Format output display

Hi developer,

Here is my logic script:
$fileList = dir 'H:\aa.txt'

$regex = "(([-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?))|((?<=\"")((\w+(\s+\w+)?|\d+))(?<!\""))|[a-zA-Z]+|(?<=\"")(?=\"")"
foreach ($file in $fileList){
    $matchInfo = @((Get-Content $file) | ForEach-Object{ $_.Trim()}| Select-String -Pattern  $regex -AllMatches)
    $output = foreach($minfo in $matchInfo){
                foreach($match in @($minfo.Matches | Foreach {$_.Groups[0].value})){
                    $match 
                }
            }
    $output
}

where aa.txt:
aa aa aa
bb bb bb

I run it and display output like this:

aa aa aa bb bb bb

But i need to display output like this:

aa,aa,aa
bb,bb,bb

Any Idea?
Thanks