this:
{"msg": "Service starting up!"}
{"msg": "Running a job!"}
{"msg": "Error detected!"}
And another file called messages.json, which looks like this:
{"msg": "Service starting up!", "out": "The service has started"}
{"msg": "Error detected!", "out": "Uh oh, there was an error!"}
{"msg": "Service stopped", "out": "The service has stopped"}
I'm trying to write a function using jq that reads in both files, and whenever it finds a msg in log.json that matches a msg in messages.json, print the value of out in the corresponding line in messages.json. So, in this case, I'm hoping to get this as output:
"The service has started"
"Uh oh, there was an error!"
The closest that I've been able to get so far is the following:
jq --argfile a log.json --argfile b messages.json -n 'if ($a[].msg == $b[].msg) then $b[].out else empty end'
This successfully performs all of the comparisons that I'm hoping to make. However, rather than printing the specific out that I'm looking for, it instead prints every out whenever the if statement returns true (which makes sense. $b[].out was never redefined, and asks for each of them). So, this statement outputs:
"The service has started"
"Uh oh, there was an error!"
"The service has stopped"
"The service has started"
"Uh oh, there was an error!"
"The service has stopped"
So at this point, I need some way to ask for $b[current_index].out, and just print that. Is there a way for me to do this (or an entirely seperate approach that I can use)?
messages.json effectively defines a dictionary, so let's begin by creating a JSON dictionary which we can lookup easily. This can be done conveniently using INDEX/2 which (in case your jq does not have it) is defined as follows:
def INDEX(stream; idx_expr):
reduce stream as $row ({};
.[$row|idx_expr|
if type != "string" then tojson
else .
end] |= $row);
A first-cut solution is now straightforward:
INDEX($messages[]; .msg) as $dict
| inputs
| $dict[.msg]
| .out
Assuming this is in program.jq, an appropriate invocation would be as follows (note especially the -n option):
jq -n --slurpfile messages messages.json -f program.jq log.json
The above will print null if the .msg in the log file is not in the dictionary. To filter out these nulls, you could (for example) add select(.) to the pipeline.
Another possibility would be to use the original .msg, as in this variation:
INDEX($messages[]; .msg) as $dict
| inputs
| . as $in
| $dict[.msg]
| .out // $in.msg
I'm trying to dynamically parse & build-up a data structure of some incoming JSON files I'm to be supplied with (that'll be in non-standard structure) via Powershell to then process the data in those files & hand them over to the next step.
As part of that, I'm trying to build up the data structure of the JSON file into essentially a list of of data-paths for me to parse through & grab the data out of, so that I can cope with arrays, nested JSON objects and so on. So far so good.
Where I fall into some sort of Powershell peculiarity is in handling 2+ levels of depth via a variable. Let me give you a nice code-block to demonstrate the problem...
# Generate a Quick JSON file with different data types & levels
[object]$QuickJson = #'
{
"Name" : "I am a JSON",
"Version" : "1.2.3.4",
"SomeBool" : true,
"NULLValue" : null,
"ArrayOfVersions" : [1.0,2.0,3.0],
"MyInteger" : 69,
"NestedJSON" : {
"Version" : 5.0,
"IsReady" : false
},
"DoubleNestedJSON" : {
"FirstLevel" : 1,
"DataValue" : "I am at first nested JSON level!",
"Second_JSON_Level" : {
"SecondLevel" : 2,
"SecondDataValue" : "I am on the 2nd nested level"
}
}
}
'#
# Import our JSON file into Powershell
[object]$MyPSJson = ConvertFrom-Json -InputObject $QuickJson
# Two quick string variables to access our JSON data paths
[string]$ShortJsonPath = "Name"
[string]$NestedJsonPath = "NestedJson.Version"
# Long string to access a double-nested JSON object
[string]$LongNestedJsonPath = "DoubleNestedJSON.Second_JSON_Level.SecondDataValue"
# Both of these work fine
Write-Host ("JSON Name (Direct) ==> " + $MyPSJson.Name)
Write-Host ("JSON Name (via Variable) ==> " + $MyPSJson.$ShortJsonPath)
# The following way to access a single nested Json Path works fine
Write-Host ("Nested JSON Version (via direct path) ==> " + $MyPSJson.NestedJson.Version)
# And THIS returns an empty line / is where I fall afoul of something in Powershell
Write-Host ("Nested JSON Version (via variable) ==> " + $MyPSJson.$NestedJsonPath)
# Other things I tried -- all returning an empty line / failing in effect
Write-Host ("Alternate Nested JSON Version ==> " + $($MyPSJson.$NestedJsonPath))
Write-Host ("Alternate Nested JSON Version ==> " + $MyPSJson.$($NestedJsonPath))
Write-Host ("Alternate Nested JSON Version ==> " + $($MyPSJson).$($NestedJsonPath))
# Similarly, while THIS works...
$MyPSJson | select-object -Property NestedJSON
# This will fail / return me nothing
$MyPSJson | select-object -Property NestedJSON.Version
... in doing a bunch of research around this, I came across a suggestion to transform this into a Hashtable -- but that has the same problem, sadly. So with the above code-snippet, the following will transform the JSON object into a hashtable.
# Same problem with a hash-table if constructed from the JSON file...
[hashtable]$MyHash = #{}
# Populate $MyHash with the data from our quickie JSON file...
$QuickJson | get-member -MemberType NoteProperty | Where-Object{ -not [string]::IsNullOrEmpty($QuickJson."$($_.name)")} | ForEach-Object {$MyHash.add($_.name, $QuickJson."$($_.name)")}
# ... and even then -- $MyHash."$($NestedJsonPath)" -- fails, while a single level deep string works fine in the variable! :(
So it's pretty clear that I'm running into "something" of a Powershell internal logic problem, but I can't get Powershell to be overly helpful in WHY that is. Adding a '-debug' or similar in an attempt to increase verbosity hasn't helped shed light on this.
I suspect it's something akin to the items raised in this article here ( https://blogs.technet.microsoft.com/heyscriptingguy/2011/10/16/dealing-with-powershell-hash-table-quirks/ ) but just specific with variables.
I've not had any luck in finding anything obvious in the Powershell language specification (3.0 still being the latest from here as far as I can tell -- https://www.microsoft.com/en-usdownload/details.aspx?id=36389 ) either. It may be in there, I may just miss it.
Any advice in how to get Powershell to play nice with this would be greatly appreciated. I'm not sure how / why Powershell is fine with a simple string but seems to have issues with a 'something.somethingelse' type string here.
Thank you.
Further notes & addenda to the original:
It seems there are several issues to attack. One is "dealing with a single nested level". The "quick fix" for that seems to be using "Invoke-Expression" to resolve the statement, so for instance (IMPORTANT - take note of the back-tick with the first variable!):
iex "`$MyPSJson.$NestedJsonPath"
That use of Invoke-Expression also works with multi-nested situations:
iex "`$MyPSJson.$LongNestedJsonPath"
An alternative approach that was mentioned is the use of multiple select statements ... but I've not been able to get that to work with multi-nested objects (Powershell seems to not resolve those properly for some reason).
So for instance in this scenario:
($MyComp | select $_.DoubleNestedJSON | select FirstLevel)
Powershell returns
FirstLevel
----------
... instead of the actual data value. So - for now, it seems that selects won't work with multi-level nested objects due to Powershell apparently not resolving them?
When you write something like
$MyPSJson.Name
this will attempt to retrieve the member named Name from the object $MyPSJson. If there is no such member, you'll get $null.
Now, when you do that with variables for the member name:
$MyPSJson.$ShortJsonPath
this works pretty much identical in that the member with the name stored in $ShortJsonPath is looked up and its value retrieved. No surprises here.
When you try that with a member that doesn't exist on the object, such as
$MyPSJson.$NestedJsonPath
# equivalent to
# $MyPSJson.'NestedJSON.Version'
you'll get $null, as detailed before. The . operator will only ever access a member of the exact object that is the result of its left-hand-side expression. It will never go through a member hierarchy in the way you seem to expect it to do. To be frank, I'm not aware of a language that works that way.
The reason it works with Invoke-Expression is, that you effectively converting the $NestedJsonPath string into part of an expression resulting in:
$MyPSJson.NestedJSON.Version
which Invoke-Expression then evaluates.
You can, of course, define your own function that works that way (and I'd much prefer that instead of using Invoke-Expression, a cmdlet that should rarely, if ever, used (heck, it's eval for PowerShell – few languages with eval advocate its use)):
function Get-DeepProperty([object] $InputObject, [string] $Property) {
$path = $Property -split '\.'
$obj = $InputObject
$path | %{ $obj = $obj.$_ }
$obj
}
PS> Get-DeepProperty $MyPSJson NestedJson.Version
5,0
You could even make it a filter, so you can use it more naturally on the pipeline:
filter Get-DeepProperty([string] $Property) {
$path = $Property -split '\.'
$obj = $_
$path | %{ $obj = $obj.$_ }
$obj
}
PS> $MyPSJson | Get-DeepProperty nestedjson.version
5,0
Why this doesn't work
When you provide the properties that you'd like within a string, like this
[string]$NestedJsonPath = "NestedJson.Version"
Powershell looks for a property called NestedJSon.Version. It's not actually traversing the properties, but looking for a string literal which contains a period. In fact, if I add a property like that to your JSON like so.
[object]$QuickJson = #'
{
"Name" : "I am a JSON",
"Version" : "1.2.3.4",
"SomeBool" : true,
"NULLValue" : null,
"ArrayOfVersions" : [1.0,2.0,3.0],
"MyInteger" : 69,
"NestedJSON.Version" : 69,
"NestedJSON" : {
"Version" : 5.0,
"IsReady" : false
}
}
I now get a value back, like so:
>$MyPSJson.$NestedJsonPath
69
The best way to get your values back is to use two separate variables, like this.
$NestedJson = "NestedJson"
$property = "Version"
>$MyPSJson.$NestedJson.$property
5.0
Or, alternatively, you could use select statements, as seen in the original answer below.
$MyPSJson | select $_.NestedJSON | select Version
Version
-------
1.2.3.4
If you use multiple Select-Object statements, they'll discard the other properties and allow you to more easily drill down to the value you'd like.
I followed Joey's filter example. However, I found it did not support accessing arrays.
Sharing the code that I got to work for this. Hopefully it will help others as well. Awesome thread!
filter Get-DeepProperty([string] $Property) {
$path = $Property -split '\.'
$obj = $_
foreach($node in $path){
if($node -match '.*\[\d*\]'){
$keyPieces = $node -split ('\[')
$arrayKey = $keyPieces[0]
$arrayIndex = $keyPieces[1] -replace ('\]','')
$obj = $obj.$arrayKey[$arrayIndex]
} else {
$obj = $obj.$node
}
}
$obj
}
Example usage:
$path = "nested.nestedtwo.steps[2]"
$payload | Get-DeepProperty $path
I had the same problem, so I wrote a function that does the trick.
It enables accessing any level of the json by variable path (string):
function getNestedJsonValue() {
param(
[Parameter(Mandatory = $true, ValueFromPipeline)] [PSCustomObject] $inputObj,
[Parameter(Mandatory = $true)] [string] $valuePath
)
if (($valuePath -eq $null) -or ($valuePath.length -eq 0) -or ($inputObj -eq $null)) {
return $inputObj
}
[System.Array] $nodes = "$valuePath" -split '\.'
foreach ($node in $nodes) {
if (($node -ne $null) -and ($node.length -gt 0) -and ($inputObj -ne $null)) {
$inputObj = $inputObj.$node
} else {
return $inputObj
}
}
return $inputObj
}
Usage: getNestedJsonValue -valuePath $nestedValuePath -inputObj $someJson
Pipe usage: $someJson | getNestedJsonValue -valuePath $nestedValuePath
An example nestedValuePath would be $nestedValuePath="some.nested.path"
Credit to wOxxOm for getting things on the right track.
Invoke-Expression does seem to work perfectly for this situation (if somewhat expensive, but that's fine in my personal example & situation), and it can cope with multiple levels of nesting.
So as examples for the above code snippet, the following will resolve just fine (Key point - pay attention to the initial back-tick. That caught me off guard):
Write-Host ("Single level JSON test ==> " + (iex "`$MyPSJson.$NestedJsonPath"))
Write-Host ("Double level JSON test ==> " + (iex "`$MyPSJson.$LongNestedJsonPath"))
That'll return our desired results:
Single level JSON test ==> 5.0
Double level JSON test ==> I am on the 2nd nested level
FoxDeploy's answer of using multi-level selects doesn't seem to work with 2+ levels of nesting, unfortunately for some bizarre reason.
Using:
($MyPSJson | select $_.DoubleNestedJSON | select FirstLevel)
We get the following back from Powershell:
FirstLevel
----------
... it seems that Powershell doesn't resolve nested objects in its entirety? We get a similar results if we intentionally use something that doesn't exist:
($MyPSJson | select $_.DoubleNestedJSON | select Doesnotexist)
... also simply returns:
Doesnotexist
------------
So - for now - it seems as if "Invoke-Expression" works most reliably (and most easily, as it's just a case of handing it a variable with the path'ed string).
I still can't explain the WHY of any of this so far (since I've used 'dotwalk'-ing with multiple variables through arrays quite happily), but at least there's a solution for now ... and that is Invoke-Expression !
The best (/least bad?) explanations for Invoke-Expression I've found so far are here (Microsoft's own description of the cmdlet doesn't really make a great job of hinting that it'd help in situations such as this):
http://ss64.com/ps/invoke-expression.html
https://www.adminarsenal.com/powershell/invoke-expression/
I'm trying to dynamically parse & build-up a data structure of some incoming JSON files I'm to be supplied with (that'll be in non-standard structure) via Powershell to then process the data in those files & hand them over to the next step.
As part of that, I'm trying to build up the data structure of the JSON file into essentially a list of of data-paths for me to parse through & grab the data out of, so that I can cope with arrays, nested JSON objects and so on. So far so good.
Where I fall into some sort of Powershell peculiarity is in handling 2+ levels of depth via a variable. Let me give you a nice code-block to demonstrate the problem...
# Generate a Quick JSON file with different data types & levels
[object]$QuickJson = #'
{
"Name" : "I am a JSON",
"Version" : "1.2.3.4",
"SomeBool" : true,
"NULLValue" : null,
"ArrayOfVersions" : [1.0,2.0,3.0],
"MyInteger" : 69,
"NestedJSON" : {
"Version" : 5.0,
"IsReady" : false
},
"DoubleNestedJSON" : {
"FirstLevel" : 1,
"DataValue" : "I am at first nested JSON level!",
"Second_JSON_Level" : {
"SecondLevel" : 2,
"SecondDataValue" : "I am on the 2nd nested level"
}
}
}
'#
# Import our JSON file into Powershell
[object]$MyPSJson = ConvertFrom-Json -InputObject $QuickJson
# Two quick string variables to access our JSON data paths
[string]$ShortJsonPath = "Name"
[string]$NestedJsonPath = "NestedJson.Version"
# Long string to access a double-nested JSON object
[string]$LongNestedJsonPath = "DoubleNestedJSON.Second_JSON_Level.SecondDataValue"
# Both of these work fine
Write-Host ("JSON Name (Direct) ==> " + $MyPSJson.Name)
Write-Host ("JSON Name (via Variable) ==> " + $MyPSJson.$ShortJsonPath)
# The following way to access a single nested Json Path works fine
Write-Host ("Nested JSON Version (via direct path) ==> " + $MyPSJson.NestedJson.Version)
# And THIS returns an empty line / is where I fall afoul of something in Powershell
Write-Host ("Nested JSON Version (via variable) ==> " + $MyPSJson.$NestedJsonPath)
# Other things I tried -- all returning an empty line / failing in effect
Write-Host ("Alternate Nested JSON Version ==> " + $($MyPSJson.$NestedJsonPath))
Write-Host ("Alternate Nested JSON Version ==> " + $MyPSJson.$($NestedJsonPath))
Write-Host ("Alternate Nested JSON Version ==> " + $($MyPSJson).$($NestedJsonPath))
# Similarly, while THIS works...
$MyPSJson | select-object -Property NestedJSON
# This will fail / return me nothing
$MyPSJson | select-object -Property NestedJSON.Version
... in doing a bunch of research around this, I came across a suggestion to transform this into a Hashtable -- but that has the same problem, sadly. So with the above code-snippet, the following will transform the JSON object into a hashtable.
# Same problem with a hash-table if constructed from the JSON file...
[hashtable]$MyHash = #{}
# Populate $MyHash with the data from our quickie JSON file...
$QuickJson | get-member -MemberType NoteProperty | Where-Object{ -not [string]::IsNullOrEmpty($QuickJson."$($_.name)")} | ForEach-Object {$MyHash.add($_.name, $QuickJson."$($_.name)")}
# ... and even then -- $MyHash."$($NestedJsonPath)" -- fails, while a single level deep string works fine in the variable! :(
So it's pretty clear that I'm running into "something" of a Powershell internal logic problem, but I can't get Powershell to be overly helpful in WHY that is. Adding a '-debug' or similar in an attempt to increase verbosity hasn't helped shed light on this.
I suspect it's something akin to the items raised in this article here ( https://blogs.technet.microsoft.com/heyscriptingguy/2011/10/16/dealing-with-powershell-hash-table-quirks/ ) but just specific with variables.
I've not had any luck in finding anything obvious in the Powershell language specification (3.0 still being the latest from here as far as I can tell -- https://www.microsoft.com/en-usdownload/details.aspx?id=36389 ) either. It may be in there, I may just miss it.
Any advice in how to get Powershell to play nice with this would be greatly appreciated. I'm not sure how / why Powershell is fine with a simple string but seems to have issues with a 'something.somethingelse' type string here.
Thank you.
Further notes & addenda to the original:
It seems there are several issues to attack. One is "dealing with a single nested level". The "quick fix" for that seems to be using "Invoke-Expression" to resolve the statement, so for instance (IMPORTANT - take note of the back-tick with the first variable!):
iex "`$MyPSJson.$NestedJsonPath"
That use of Invoke-Expression also works with multi-nested situations:
iex "`$MyPSJson.$LongNestedJsonPath"
An alternative approach that was mentioned is the use of multiple select statements ... but I've not been able to get that to work with multi-nested objects (Powershell seems to not resolve those properly for some reason).
So for instance in this scenario:
($MyComp | select $_.DoubleNestedJSON | select FirstLevel)
Powershell returns
FirstLevel
----------
... instead of the actual data value. So - for now, it seems that selects won't work with multi-level nested objects due to Powershell apparently not resolving them?
When you write something like
$MyPSJson.Name
this will attempt to retrieve the member named Name from the object $MyPSJson. If there is no such member, you'll get $null.
Now, when you do that with variables for the member name:
$MyPSJson.$ShortJsonPath
this works pretty much identical in that the member with the name stored in $ShortJsonPath is looked up and its value retrieved. No surprises here.
When you try that with a member that doesn't exist on the object, such as
$MyPSJson.$NestedJsonPath
# equivalent to
# $MyPSJson.'NestedJSON.Version'
you'll get $null, as detailed before. The . operator will only ever access a member of the exact object that is the result of its left-hand-side expression. It will never go through a member hierarchy in the way you seem to expect it to do. To be frank, I'm not aware of a language that works that way.
The reason it works with Invoke-Expression is, that you effectively converting the $NestedJsonPath string into part of an expression resulting in:
$MyPSJson.NestedJSON.Version
which Invoke-Expression then evaluates.
You can, of course, define your own function that works that way (and I'd much prefer that instead of using Invoke-Expression, a cmdlet that should rarely, if ever, used (heck, it's eval for PowerShell – few languages with eval advocate its use)):
function Get-DeepProperty([object] $InputObject, [string] $Property) {
$path = $Property -split '\.'
$obj = $InputObject
$path | %{ $obj = $obj.$_ }
$obj
}
PS> Get-DeepProperty $MyPSJson NestedJson.Version
5,0
You could even make it a filter, so you can use it more naturally on the pipeline:
filter Get-DeepProperty([string] $Property) {
$path = $Property -split '\.'
$obj = $_
$path | %{ $obj = $obj.$_ }
$obj
}
PS> $MyPSJson | Get-DeepProperty nestedjson.version
5,0
Why this doesn't work
When you provide the properties that you'd like within a string, like this
[string]$NestedJsonPath = "NestedJson.Version"
Powershell looks for a property called NestedJSon.Version. It's not actually traversing the properties, but looking for a string literal which contains a period. In fact, if I add a property like that to your JSON like so.
[object]$QuickJson = #'
{
"Name" : "I am a JSON",
"Version" : "1.2.3.4",
"SomeBool" : true,
"NULLValue" : null,
"ArrayOfVersions" : [1.0,2.0,3.0],
"MyInteger" : 69,
"NestedJSON.Version" : 69,
"NestedJSON" : {
"Version" : 5.0,
"IsReady" : false
}
}
I now get a value back, like so:
>$MyPSJson.$NestedJsonPath
69
The best way to get your values back is to use two separate variables, like this.
$NestedJson = "NestedJson"
$property = "Version"
>$MyPSJson.$NestedJson.$property
5.0
Or, alternatively, you could use select statements, as seen in the original answer below.
$MyPSJson | select $_.NestedJSON | select Version
Version
-------
1.2.3.4
If you use multiple Select-Object statements, they'll discard the other properties and allow you to more easily drill down to the value you'd like.
I followed Joey's filter example. However, I found it did not support accessing arrays.
Sharing the code that I got to work for this. Hopefully it will help others as well. Awesome thread!
filter Get-DeepProperty([string] $Property) {
$path = $Property -split '\.'
$obj = $_
foreach($node in $path){
if($node -match '.*\[\d*\]'){
$keyPieces = $node -split ('\[')
$arrayKey = $keyPieces[0]
$arrayIndex = $keyPieces[1] -replace ('\]','')
$obj = $obj.$arrayKey[$arrayIndex]
} else {
$obj = $obj.$node
}
}
$obj
}
Example usage:
$path = "nested.nestedtwo.steps[2]"
$payload | Get-DeepProperty $path
I had the same problem, so I wrote a function that does the trick.
It enables accessing any level of the json by variable path (string):
function getNestedJsonValue() {
param(
[Parameter(Mandatory = $true, ValueFromPipeline)] [PSCustomObject] $inputObj,
[Parameter(Mandatory = $true)] [string] $valuePath
)
if (($valuePath -eq $null) -or ($valuePath.length -eq 0) -or ($inputObj -eq $null)) {
return $inputObj
}
[System.Array] $nodes = "$valuePath" -split '\.'
foreach ($node in $nodes) {
if (($node -ne $null) -and ($node.length -gt 0) -and ($inputObj -ne $null)) {
$inputObj = $inputObj.$node
} else {
return $inputObj
}
}
return $inputObj
}
Usage: getNestedJsonValue -valuePath $nestedValuePath -inputObj $someJson
Pipe usage: $someJson | getNestedJsonValue -valuePath $nestedValuePath
An example nestedValuePath would be $nestedValuePath="some.nested.path"
Credit to wOxxOm for getting things on the right track.
Invoke-Expression does seem to work perfectly for this situation (if somewhat expensive, but that's fine in my personal example & situation), and it can cope with multiple levels of nesting.
So as examples for the above code snippet, the following will resolve just fine (Key point - pay attention to the initial back-tick. That caught me off guard):
Write-Host ("Single level JSON test ==> " + (iex "`$MyPSJson.$NestedJsonPath"))
Write-Host ("Double level JSON test ==> " + (iex "`$MyPSJson.$LongNestedJsonPath"))
That'll return our desired results:
Single level JSON test ==> 5.0
Double level JSON test ==> I am on the 2nd nested level
FoxDeploy's answer of using multi-level selects doesn't seem to work with 2+ levels of nesting, unfortunately for some bizarre reason.
Using:
($MyPSJson | select $_.DoubleNestedJSON | select FirstLevel)
We get the following back from Powershell:
FirstLevel
----------
... it seems that Powershell doesn't resolve nested objects in its entirety? We get a similar results if we intentionally use something that doesn't exist:
($MyPSJson | select $_.DoubleNestedJSON | select Doesnotexist)
... also simply returns:
Doesnotexist
------------
So - for now - it seems as if "Invoke-Expression" works most reliably (and most easily, as it's just a case of handing it a variable with the path'ed string).
I still can't explain the WHY of any of this so far (since I've used 'dotwalk'-ing with multiple variables through arrays quite happily), but at least there's a solution for now ... and that is Invoke-Expression !
The best (/least bad?) explanations for Invoke-Expression I've found so far are here (Microsoft's own description of the cmdlet doesn't really make a great job of hinting that it'd help in situations such as this):
http://ss64.com/ps/invoke-expression.html
https://www.adminarsenal.com/powershell/invoke-expression/
I am pretty new with PowerShell. I was recently tasked with making a error message popup that would help a local user determine whether or not a MS SQL on-demand DB merge worked or not. I wrote a script that woudld do the following:
Run the batch file that conducted the merge
Read the results of a text log file into a variable
Check the variable for any instances of the word "ERROR" and pop a success or fail dialog box depending on whether or not it found the word error in the log file.
Quick and simple I thought but I appear to be struggling with the conditional statement. Here is the script:
cmd /c c:\users\PERSON\desktop\merge.bat
$c = get-content c:\replmerg.log
if ($c -contains ("ERROR"))
{
$a = new-object -comobject wscript.shell
$b = $a.popup(“ERROR - Database Merge“,0,”Please Contact Support”,1)
}
else
{
$a = new-object -comobject wscript.shell
$b = $a.popup(“SUCCESS - Database Merge“,0,”Good Job!”,1)
}
Right now what happens is that the script runs and just skips to the Success message. I can confirm that simply running the 'get-content' command in powershell will on its own produce a variable that I can then call and show the content of the log file. My script however does not appear as though it is actually checking the $c variable for the word and then popping the error message as intended. What am I missing here?
Christian's answer is correct. You could also use the -match operator. For example:
if ((Get-Content c:\replmerg.log) -match "ERROR")
{
'do error stuff'
}
else
{
'do success stuff'
}
You can use -cmatch if you want a case sensitive comparison.
You actually don't need to use Get-Content at all. Select-String can take a -path parameter. I created two very simple text files, one which has the word ERROR and one which does not
PS C:\> cat .\noerror.txt
not in here
PS C:\> cat .\haserror.txt
ERROR in here
this has ERROR in here
PS C:\> if ( Select-String -Path .\noerror.txt -Pattern ERROR) {"Has Error"}
PS C:\> if ( Select-String -Path .\haserror.txt -Pattern ERROR) {"Has Error"}
Has Error
PS C:\>
The one thing that might trip you up is that the -pattern actually takes a regular expression, so be careful of what you use for your pattern. THis will find ERROR anywhere in the log file, even if there are multiple instances, like in my "haserror.txt" file.
The -contains operator is used for looking for an exact match in a list (or array). As the other answers indicate, you should use -match, -like, or -eq to compare strings.
You can use the -quiet switch of select-string if you just wnat to test for the presence of a string in a file.
select-string -path c:\replmerg.log -pattern "ERROR" -casesensetive -quiet
Will return $true if the string is found in the file, and $false if it is not.
contain operator test only an identical value (not part of a value).
You can try this
$c = get-content c:\replmerg.log | select-string "ERROR" -casesensitive
if ($c.length -gt 0)