slackready — convert markdown on stdin to Slack mrkdwn on stdout. Usage: pbpaste | slackready | pbcopy

slackready

#!/usr/bin/env python3
"""Convert markdown on stdin to Slack mrkdwn on stdout.

Slack flavor:
  *bold*         (single asterisk, not double)
  _italic_       (underscore)
  ~strike~       (single tilde)
  <url|label>    (links)
  `code`         (same)
  ```code```     (same)
  > quote        (same)
  - bullet       (same)
  # Heading      (not supported -- degrades to *Heading*)

Pipe usage:
  pbpaste | slackready | pbcopy
  cat notes.md | slackready
"""
import re
import sys


def convert(text: str) -> str:
    stash: list[str] = []

    def park(m: re.Match) -> str:
        stash.append(m.group(0))
        return f"\x00CODE{len(stash) - 1}\x00"

    text = re.sub(r"```[\s\S]*?```", park, text)
    text = re.sub(r"`[^`\n]+`", park, text)

    text = re.sub(r"(?<!\*)\*([^*\n]+?)\*(?!\*)", r"_\1_", text)

    def header(m: re.Match) -> str:
        inner = re.sub(r"\*\*([^*]+)\*\*", r"\1", m.group(1).strip())
        inner = re.sub(r"__([^_]+)__", r"\1", inner)
        return f"*{inner}*"

    text = re.sub(r"^#{1,6}[ \t]+(.+?)[ \t]*#*[ \t]*$", header, text, flags=re.MULTILINE)

    text = re.sub(r"\*\*([^*\n]+?)\*\*", r"*\1*", text)
    text = re.sub(r"__([^_\n]+?)__", r"*\1*", text)
    text = re.sub(r"~~([^~\n]+?)~~", r"~\1~", text)
    text = re.sub(r"\[([^\]\n]+)\]\(([^)\s]+)\)", r"<\2|\1>", text)
    text = re.sub(r"^[ \t]*(?:-{3,}|\*{3,}|_{3,})[ \t]*$", "", text, flags=re.MULTILINE)

    return re.sub(r"\x00CODE(\d+)\x00", lambda m: stash[int(m.group(1))], text)


if __name__ == "__main__":
    if len(sys.argv) > 1 and sys.argv[1] in ("-h", "--help"):
        print(__doc__)
        sys.exit(0)
    sys.stdout.write(convert(sys.stdin.read()))