The command to post a comment looks like
post_comment username "your-permalink" "parent-post-account" "parent-permalink" "The Title" "The long-winded body." "" true
When you write the body, internal quotation marks (") must be "escaped", as well as escapes (\). Escaping a quotation mark looks like this \" and escaping an escape looks like this \\.
You make a new line with \n\n, that is, two escaped "n"s.