Powershell - Strange output when using Get-ChildItem to search within files

Question

I have a problem I am hoping someone could help with....

I have a powershell script containing the lines shown below:

$output = Get-ChildItem -path $target -recurse | Select-String -pattern hello | group path | select name
Write-Output "Output from the string match is $output"

The error I am getting:

Output from the string match Microsoft.Powershell.Commands.GroupInfo Microsoft.Powershell.Commands.GroupInfo

When I run this command on it's own (ie not within a script) it works perfectly and returns the two files in that location that contains the word "hello".

It appears that it knows there are two things it has found because it prints the "Microsoft.Powershell.Commands.GroupInfo" text twice (as shown above in the error). But why is it printing this and not the path to the files as it should do?

There must be something obvious I am overlooking but I dont know what.

Your help is much appreciated, thanks

Answer 1

The reason you're seeing this is because $output is an array of Selected.Microsoft.PowerShell.Commands.GroupInfo objects -- the objects returned by Group-Object when passed to Select-Object (without Select-Object they would just be Microsoft.PowerShell.Commands.GroupInfo objects instead). You can confirm the type of objects in $ouput by running:

$output | Get-Member

Check the TypeName that is displayed at the top of the output.

When you run these commands interactively in the console, you are seeing the paths because PowerShell knows how to display GroupInfo objects in the console so that they are human-readable. Note that when you just call $output in the console, you see a "Name" header underlined with dash characters -- this is PowerShell interpreting the GroupInfo object you gave it and displaying the Name property for you in the console.

The problem occurs when you try to output the $output array inside a string. Then PowerShell is not able to use its more advanced formatting logic and instead merely tries to convert the object to a string to insert into your string. When it does that, it doesn't have enough logic to know that what you really want to appear in your string is the Name property of these GroupInfo objects, so instead if just prints out a string with the type name of each of the objects in the $output array. So that's why you see the type name twice.

The simple solution to this problem is the -ExpandProperty parameter for Select-Object. This does what it says -- it expands the property you asked for with Select-Object and returns just that property, not the parent object. So the Name property of a GroupInfo object is a string. If you call Select-Object Name, you get a GroupInfo object with the Name property. If you call Select-Object -ExpandProperty Name, you get just the Name property as a String object. Which is what I expect that you want in this case.

So try this instead:

$output = Get-ChildItem -path $target -recurse | Select-String -pattern hello | group path | select -ExpandProperty name

Answer 2

A foreach would be appropriate here I believe. Try this:

$output = Get-ChildItem -path $target -recurse | where {$_.name -like "*hello*"} | select name
foreach ($file in $output) {
   write-host $file.name
}

Or this:

$output = Get-ChildItem -path $target -recurse | select-string -pattern "hello" | select name
foreach ($file in $output) {
   write-output $file.name
}