$ docker-compose run --rm web ruby -v
Starting mastodon_redis_1 ... done
Starting mastodon_db_1 ... done
Creating mastodon user (UID : 991 and GID : 991)...
Updating permissions...
Executing process...
ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-linux-musl]
$ ruby -v
ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-linux]
Dockerの内外で使ってるruby違うんだね