md() {
    exp=$(cat <<-EOF
<the content of your sed file>
...
EOF
)
   sed -E "$exp" file.md
}

bash: /{: No such file or directory
bash: x: command not found
bash: /^: No such file or directory
bash: /{: No such file or directory
bash: x: command not found
bash: b: command not found
bash: command substitution: line 4: syntax error near unexpected token `}'
bash: command substitution: line 4: `}'
bash: command substitution: line 2: syntax error near unexpected token `^'
bash: command substitution: line 2: `s/(^|[^\\'
bash: command substitution: line 2: syntax error: unexpected end of file
bash: command substitution: line 2: syntax error: unexpected end of file
bash: s/\t/  /g
< all other sed commands >
...
...
: bad substitution
# example

Paragraph.

- it
- works

## bye

$> printf "\`\`\`\narrow function => return\n\`\`\`" | ./md-to-html.sed
<pre><code>arrow function &amp;ge; return
</code></pre>