Compare Text Files. Record Line #s that Match - powershell

Question

I have two text files.
$File1 = "C:\Content1.txt"
$File2 = "C:\Content2.txt"
I'd like to compare these to see if they have the same number of lines and then I'd like to record the line number of each line that matches. I realize that sounds ridiculous but this is what I've been asked to do at my work.
I can compare them a lot of ways. I decided to do the following:
$File1Lines = Get-Content $File1 | Measure-Object -Line
$File2Lines = Get-Content $File2 | Measure-Object -Line
I'd like to test it with an if statement so that if they don't match, then I can start an earlier process over again.
if ($file1lines.lines -eq $file2lines.lines)
{ Get the Line #s that match and proceed to the next step}
else {Start Over}
I'm unsure how to record the line #s that match. Any thoughts on how to do this?

Answer 1

This is really pretty simple since Get-Content reads the file in as an array of strings, and you can index that array simply enough.
Do{
<stuff to generate files>
}While(($File1 = GC $PathToFile1).Count -ne ($File2 = GC $PathToFile2).count)
$MatchingLineNumbers = 0..($File1.count -1) | Where{$File1[$_] -eq $File2[$_]}
Since arrays in PowerShell use a 0 based index we want to start at 0 and go for however many lines the files have. Since .count starts at 1 not 0 we need to subtract 1 from the total count. So if your file has 27 lines $File1.count will equal 27. The index for those lines ranges from 0 (first line) to 26 (last line). The code ($File1.count - 1) would effectively come out to 26, so 0..26 starts at 0, and counts to 26.
Then each number goes to a Where statement that checks that specific line in each file to see if they are equal. If they are then it passes the number along, and that gets collected in $MatchingLineNumbers. If the lines don't match the number isn't passed along.

Answer 2

You'll need to get an intersection first, then find the index.
file1.txt
Line1
Line2
Line3
Line11
Line21
Line31
Line12
Line22
Line32
file2.txt
Line1
Line11
Line21
Line31
Line12
Line222
Line323
Line214
Line315
Line12
Line22
Line32
test.ps1
$file1 = Get-Content file1.txt
$file2 = Get-Content file2.txt
$matchingLines = $file1 | ? { $file2 -contains $_ }
$file1Lines = $matchingLines | % { Write-Host "$([array]::IndexOf($file1, $_))" }
$file2Lines = $matchingLines | % { Write-Host "$([array]::IndexOf($file2, $_))" }
Output
$file1Lines
0
3
4
5
6
7
8
$file2Lines
0
1
2
3
4
10
11