> report_2019.org:
> 
> #+TITLE: Report 2019
> #+property: header-args :var year=2019
> 
> #+INCLUDE: "template.org" :lines "2-"
> 
> template.org:
> 
> #+TITLE: Report
> 
> * My headline
> 
> #+begin_src emacs-lisp :exports both :results value :eval yes
> year
> #+end_src
> 
> #+BEGIN_SRC bash
> ./get_log_file --start=$year-01-01 --end=$year-12-31
> #+END_SRC
> 
> #+BEGIN_SRC python
> log = pd.read_csv(f"log_{year}.csv")
> #+END_SRC

Thank you, I got it to work by only using

report_2019.org:

#+TITLE: Report 2019
#+property: header-args :var year=2019

#+INCLUDE: "template.org" :lines "2-"

template.org:

#+TITLE: Report

* My headline

#+BEGIN_SRC bash
./get_log_file --start=$year-01-01 --end=$year-12-31
#+END_SRC

#+BEGIN_SRC python
log = pd.read_csv(f"log_{year}.csv")
#+END_SRC