silent vs. silent! - What is the difference?

Question

This might be a silly question, or someone may say it lacks research, but I really cannot understand what does the exclamation mark after silent mean.

For example, in the following function that removes extra characters such as ^M:

function! RemoveExtraCharacters()
  let l:initialCol = getcurpos()[2]
  let l:line = getline('.')[0:initialCol-1]

  let l:numRemoved = len(l:line) - len(substitute(l:line, '[^[:print:]\t]', '', 'g'))

  let l:save = winsaveview()
  keeppatterns silent! %s/[^[:print:]\t]//g
  call winrestview(l:save)

  if l:numRemoved != 0
    call cursor(line('.'), (l:initialCol-l:numRemoved))
  endif
endfun
autocmd! BufWritePre * call RemoveExtraCharacters()

You can either use :silent or :silent! as a prefix to any command or you can add the e option to the substitute, which is often easier.

:%s/x/y/ge
:silent! %s/x/y/g
:silent %s/x/y/g

- https://stackoverflow.com/a/1043613

Answer 1

It's explained in :help :silent

                        *:sil* *:silent* *:silent!*
:sil[ent][!] {command}  Execute {command} silently.  Normal messages will not
            be given or added to the message history.
            When [!] is added, error messages will also be
            skipped, and commands and mappings will not be aborted
            when an error is detected.  |v:errmsg| is still set.
            When [!] is not used, an error message will cause
            further messages to be displayed normally.          

This is one of those examples where punctuation in the argument to :help makes a difference.

• :help silent takes you to the -silent help topic
• :help :silent takes you to the :silent command