Can't Activate Plugin

[jamiejackson]

I've never used a vim plugin. What am I doing wrong here?

[jamie.jackson@devstack bundle]$ curl -fLo ~/.vim/autoload/plug.vim --create-dirs \
>     https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 78763  100 78763    0     0   540k      0 --:--:-- --:--:-- --:--:--  541k
[jamie.jackson@devstack bundle]$ echo "Plug 'will133/vim-dirdiff'" >> ~/.vimrc
[jamie.jackson@devstack bundle]$ vim -c "DirDiff secrets/stacks/test2 secrets/stacks/test1"
Error detected while processing /home/jamie.jackson/.vimrc:
line    1:
E492: Not an editor command: Plug 'will133/vim-dirdiff'
Press ENTER or type command to continue
[jamie.jackson@devstack bundle]$ vim --version
VIM - Vi IMproved 7.4 (2013 Aug 10, compiled Aug  9 2019 03:17:15)

[jamiejackson]

[jamie.jackson@devstack bundle]$ mkdir -p ~/.vim/autoload ~/.vim/bundle && \
> curl -LSso ~/.vim/autoload/pathogen.vim https://tpo.pe/pathogen.vim
[jamie.jackson@devstack bundle]$ echo "execute pathogen#infect()
> syntax on
> filetype plugin indent on" >> ~/.vimrc
[jamie.jackson@devstack bundle]$ cd ~/.vim/bundle
[jamie.jackson@devstack bundle]$ git clone git://github.com/will133/vim-dirdiff
Cloning into 'vim-dirdiff'...
remote: Enumerating objects: 25, done.
remote: Counting objects: 100% (25/25), done.
remote: Compressing objects: 100% (13/13), done.
remote: Total 158 (delta 7), reused 21 (delta 7), pack-reused 133
Receiving objects: 100% (158/158), 111.76 KiB | 0 bytes/s, done.
Resolving deltas: 100% (50/50), done.
[jamie.jackson@devstack bundle]$ vim -c "DirDiff  /home/docker/secrets/stacks/test2 /home/docker/secrets/stacks/test1"

Once in, I get this at the bottom of the output:

line    4:
E117: Unknown function: bufwinid
E15: Invalid expression: bufwinid(a:fname)
line    5:
E121: Undefined variable: winid
E15: Invalid expression: winid > 0
Error detected while processing function <SNR>12_DirDiff..<SNR>12_DirDiffNext..<SNR>12_DirDiffOpen:
line   96:
E121: Undefined variable: b:currentDiff
E15: Invalid expression: (b:currentDiff)

Striking out here.

[will133]

Never mind what I said. I think it may be that your vim is somewhat old. Can you upgrade your vim?