how to auto update file path in file header with autocmd in vi/vim?

I have a function in my .vimrc that automatically updates the file I'm currently editing with the timestamp (Modified) of the last 'save' (:w).

I would like to also update the Filename and Filepath. I have an autocmd that updates the filename (through expand("%"). As for the Filepath, from what I read in the documentation, using expand("%:p:h") should permit me to insert the path (excluding the filename), but it does not work.

Anybody can tell me how insert the Filepath in my header ?

Example of file header that I wish to update:

Modified: November 13 2016
Filename: myfile
Filepath: /home/me/path/tomyfile/

Code I have at the moment :

autocmd BufWritePre * call UpdHeader()

function! UpdHeader()   
  " update path <<<<<<  DOES NOT WORK  >>>>>>>
  silent! execute "1," . 10 .  "g/Filepath:.*/s//Filepath: " .expand("%:p:h")

  " update filename  <<WORKS>>
  silent! execute "1," . 10 .  "g/Filename:.*/s//Filename: " . expand("%")

  " update last mod date <<WORKS>>
  silent! execute "1," . 10 .  "g/Modified:.*/s//Modified: " . strftime("%d %B %Y%t%t%T (%z)%tBy : ") . $USER
  ...
endf

thx! M

Solution

You need to perform proper escaping on the filepath, as you use / both as a separator in :substitute, and the (Unix-style) replacement path also has / separators in it. :substitute would have alerted your via E488: Trailing characters, but you've :silent! it.

A quick fix would be switching of :substitute separators, hoping that # will never appear in a file path:

silent! execute "1," . 10 .  "g/Filepath:.*/s##Filepath: " .expand("%:p:h")

Better do proper escaping:

silent! execute "1," . 10 .  "g/Filepath:.*/s//Filepath: " .escape(expand("%:p:h"), '/\'. (&magic ? '&~' : ''))

Alternatively, you can replace with an expression:

silent! execute "1," . 10 .  "g/Filepath:.*/s//\\='Filepath: ' .expand('%:p:h')"

Your filename expansion would benefit from that as well.