I tried to look for this but couldn't find anything that would suit me. 
My problem is that i need to convert content of multiple files that have the extension `.txt` to one line, for example:

```
1
2
3
4

```

I would like to convert to `1234` or `1 2 3 4`.

I also have subfolders that I would like to be included. I tried multiple attempts with Linux, and even tried TextCrawler 3 for Windows, but nothing really helped me.