Helper script to ensure that Bash 4 and GNU tools are used on OS X

.00_README.md

This helper script can be sourced at the top of another Bash script to ensure that it runs under Bash 4 with GNU grep, readline, sed, and zcat.

It should be sourced in your script like this, before the part of the script that uses Bash 4 features or expects GNU tools:

source .ensure-bash4+gnu-tools.bash "$BASH_SOURCE" "$@"

.ensure-bash4+gnu-tools.bash

#!/bin/bash

set -e

SCRIPT="$(basename "$1")"

# Attempt to run under bash 4 if we aren't already
if [ "$BASH_VERSINFO" -lt 4 ]; then
	if [ `uname` = Darwin ]; then
		if brew info bash &> /dev/null; then
			exec "$(brew --prefix bash)/bin/bash" "$@"
		else
			echo >&2 <<-EOWARN
			ERROR: $SCRIPT requires bash 4+. You may use homebrew to install it:

				brew install bash
			EOWARN
			exit 1
		fi
	else
		echo >&2 <<-EOWARN
		ERROR: $SCRIPT requires Bash 4+
		EOWARN
		exit 1
	fi
fi

# From https://gist.github.com/bittner/5436f3dc011d43ab7551
# cross-OS compatibility (ggrep, greadlink, gsed, gzcat are GNU implementations for OS X)
if [ `uname` = Darwin ]; then
	if which ggrep greadlink gsed gzcat > /dev/null; then
		unset GREP_OPTIONS
		unalias grep readlink sed zcat &> /dev/null || true
		alias grep=ggrep readlink=greadlink sed=gsed zcat=gzcat
		shopt -s expand_aliases
	else
		echo >&2 <<-EOWARN
		ERROR: $SCRIPT requires GNU utils for Mac. You may use homebrew to install them:

			brew tap homebrew/dupes
			brew install coreutils gnu-sed homebrew/dupes/grep
		EOWARN
		exit 1
	fi
fi