Re: Markdown format output for psql, design notes

Hi all,

# What I'd like to do
I've been working on the idea of a markdown format for psql as I had said in that thread : https://www.postgresql.org/message-id/flat/CAB_COdiiwTmBcrmjXWCKiqkcPgf_bLodrUyb4GYE6pfKeoK2eg%40mail.gmail.com

An attempt was made a year ago (see here : https://www.postgresql.org/message-id/flat/CAAYBy8bs%3D8vz6Ps_nLW24NJhqcxz4bsWBLawAiwWSPSLdWSmvA%40mail.gmail.com#eb7b6eb6daa60aac1f5fa001f934f89a), but didn't end up with something commitable.

What's more, I quite disagree with `\pset linestyle markdown` option to have a markdown output in psql, I prefer `\pset format markdown`.

# Some official doc about markdown So here are my thoughts (before writing any code) :

1. "Official" markdown seems to be the daring fireball project (see Aaron Schwartz's note here http://www.aaronsw.com/weblog/001189)
2. Official markdown doesn't support table formatting. Authors said we could just use HTML inside markdown to do so (it's quite not readable for a human, that's why I don't like this option) -> see here: https://daringfireball.net/projects/markdown/syntax#html
3. Table markdown is introduced in "Markdown Extra" that was first implemented in PHP (see here https://michelf.ca/projects/php-markdown/extra/#table)
4. I want to make the patch as simple as possible, so I won't implement cell alignment

# The result I want

From points 3 and 4, here is what I'd like to see :

| Header 1 | Header 2 | Header 3 |

|----------|----------|----------|

| content | content | content |

| content | content | content |

(2 rows)

**'|' at beginning and end of line are optional in markdown extra, but it seems as a consensus to always add them. You may challenge this choice, I'm open to discussion.**

From the fireball project (https://daringfireball.net/projects/markdown/syntax#backslash) and markdown extra (https://michelf.ca/projects/php-markdown/extra/#backslash), it seems we need to backslash escape all of those characters:

~~~

\   backslash

`   backtick

*   asterisk

_   underscore

{}  curly braces

[]  square brackets

()  parentheses

#   hash mark

+   plus sign

-   minus sign (hyphen)

.   dot

!   exclamation mark

:   colon

|   pipe

~~~

# psql syntax to get that

It feels to me that we should use the `\pset format` (or `-P` or `--pset=` in batch mode) syntax to tell psql we want markdown. So any of that one should provide a markdown output :

• `psql -P format=markdown`
• `psql --pset=format=markdown`
• `\pset format markdown` (in psql prompt command)

# Code to change

If I want to code that patch, here are the files I think I'll need to change :

• Documentation
  • doc/src/sgml/rel/psql-ref.sgml
  • src/bin/psql/help.c
• Tests
  • src/test/regress/expected/psql.out
  • src/test/regress/sql/psql.sql
• Code
  • src/bin/psql/command.c
  • src/bin/psql/tab-complete.c
    

**You're welcome to add any other file that I missed in that list!**

# What I'd like you to do

First, thanks to have read that whole mail and sorry I didn't mean to make it so long...

Then I'd like to know **what you think about what I'm about to do** before heading in a wrong direction.

Have a nice day,

Lætitia

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