#!/usr/bin/env bash

# note, unicode is passed as is (as it should be, imho)
# and forward slashes are not unnecessarily escaped
jsonesc () {
  local q="$1"
  q=${q//$'\\'/\\\\}    # back slash (must be first)
  q=${q//$'\"'/'\"'}    # double quote
  #q=${q//$'/'/'//'}    # forward slash (but just no)
  q=${q/$'\b'/'\b'}     # backspace
  q=${q//$'\f'/'\f'}    # form feed
  q=${q//$'\n'/'\n'}    # line feed
  q=${q//$'\r'/'\r'}    # carriage return
  q=${q/$'\t'/'\t'}     # tab
  printf '%s' $q
}

IFS=
read line
buf=$line
while IFS= read  line; do
  buf="${buf}"$'\n'"${line}"
done

jsonesc "${buf}"