The Vim shfmt plugin runs shfmt to auto format the current buffer by a command :Shfmt. If instead you prefer to format a textobject, say a paragraph, by gq, then add to the file after/ftplugin/sh.vim in your Vim configuration folder the lines

if executable('shfmt')
  let &l:formatprg='shfmt -i ' . &l:shiftwidth . ' -ln posix -sr -ci -s'
endif

and press, say gqip. Customize the options -ln posix -sr -ci -s to your liking.

You just need the shfmt command

Obtain a copy of this plugin and place shfmt.vim in your Vim plugin directory or be sensible and use something like Plug:

Plug 'z0mbix/vim-shfmt', { 'for': 'sh' }

You can use the :Shfmt command to run shfmt and automatically format the current buffer

You can also use the :Shfmt command together with options. For example,

:Shfmt -p

:Shfmt -i 2

shfmt uses tabs by default for auto formatting, so if you prefer to use 2 spaces, you can set the following in your .vimrc file:

let g:shfmt_extra_args = '-i 2'

If you would like to auto format shell scripts on save, you can add the following to your vim config:

let g:shfmt_fmt_on_save = 1

The Vim shfmt plugin is open-sourced software licensed under the MIT license.