Extract lines matching a pattern from all text files in a folder to a single output file

Question

I am trying to extract each line starting with "%%" in all files in a folder and then copy those lines to a separate text file. Currently using this code in PowerShell code, but I am not getting any results.

$files = Get-ChildItem "folder" -Filter *.txt
foreach ($file in $files)
{
if ($_ -like "*%%*")
{
Set-Content "Output.txt" 
}  
}

Answer 1

I think that mklement0's suggestion to use Select-String is the way to go. Adding to his answer, you can pipe the output of Get-ChildItem into the Select-String so that the entire process becomes a Powershell one liner.

Something like this:

Get-ChildItem "folder" -Filter *.txt | Select-String -Pattern '^%%' | Select -ExpandProperty line | Set-Content "Output.txt"