I use YouCompleteMe for python3 code completion, and when I have

let g:ycm_python_binary_path = '/usr/bin/python3'

in my ~/.vimrc it works great. However, if I change it to

let python3path = system('/usr/bin/which python3')
let g:ycm_python_binary_path = python3path

It stops working. In both cases after vim startup the :echo g:ycm_python_binary_path shows /usr/bin/python3

What am I doing wrong?

1 Answer 1


Almost all Unix commandline programs end their output with a trailing newline, and Vim's system() doesn't remove this.

This can be a difficult to spot with a regular :echo; the easiest way to check this from Vim is by piping the output to hexdump:

:echo system('/usr/bin/which python3 | hexdump -C')
00000000  2f 75 73 72 2f 62 69 6e  2f 70 79 74 68 6f 6e 33  |/usr/bin/python3|
00000010  0a                                                |.|

The last character (0a) is a newline ("\n").

There is no straight-forward way to dump the hex output of a Vim string like with hexdump; so if you want to check the value of a string then the easiest way is to output with a prefix and suffix; for example:

:let python3path = system('/usr/bin/which python3')
:echo 'X' . python3path . 'X'

Notice how that second X is on a new line?

You can use something like this to remove the newline python3path:

:let python3path = system('/usr/bin/which python3')[:-2]
:echo 'X' . python3path . 'X'

which removes the last character (the \n) from the string that system() returns.

you could substitute() it, which is guaranteed to work for strings that don't end with a \n at a (very) slight performance/readability cost:

:let python3path = substitute(system('/usr/bin/which python3'), "\n$", "", 0)

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