I'm trying to create a mapping on Vim, that behaves like the following:

First of all I select a block of code or text using on Visual mode.
The I use this mapping to substitute the first column on each line for '#' effectively commenting each line.

Up until now I have the following:

```
vnoremap <Leader>c :normal! :s/^/#/<cr>

```

But for some reason it is not working. Nothing happens when I hit `<Leader>c` on a block of text. On the other hand, if I have:

```
vnoremap <Leader>c :normal! s/^/#/<cr>

```

it will for example subsitute:

```
The grey fox.

```

For

```
/^/#/he grey fox.

```

Any idea on how can I solve this issue?