hlines in bash/sh source code block

Question

How can I insert a horizontal line (hline) in a bash/sh source code block? My goal is to separate the header line from the rest.

#+begin_src sh
echo "header1,header2"
echo "???"  # placeholder for the magic value
echo "value1,value2"
echo "value1,value2"
#+end_src

The desired outcome would be

#+RESULTS:
| header1 | header2 |
|---------+---------|
| value1  | value2  |
| value1  | value2  |

In a Python src block I can insert a None-Value and get an hline. I hope there is a possibility.

Edit: @jagrg answers solves the problem to separate the header from the rest I would also to insert a hline at any point in the table. Here is the expected outcome.

#+begin_src bash :colnames '("header1" "header2")
echo "value1,value2"
echo "value1,value2"
echo "???" # magic value
echo "value1,value2"
#+end_src

#+RESULTS:
| header1 | header2 |
|---------+---------|
| value1  | value2  |
| value1  | value2  |
|---------+---------|
| value1  | value2  |

I tried echo hline and echo "hline" with no success. I also looked in the code of ob-shell.el and it looks that a simple echo hline should do it but it doesn't.

Answer 1

You can specify column names as header arguments (see here).

#+begin_src sh :colnames '("header1" "header2")
echo "value1,value2"
echo "value1,value2"
#+end_src

#+RESULTS:
| header1 | header2 |
|---------+---------|
| value1  | value2  |
| value1  | value2  |

To answer your second question, here's a solution you can try using sed (see this thread).

#+begin_src sh :results raw
(
echo "header,header2"
echo ","
echo "value1,value2"
echo "value1,value2"
echo ","
echo "value1,value2"
) | sed -re 's/^|,/|/g' -e 's/^\|$/|-/'
#+end_src

#+RESULTS:
| header | header2 |
|--------+---------|
| value1 | value2  |
| value1 | value2  |
|--------+---------|
| value1 | value2  |

Answer 2

If you don't want to rewrite your script to use raw output you also can use the :post parameter to do add hlines during post-processing. This can also be combined with :colnames. I.e.

#+name: add-footer
#+begin_src elisp :var table=""
(append (butlast table) '(hline) (last table))
#+end_src

#+name: add-hlines
#+begin_src elisp :var table="" :hlines yes :colnames true
(cl-map 'list
        (lambda (r) (if (and (listp r) (equal (car r) "hline"))
                        'hline
                      r))
        table)
#+end_src

Add a hline at a fixed position

#+begin_src bash :colnames '("header1" "header2") :post add-footer(*this*)
echo "value1,value2"
echo "value2,value3"
echo "value5,value4"
#+end_src

#+RESULTS:
| header1 | header2 |
|---------+---------|
| value1  | value2  |
| value2  | value3  |
|---------+---------|
| value5  | value4  |

Or use a 'hline' keyword for dynamic positions

#+begin_src bash :colnames '("header1" "header2") :post add-hlines(*this*)
echo "value1,value2"
echo "value3,value4"
echo "hline," # magic value
echo "value5,value6"
echo "value7,value8"
#+end_src

#+RESULTS:
| header1 | header2 |
|---------+---------|
| value1  | value2  |
| value3  | value4  |
|---------+---------|
| value5  | value6  |
| value7  | value8  |