Preventing the join() command from adding extra space

Question

I am trying to use the join command to join multiple strings. The join command seems to add one character of space in between each of the strings. But I don't want any space added.

As an example, I'm working on a function that finds the associated .pdf file of a .tex file. So if I'm editing the file /home/user/paper.tex, I would like to create the string /home/user/paper.pdf. My attempt is

join([expand('%:p:r'), '.pdf'])

which returns /home/user/paper .pdf

Answer 1

From :help join():

join({list} [, {sep}])

            [..]

            When {sep} is specified it is put in between the items.  If
            {sep} is omitted a single space is used.

            [..]

So the solution is to add an empty string in the second sep parameter:

:echo join([expand('%:p:r'), '.pdf'])
/usr/share/vim/vim81/doc/eval .pdf

:echo join([expand('%:p:r'), '.pdf'], '')
/usr/share/vim/vim81/doc/eval.pdf

In this case you don't really need to use join() by the way, and could just use:

:echo expand('%:p:r') . '.pdf'