#!/bin/bash

#
# Three word regular expression
#
re='^([a-zA-Z]+) +([a-zA-Z]+) +([a-zA-Z]+) *\.?'

#
# A sentence is expected as the only argument
#
if [[ $# -ne 1 ]]; then
    echo "Usage: $0 sentence"
    exit 1
fi

echo "Sentence: $1"
if [[ $1 =~ $re ]]; then
    echo "Matched"
    for i in {0..3}; do
        printf '%2d %s\n' $i "${BASH_REMATCH[$i]}"
    done
fi