Script to Compare two files line by line

Here is a script to compare two files line by line. The script compares two files that are given as input on the command line and outputs only the lines that are different between the two files .
It sure is not the most optimal script, but it works :-)

For eg let us take these two files
file1:

123
456
789

file2:
123
456
432


Save the above script as compare.sh and give execute permission to the script

$ chmod +x compare.sh

Run the script as follows.

$ ./compare.sh file1 file2
output :
Differing lines are
789
432

*****************************************compare.sh*******************
#!/bin/bash
if [ $# -ne 2 ]; then
    echo " Usage compare fil1 file2"
    exit
fi
      

i=0
while read line1
do
        flag=1
   while read line2
   do

    if [ "$line1" == "$line2" ];  then
        flag=0
        fi

   done < $2
        if [ $flag -eq 1 ]; then
             lines[i]=$line1
        ((i++))
    fi
done < $1

while read line1
do
        flag=1
   while read line2
   do

    if [ "$line1" == "$line2" ];  then
        flag=0
        fi

   done < $1
        if [ $flag -eq 1 ]; then
             lines[i]=$line1
         ((i++))
    fi
done < $2

echo "Differing lines are"
for((j=0;j<i;j++))
do
echo ${lines[j]}
done

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