How to: cross-platform compatible syntax:
sed -e ':a' -e 'N' -e '$!ba' -e 's/\n/ /g' /path/to/file
```

- `:a` create a label `a`
- `N` append the next line to the pattern space
- `$!` if not the last line, ba branch (go to) label `a`
- `s` substitute, `/\n/` regex for new line, `/ /` by a space, `/g` global match (as many times as it can)

Alternatives:

```bash