Powershell Select-string text file

Try the following, which combines use of the common -PipelineVariable parameter with calculated properties:

Get-ChildItem -PipelineVariable file -File $directory -Recurse |
  Select-String -Pattern (Get-Content -Path 'C:\Patterns.txt') | 
    Select-Object Pattern,
                  @{ Name='Fullname';  Expression = { $file.FullName } },                  
                  @{ Name='Extension'; Expression = { $file.Extension } }

Pipe the above to Export-Csv as needed.

• -PipelineVariable file stores each file-info object emitted by Get-ChildItem in variable $file, allowing it to be referenced in a script block in a later pipeline segment.

• The expressions defining the values of the calculated properties in the Select-Object call reference the file-info object stored in pipeline variable $file in order to create output objects that combine the Pattern property from the Select-String output objects with property values from the input file at hand.

As for what you tried:

• Your primary problem was your attempt to pipe custom objects ([pscustomobject] instances) to Select-String, which causes the latter to search through the stringified representation of the custom objects (which yields a string like '@{Fullname = ...; extension = ...}', as shown in your question^[1]) - rather than treating them as representing files whose content you want to search.

  • To achieve that, you must use file-info objects ([System.IO.FileInfo] instances) as input, as directly emitted by Get-ChildItem.

  • For the sake of completeness:

    • If your non-file-info input objects have a property reflecting the file path of interest, such as in your case, you can make this work, namely via a delay-bind script block passed to Select-String's -LiteralPath parameter:
      $files | Select-String -LiteralPath { $_.Fullname } ...
    • Similarly, if your custom objects had a LiteralPath (or PSPath or, in PowerShell (Core) 7+, LP) property containing the file path of interest, piping it Select-String should work as-is, because that property's value should automatically bind to the -LiteralPath parameter (this mechanism, in fact, is how System.IO.FileInfo instances bind to -LiteralPath - see this answer for an explanation); however, as of PowerShell 7.2.2, this appears to be broken with Select-String, specifically: see GitHub issue #17188.

• The secondary problem is that your Select-Object call operates only on the output objects emitted by Select-String, which are [Microsoft.PowerShell.Commands.MatchInfo] instances, which do not have .Fullname and .Extension properties.

^{[1] Note that this string representation is the result of simple .ToString() stringification; it is not the rich representation you would see in the console, courtesy of PowerShell's for-display output formatting system. This surprising behavior is discussed in detail in this answer.}

This feels wrong somehow, but it works. I have a feeling there's a better way to convert the Line property to a hashtable object, but I tried both Invoke-Expression and ConvertFrom-StringData with no success.

$directory = 'c:\test', 'd:\test\test'   
$files = Get-ChildItem -File $directory | Select-Object FullName, Extension
$exportObj = $files | Select-String -Pattern $patterns | Select-Object Pattern, Line | %{
    $line = $_.Line -replace "[@,{,}]","" -split ";"
    [PSCustomObject]@{
            Pattern=$_.Pattern
            FullName=($line[0] -split "=")[1]
            Extension=($line[1] -split "=")[1]
        }
    }
$exportObj | Export-Csv -Path C:\temp\test.csv -NoTypeInformation