Comment and uncomment lines

Source

https://stackoverflow.com/a/27355109/12780516

to comment a line (and preserve indentation)
```
sed -Ei '/<pattern>/s/^(\s*)/\1# /g'
```
to uncomment a line (and preserve indentation)
```
sed -Ei '/<pattern>/s/^(\s*)#\s?/\1/g'
```