Shell Programming and Scripting

I have to compare two text files, very few of the lines in these files will have some difference in some column.
The files size is in GB.
Sample lines are as below:
11111122222222333333aaaaaaaaaabbbbbbbbbccccccccdddddd
11111122222222333333aaaaaaaaaabbbbbbbbbccccccccddeddd

So assuming these two lines are from file1 and file2 respectively, I should get the second file line in a new output file which is the difference file.

What I would like to do is read line1 from file1 and loop through all the lines in file2 and stop when a match is found, else print it that line to output file. And repeat the same steps for all the lines from file1.

Appreciate any help in this regard.

What do you mean by "stop when a match is found", then you read more from file1....
Do you want the line number? Stop usually means to exit the read loop.

Yes, I want to exit the read loop when a match is found, I do not want to check any more for that line.
No I do not need the line number.

If I understand what you're trying to do correctly, here's a quick bash script.

Code:

#!/bin/bash

compareFile = "/path/to/file/to/compare.txt"
outputFile = "/path/to/outputFile.txt"

for filename in /some/dir/of/text/files/*.txt; do 
        
        numlines=`cat $filename | wc -l`
                
        for i in `seq 1 $numlines`; do 
                current=`cat $filename | head -$i | tail -1` 
 
                grep -q "${current}" ${compareFile} 
 
                if [ $? != 0 ]; then
                         #doesn't exist, append to $outputFile
                        echo "${filename}:${current}" >> ${outputFile} 
                fi
        done 
done

Hi, Thank you for the quick solution and looks pretty much what I want.
But I am unable to run this script, I use ksh.
One of the errors is "seq: command not found"

which seq (usually resides in /usr/bin/)

It's an individual executable command; should be part of the coreutils package if you're using linux.

if it exists on your system, modify the script
seq="/path/to/seq"

then modify the for statement to use the variable: for i in `${seq}...

As mentioned by OP, the files are in GB. I think there will be some performance lag. just a guess.
Also seq is not a standard command in some *nix OS. Therefore if you want to use loops that loop over a counter, a while loop can be used instead. eg while [ $num -le $numlines ]