Replace all local images references in HTML with base64 inline data, e.g. for HTML emails

inline-images.sh

#!/bin/bash

# Searches for <img src="localImage" alt="altText"/> in index.html and replaces with:
# <img src="data:image/png;base64,..." alt="altText"/>
# writes output to build/index.html

mkdir -p build

# awk is really awkward: does not accept regexp groups :(
# I'll keep the () anyways for my mental health!

awk -F'"' -v q="'" '/<img src=\"(.*)\" alt=\".*\"\/>/ {
  cmd=sprintf("openssl enc -base64 -in \"%s\" | tr -d %c\\n%c",$2,q,q)
  cmd | getline b64
  close(cmd)
  $0=$1 "\"data:image/png;base64," b64 "\" alt=\"" $4 "\"/>"
}1' index.html >build/index.html

Inspired by https://stackoverflow.com/questions/5465446/replacing-all-images-in-a-css-file-with-base64-encoded-strings-from-the-command