Test for mutually exclusive options in shell scripts

test_mutually_exclusive.sh

#!/bin/sh
set -e

[ -z "$FIRST" -a -z "$SECOND" -a -z "$THRID" ] && { echo "FIRST, SECOND or THIRD arg must be specified"; exit 1; }

FIRST_ARG="${FIRST:-}"
SECOND_ARG="${SECOND:-}"
THIRD_ARG="${THIRD:-}"          

FINAL_ARG="${FIRST_ARG}${SECOND_ARG}${THIRD_ARG}"

[ $FINAL_ARG == "$FIRST_ARG" -o $FINAL_ARG == "$SECOND_ARG" -o $FINAL_ARG == "$THIRD_ARG" ] || { echo "FIRST, SECOND and THIRD are mutually exclusive"; exit 1; }

echo $FINAL_ARG