Shell Script To Write Odd and Even Line To Respective Files

#!/bin/bash
# Write a shell script that, given a file name as the argument will write
# the even numbered line to a file with name evenfile and odd numbered lines
# in a text file called oddfile.
# -------------------------------------------------------------------------
# Copyright (c) 2001 nixCraft project <http://cyberciti.biz/fb/>
# This script is licensed under GNU GPL version 2.0 or above
# -------------------------------------------------------------------------
# This script is part of nixCraft shell script collection (NSSC)
# Visit http://bash.cyberciti.biz/ for more information.
# -------------------------------------------------------------------------
 
file=$1
counter=0
 
eout="evenfile.$$" # even file name
oout="oddfile.$$" # odd file name
 
if [ $# -eq 0 ]
then
	echo "$(basename $0) file"
	exit 1
fi
 
if [ ! -f $file ]
then
	echo "$file not a file"
	exit 2
fi
 
while read line
do
	# find out odd or even line number
	isEvenNo=$( expr $counter % 2 )
 
	if [ $isEvenNo -ne 0 ]
	then
		# even match
		echo $line >> $eout
	else
		# odd match
		echo $line >> $oout
	fi
	# increase counter by 1
	(( counter ++ ))
done < $file
echo "Even file - $eout"
echo "Odd file - $oout"