How to run a function without getting prompted to continue?

Question

In order to keep my tags file up to date I wrote this function which runs ctags -R . whenever I save a file.

function! UpdateCtags()
    " assume if a tags file exists - then current dir is ok
    if filereadable("tags")
        echo "updating tags file"
        call system('ctags -R .')
    else
        echo "unable to update tags file - probably wrong current dir"
    endif
endfunction

au BufWritePost * silent! call UpdateCtags()

The function seems to work ok, but it triggers a prompts

"somefile" 508L, 16090C written  
updating tags file  
Press ENTER or type command to continue

Its not a major problem, but considering I save a file probably every 15 seconds, I want a message confirming the function ran to be printed, but I don't want to be interupted by a prompt.
.
Is it possible to make this prompt go away?

Ive tried adding silent! to the autocmd

au BufWritePost * silent! call UpdateCtags()

But it seems to have no effect

Answer 1

After reading this vim.wikia.com article, I learnt that the cause of the prompt is content in the command line exceeding the available commandline height

so I added set cmdheight=2 to the function to this and it now seems to work

if filereadable("tags")
    set cmdheight=2
    "^^^^^^^^^^^^^^^^
    echo "updating tags file"
    call system('ctags -R .')
    set cmdheight=1
    "^^^^^^^^^^^^^^^
else