Compare two text files in Powershell and if a name is found in both files output content from file 2 to a 3rd text file

Question

Is it possible using PowerShell to compare the contents of two text files line by line and if a line is found output that line to a third text file?
Lets say hypothetically someone asks us to search a text file named names1.txt and when a name is found in names1.txt we then pair that with the same name in the second text file called names2.txt
lets say the names shown below are in names1.txt
Bob
Mike
George
Lets say the names and contents shown below are in names2.txt
Lisa
Jordan
Mike 1112222
Bob 8675309
Don
Joe
Lets say we want names3.txt to contain the data shown below
Mike 1112222
Bob 8675309
In vbscript I used search and replace commands to get part of the way there like this
Set objFSO = CreateObject("Scripting.FileSystemObject")
Set objFile = objFSO.OpenTextFile("testing.txt", ForReading)
strText = objFile.ReadAll
objFile.Close
strNewText = Replace(strText, "Mike ", "Mike 1112222")
Set objFile = objFSO.OpenTextFile("testing.txt", ForWriting)
objFile.WriteLine strNewText
objFile.Close
That script works great when you know the name you are looking for and the correct values. Lets say someone gives you a list of 1000 employees and says import these names into a list in the correct format and one sheet has the correct names only and
the other sheet has lots of extra names say 200000 and you only need the 1000 you are looking for in the format from names2.txt.

Answer 1

Sure,
Here's a simple one:
$names1 = "C:\names1.txt"
$names2 = "C:\names2.txt"
$names3 = "C:\names3.txt"
Get-Content $names1 | ForEach-Object {
$names1_Line = $_
Get-Content $names2 | Where-Object {$_.Contains($names1_Line)} | Out-File -FilePath $names3 -Append
This basically just reads $names1 file, line by line, and then read $names2 file line by line as well.
If the line being evaluated from $names2 file contains the line being evaluated from $names1 file, then the line from $names2 file gets output to $names3 file, appending to what's already there.
This might need a few more tinkering to get it to perform faster etc depending on your requirements. For example:
- If either $names1 or $names2 contain a lot of entries (in the region of hundreds) then it will be faster to load the whole content of $names2 into memory rather than opening the file, reading line by line, closing and then doing the same for every single
line in $names1 (which is how it is currently works)
- Make sure that your comparison is behaving as expected. The .Contains method always does a case sensitive comparison, this might not be what you are after.
- You might want to put a condition to ignore blank lines or lines with spaces, else they'll also be brought over to $names3
Hopefully this will get you started though and ask if you have further questions.
Fausto