md2tex.py

#!/usr/bin/env python3

# Render equations in $$...$$ or $...$ in markdown to svg
# Depend on command `tex2svg`
# To install: `sudo npm install -g mathjax-node-cli`

import sys

instr = sys.stdin.read()

instr = instr.replace("\\$", "\xfff0")

outstr = str()
l1 = instr.split("$$")

if len(l1) % 2 == 0:
	raise RuntimeError("error, $$ not paired")

def parseText(instr):
	l1 = instr.split("$")
	if len(l1) % 2 == 0:
		print(l1)
		raise RuntimeError("error, $ not paired")
	outstr = str()
	for i in range(len(l1)):
		if i % 2 == 0:
			outstr = outstr + l1[i]
		if i % 2 == 1:
			outstr = outstr + parseTexInline(l1[i])
	return outstr

import subprocess

def parseTexBlock(instr):
	ret = subprocess.check_output(['tex2svg', "--", instr.strip()])
	ret = ret.decode("utf-8")
	if len(ret) == 0:
		raise RuntimeError("invalid math: " + instr)
	ret = ret.replace("\n", "")
	ret = ret.replace("\r", "")
	ret = ret.strip()
	return ret

def parseTexInline(instr):
	ret = subprocess.check_output(['tex2svg', "--inline", "--", instr.strip()])
	ret = ret.decode("utf-8")
	if len(ret) == 0:
		raise RuntimeError("invalid math: " + instr)
	ret = ret.replace("\n", "")
	ret = ret.replace("\r", "")
	ret = ret.strip()
	return ret

for i in range(len(l1)):
	if i % 2 == 0:
		outstr = outstr + parseText(l1[i])
	if i % 2 == 1:
		outstr = outstr + parseTexBlock(l1[i])

outstr = outstr.replace('\xfff0', "$")

print(outstr)