#!/bin/bash
# Minimalist implementations of the 'index' and 'rindex' functions in pure Bash
# returns a 0 based offset into your haystack string
# This is provided solely as-is, and all I ask is a one line thank you note
# with my email address.
# Written by Robin H. Johnson <robbat2@orbis-terrarum.net>

function index() {
local haystack="$1"
local needle="$2"
local fromstart="${3-0}"
haystack="${haystack:${fromstart}}"
local tmp="${haystack/${needle}*}"
[ "${#tmp}" -ge "${#haystack}" ] && echo -1 || echo $((${#tmp}+${fromstart}-1))
}

function rindex() {
local haystack="$1"
local needle="$2"
local fromend="${3-0}"
haystack="${haystack:0:$((${#haystack}-${fromend}+1))}"
local tmp="${haystack%${needle}*}"
[ "${#tmp}" -ge "${#haystack}" ] && echo -1 || echo $((${#tmp}-1))
}

# Testing code
HAYSTACK="Mary had a little lamb but the lamb had had measles"
NEEDLE="had"
echo "'${HAYSTACK}' (${#HAYSTACK})"
echo -n "Looking for needle '${NEEDLE}' [expect 4]: "
index "${HAYSTACK}" "${NEEDLE}" 
echo -n "Looking for needle '${NEEDLE}' after 7 [expect 35]: "
index "${HAYSTACK}" "${NEEDLE}" 7
echo -n "Looking for needle 'foo' [expect -1]: "
index "${HAYSTACK}" "foo"
echo -n "Looking for needle 'foo' after 7 [expect -1]: "
index "${HAYSTACK}" "foo" 7

echo -n "Looking for needle '${NEEDLE}' in reverse [expect 39]: "
rindex "${HAYSTACK}" "${NEEDLE}"
echo -n "Looking for needle '${NEEDLE}' in reverse skipping 10 [expect 35]: "
rindex "${HAYSTACK}" "${NEEDLE}" 10
echo -n "Looking for needle '${NEEDLE}' in reverse skipping 20 [expect 4]: "
rindex "${HAYSTACK}" "${NEEDLE}" 20
echo -n "Looking for needle 'foo' in reverse [expect -1]: "
rindex "${HAYSTACK}" "foo"
echo -n "Looking for needle 'foo' in reverse skipping 10 [expect -1]: "
rindex "${HAYSTACK}" "foo" 10