Shell Script To Count English Language Articles Such As 'A', 'An' and 'The'

#!/bin/bash
# Write a shell script that counts English language articles (a, an, the) 
# in a given text file.
#
# --------------------------------------------------------------------
# This is a free shell script under GNU GPL version 2.0 or above
# Copyright (C) 2005 nixCraft project.
# Feedback/comment/suggestions : http://cyberciti.biz/fb/
# -------------------------------------------------------------------------
# This script is part of nixCraft shell script collection (NSSC)
# Visit http://bash.cyberciti.biz/ for more information.
# -------------------------------------------------------------------------
echo -n "Enter a file name : "
read file
a=0
the=0
an=0
 
# make sure file exist
if  [ ! -f $file ]
then
	echo "$file not a file!"
	exit 1
fi
 
# put while loop to read a $file
while read line
do
       #process each word 
	for w in $line 
	do
		# convert word to lowercase; so that we can count ThE, THE, the, THe etc all
		lword="$(echo $w | tr '[A-Z]' '[a-z]')"
 
		# is it 'a' article?
		[ $lword = "a" ] && (( a++ )) || :
		[ $lword = "the" ] && (( the++ )) || :
		[ $lword = "an" ] && (( an++ )) || :
	done
done < $file
 
# display stats
echo "a article occured $a times"
echo "the article occured $the times"
echo "an article occured $an times"