My status line is getting erased, so I can't print function result

Question

I have a function that counts the number of matches in a file using the substitute Ex command with the /n flag and returns the value. However, I cannot echo the answer because the status line is getting overwritten by the file name. In other words, I will do this:

:echo Myfun("pattern")

and the result will be:

"scratch1" [Modified][New file] 3 lines --100%--   

If I use the message history (echom) it clearly shows that the correct result is being generated and returned, but the message is getting overwritten by the "modified" message. I don't understand this because the script does not modify anything. Why is the status line getting overwritten?

The effect seems to be caused by bufdo. A minimal example of Myfun is the following:

function! Myfun( pattern )
    let command = '%s/'.a:pattern.'//gen'
    let count_pattern = 0
    bufdo let count_pattern += str2nr( strpart( execute( command ), 1 ) )
    return count_pattern
endfunction

If the environment has only one open buffer then the echo command works correctly, but if there are more than one buffers open, then the status line is getting overwritten. In other words, what is happening is the following sequence of events:

1. function runs (switching buffers in the process)
2. function returns a number it calculated
3. echo command prints that number to the status line
4. Vim writes ""example" [New file] --No lines in buffer--" to status line

So, after the command is over Vim is updating the status line if the buffer was changed at any point when the command executed. I need to prevent this from happening to see the result.

Answer 1

Your problem comes from the fact that bufdo loads each buffer in the current window and then Vim will output in the command line (note: Note the statusline, that is a different area!) that it is editing the buffer and it has been modified.

I suppose, you have 'hidden' set, otherwise, you wouldn't be able to switch buffers.

BTW: the result of your function is printed correctly, it is just that afterwards the message area will get overwritten by another message.

The simplest way would be to use :sil :bufdo to hide those messages or you can set the 'shortmess' option to include the flag "F" (which suppresses this info entirely).

Note: Whenever you use the bufdo function, you should restore the current buffer afterwards again. It is a bad habit to find yourself in another buffer other executing a function. This might lead to unexpected results.