find all files and lines that contains a specific string

It's critical that if you are new, that you first spend the time to ramp up to prevent a lot of unnecessary frustration and confusion you are going to encounter.

Do a search on Microsoft Virtual Academy on PowerShell and YouTube for no cost video training.

Here are some other resources and advice:

• Free eBooks are available on this site
• Read the full help file on any cmdlet you are trying to use
• Practice with the examples
• Read the helpfile again
• Pick up a few good books, like, 'PowerShell in a Month of Lunches'.
• There are lots of free PowerShell eBooks on Microsoft's websites and others.

See also: The PowerShell Survival Guide

As for a specific example on your question. How about this approach?

$searchWords = @('Hello','Client')

Foreach ($sw in $searchWords)
{
    Get-Childitem -Path "d:\temp" -Recurse -include "*.txt","*.csv" | 
    Select-String -Pattern "$sw" | 
    Select Path,LineNumber,@{n='SearchWord';e={$sw}}
}


# Partial Results

Path                                            LineNumber SearchWord
----                                            ---------- ----------
D:\temp\Duplicates\BeforeRename1\PsGet.txt             157 Hello     
D:\temp\Duplicates\BeforeRename1\PsGet.txt             161 Hello     
D:\temp\Duplicates\BeforeRename1\StringText.txt          1 Hello     
D:\temp\Duplicates\PoSH\PsGet.txt                      157 Hello     
D:\temp\Duplicates\PoSH\PsGet.txt                      161 Hello     
D:\temp\Duplicates\PoSH\StringText.txt                   1 Hello     
...    
D:\temp\Duplicates\BeforeRename1\PoSH-Get-Mo...        108 Client    
D:\temp\Duplicates\BeforeRename1\Powershell ...         12 Client    
D:\temp\Duplicates\BeforeRename1\Powershell ...         15 Client    
... 
D:\temp\Duplicates\BeforeRename1\WindowsFeat...         92 Client    
D:\temp\Duplicates\BeforeRename1\WindowsFeat...         94 Client    
D:\temp\Duplicates\BeforeRename1\WindowsFeat...        149 Client    
D:\temp\Duplicates\BeforeRename1\WindowsFeat...        157 Client    
D:\temp\Duplicates\BeforeRename1\WindowsFeat...        191 Client    
D:\temp\Duplicates\BeforeRename1\WindowsFeat...        239 Client    
D:\temp\Duplicates\BeforeRename1\WindowsFeat...        241 Client