Like append() but append the text in buffer {buf}.

This function works only for loaded buffers. First call bufload() if needed.

For the use of {buf}, see bufname().

{lnum} is the line number to append below. Note that using line() would use the current buffer, not the one appending to. Use "$" to append at the end of the buffer. Other string values are not supported.

On success 0 is returned, on failure 1 is returned. In Vim9 script an error is given for an invalid {lnum}.

If {buf} is not a valid buffer or {lnum} is not valid, an error message is given. Example:

:let failed = appendbufline(13, 0, "# THE START")

However, when {text} is an empty list then no error is given for an invalid {lnum}, since {lnum} isn't actually used.

Can also be used as a method after a List, the base is passed as the second argument:

mylist->appendbufline(buf, lnum)