backup Homebrew packages. See http://www.topbug.net/blog/2013/12/07/back-up-homebrew-packages/

backup-homebrew.sh

#!/bin/bash

brew_command=/usr/local/bin/brew
brew_cask_command="$brew_command cask"

echo '#!/bin/bash'
echo ''
echo 'trap ctrl_c INT'
echo 'function ctrl_c() {'
echo 'echo "** Trapped CTRL-C"'
echo 'exit 1'
echo '}'
echo ''
echo 'brew_command=/usr/local/bin/brew'
echo 'brew_cask_command="$brew_command cask"'
echo 'failed_items=""'
echo 'function install_package() {'
echo 'echo EXECUTING: brew install $1 $2'
echo '$brew_command install $1 $2'
echo '[ $? -ne 0 ] && $failed_items="$failed_items $1"  # package failed to install.'
echo '}'
echo 'function install_cask_package() {'
echo 'echo EXECUTING: brew cask install $1'
echo '$brew_cask_command install $1'
echo '[ $? -ne 0 ] && $failed_items="$failed_items $1"  # package failed to install.'
echo '}'

$brew_command tap | while read tap; do echo "$brew_command tap $tap"; done

$brew_command list | while read item;
do
  echo "install_package $item '$($brew_command info $item | /usr/bin/grep 'Built from source with:' | /usr/bin/sed 's/^[ \t]*Built from source with:/ /g; s/\,/ /g')'"
done

$brew_cask_command list | while read item;
do
  echo "install_cask_package $item"
done

echo '[ ! -z $failed_items ] && echo The following items were failed to install: && echo $failed_items'

crontab

0 */6 * * * ~/Dropbox/Apps/Homebrew/backup-homebrew.sh > ~/Dropbox/Apps/Homebrew/restore-homebrew.sh

restore-homebrew.sh

#!/bin/bash

trap ctrl_c INT
function ctrl_c() {
echo "** Trapped CTRL-C"
exit 1
}

brew_command=/usr/local/bin/brew
brew_cask_command="$brew_command cask"
failed_items=""
function install_package() {
echo EXECUTING: brew install $1 $2
$brew_command install $1 $2
[ $? -ne 0 ] && $failed_items="$failed_items $1"  # package failed to install.
}
function install_cask_package() {
echo EXECUTING: brew cask install $1
$brew_cask_command install $1
[ $? -ne 0 ] && $failed_items="$failed_items $1"  # package failed to install.
}
/usr/local/bin/brew tap caskroom/cask
/usr/local/bin/brew tap caskroom/versions
/usr/local/bin/brew tap ethereum/ethereum
/usr/local/bin/brew tap homebrew/core
/usr/local/bin/brew tap homebrew/dupes
/usr/local/bin/brew tap homebrew/fuse
/usr/local/bin/brew tap homebrew/science
/usr/local/bin/brew tap homebrew/services
/usr/local/bin/brew tap homebrew/versions
install_package aircrack-ng ''
install_package autoconf ''
install_package automake ''
install_package avrdude ''
install_package awscli ''
install_package boost ''
install_package c-ares ''
install_package cask ''
install_package cmake ''
install_package coreutils ''
install_package diff-so-fancy ''
install_package dirmngr ''
install_package docker ''
install_package docker-compose ''
install_package docker-machine ''
install_package e2fsprogs ''
install_package eigen ''
install_package elixir ''
install_package emacs ''
install_package encfs ''
install_package erlang ''
install_package ethereum ''
install_package ext2fuse ''
install_package ffmpeg ''
install_package fig ''
install_package freetype ''
install_package gdbm ''
install_package gettext ''
install_package gifsicle ''
install_package git ''
install_package gmp ''
install_package gnu-tar ''
install_package gnupg2 ''
install_package go ''
install_package gpg-agent ''
install_package gpm ''
install_package grep ''
install_package ilmbase ''
install_package imagemagick ''
install_package intltool ''
install_package ipfs ''
install_package jpeg ''
install_package jq ''
install_package keybase ''
install_package lame ''
install_package leptonica ''
install_package libassuan ''
install_package libelf ''
install_package libevent ''
install_package libftdi0 ''
install_package libgcrypt ''
install_package libgpg-error ''
install_package libksba ''
install_package libpng ''
install_package libtiff ''
install_package libtool ''
install_package libusb ''
install_package libusb-compat ''
install_package libvo-aacenc ''
install_package libwebsockets ''
install_package libyaml ''
install_package mackup ''
install_package makedepend ''
install_package mercurial ''
install_package mongodb ''
install_package mtr ''
install_package node ''
install_package ntfs-3g ''
install_package oniguruma ''
install_package openexr ''
install_package openssl ''
install_package pcre ''
install_package phantomjs ''
install_package pinentry ''
install_package pkg-config ''
install_package pngquant ''
install_package postgresql ''
install_package prettyping ''
install_package pth ''
install_package pup ''
install_package pv ''
install_package pypy ''
install_package python ''
install_package python3 ''
install_package qt ''
install_package rbenv ''
install_package readline ''
install_package reattach-to-user-namespace ''
install_package redis ''
install_package rlog ''
install_package ruby-build ''
install_package sqlite ''
install_package syncthing ''
install_package tbb ''
install_package tmux ''
install_package unixodbc ''
install_package vim '  --override-system-vi
  --override-system-vi'
install_package watch ''
install_package wget ''
install_package wxmac ''
install_package x264 ''
install_package xvid ''
install_package xz ''
install_package youtube-dl ''
install_cask_package alfred
install_cask_package atom
install_cask_package bartender
install_cask_package bitbar
install_cask_package brave
install_cask_package dayone-cli
install_cask_package handbrake
install_cask_package hazel
install_cask_package heroku-toolbelt
install_cask_package istat-menus
install_cask_package iterm2-beta
install_cask_package java
install_cask_package kaleidoscope
install_cask_package kicad-library (!)
install_cask_package kicad-nightly
install_cask_package launchcontrol
install_cask_package mono-mdk
install_cask_package osxfuse
install_cask_package virtualbox
install_cask_package wireshark
install_cask_package yujitach-menumeters
[ ! -z $failed_items ] && echo The following items were failed to install: && echo $failed_items

If you use Homebrew, use this script to backup your installed packages -- including cask packages! This makes setup on a new machine super fast.

1. Copy backup-homebrew.sh to your computer and make it executable. Don't copy restore-homebrew.sh. That's just an example of the restore file that you'll create.
2. Use crontab -e to schedule the script to run regularly. I run it every 6 hours. See my crontab entry above for an example. It overwrites restore-homebrew.sh every time it runs with a list of all your currently installed homebrew packages.
3. When you need to restore your homebrew installs, make your generated restore-homebrew.sh executable and execute it. All of your homebrew and homebrew cask packages will be automagically installed!

Bonus: If you use Dropbox, put the script and its output file in a Dropbox folder (see my crontab entry for an example of where I store the files) so you have it backed up should your hard drive die or computer go missing.

This is great, thanks for sharing! Do you know if Homebrew has some sort of native support for backing up the taps and formulas (or are they planning to add that feature)?

Any guidance on how to modify the script to pull out package options now that the "Built from source with:" has been changed to "Built from source on (date) at (time) with:"?