Text Processing – Print Odd and Even Numbered Lines with Sed and Awk

I want to print the odd-numbered and even-numbered lines from files.

I found this shell script which makes use of echo.

#!/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"

But isn't there a way to do it in one line?

Yes, use awk, I read.

Even-numbered lines:

awk 'NR % 2' filename

odd-numbered lines:

awk 'NR % 2 == 1' filename

But it doesn't work for me. Both produce the same output, according to diff. When compared to the original file, they are both indeed half as long, and they both contain the odd-numbered lines. Am I doing something wrong?