bash - Docker number of lines in terminal changing inside docker

Question

I would like to know how to change the following behavior. Let's say my terminal has 28 lines. Then I use the following commands:

$ tput lines # my terminal
28
$ docker run  --rm  -it ubuntu:16.04 tput lines  # docker container
24  ## WHY??
$ docker run  --rm  -it ubuntu:16.04 bash # docker container inside command
root@810effa2777c:/# tput lines
28

As you can see, even when all the results should be 28, when I'm calling the container as docker run --rm -it ubuntu:16.04 tput lines it always gives me 24 despite the size of my terminal. This is not only with the ubuntu container, I also tried with debian (docker run --rm -it debian tput lines) and I'm having the same result 24.

The purpose of this is to use the mdp presentation tool which takes into account the lines in your terminal. When my implementation failed, I tried some other person's docker implementation but I ran to the same error.

Here's my error in an image:

Does anyone has any idea what it could be and how can this be solved?

Answer 1

UPDATE

you can now install goinside command line tool with:

sudo npm install -g goinside

and go inside a docker container with a proper terminal size with:

goinside docker_container_name

---

Logic behind goinside

thanks to @VonC answer we've got a solution for this problem with a simple bash snippet that we put in ~/.profile:

goinside(){
    docker exec -it $1 bash -c "stty cols $COLUMNS rows $LINES && bash";
}
export -f goinside

now you are able to get inside a docker container without terminal size issues with:

$ goinside containername

---

remember to source ~/.profile before using the goinside function.

---

enabling autocompletion in bash

(as it's shared in one of comments below) if you want to enable autocompletion for goinside you can use this snippet in .profile:

goinside(){
    docker exec -it $1 bash -c "stty cols $COLUMNS rows $LINES && bash";
}
_goinside(){
    COMPREPLY=( $(docker ps --format "{{.Names}}" -f name=$2) );
}
complete -F _goinside goinside;
export -f goinside;

---

enabling autocompletion in zsh

if you are using zsh as your default terminal you can use this snippet inside your ~/.zshrc file:

autoload bashcompinit
bashcompinit
goinside(){
    docker exec -it $1 bash -c "stty cols $COLUMNS rows $LINES && bash";
}
_goinside(){
    COMPREPLY=( $(docker ps --format "{{.Names}}" -f name=$2) );
}
complete -F _goinside goinside;
export goinside;