Unix newlines to Windows newlines (on Windows)

There is dos2unix and unix2dos in Cygwin.

Here is the pure PowerShell way if you are interested.

Finding files with at least one Unix line ending (PowerShell v1):

dir * -inc *.txt | %{ if (gc $_.FullName -delim "`0" | Select-String "[^`r]`n") {$_} }

Here is how you find and covert Unix line endings to Windows line endings. One important thing to note is that an extra line ending (\r\n) will be added to the end of the file if there isn't already a line ending at the end. If you really don't want that, I'll post an example of how you can avoid it (it is a bit more complex).

Get-ChildItem * -Include *.txt | ForEach-Object {
    ## If contains UNIX line endings, replace with Windows line endings
    if (Get-Content $_.FullName -Delimiter "`0" | Select-String "[^`r]`n")
    {
        $content = Get-Content $_.FullName
        $content | Set-Content $_.FullName
    }
}

The above works because PowerShell will automatically split the contents on \n (dropping \r if they exist) and then add \r\n when it writes each thing (in this case a line) to the file. That is why you always end up with a line ending at the end of the file.

Also, I wrote the above code so that it only modifies files that it needs to. If you don't care about that you can remove the if statement. Oh, make sure that only files get to the ForEach-Object. Other than that, you can do whatever filtering you want at the start of that pipeline.