Shell Programming and Scripting

awk ' NR % 2 == 1 { oddline=$0; next } oddline != $0 { print "line " NR-1 " and line " NR " are different." }' inputfile

#!/bin/bash
while read A
do
    read B
    ((i+=2))
    [ "$A" != "$B" ] && echo "Lines $((i-1)) and $i are different"
done < inputfile

awk '{a=$0;b=NR;getline; if (a!=$0) printf "line %d and line %d are different", b,NR}' urfile

awk '{getline x; if(x!=$0) printf "lines %d and %d differ..\n",NR-1,NR}' infile

sed -n 'N;/\(..*\)\n\1/!{s/$/\nThe two lines above differ/p}' infile

while read A # read line and put in variable A. If unreadable (EOF) the break the loop.
do
    read B # read next line and put in variable B
    ((i+=2)) # increment variable i by 2 (like i=i+2)
    # [ "$A" != "$B" ] && echo "Lines $((i-1)) and $i are different"
    # can be written
    if [ "$A" != "$B" ] # if values of variables A and B are different ('[ ]' stands for 'test')
    then echo "Lines $((i-1)) and $i are different" # OK ?
    fi
done < inputfile # tells the loop to read from inputfile (else, it would read from keyboard.)