how to check for specific string in a file named abc.txt and write that missing string to another file (xyz.txt) using a shell script?

Question

For example, generally I need to check for 5 strings. (Note : the strings are in file format .txt)

1. file1.txt
2. file2.txt
3. file3.txt
4. file4.txt
5. file5.txt

but there are 3 strings in abc.txt

1. file1.txt
2. file2.txt
3. file3.txt

I wanted to check for specific strings in that abc.txt file and write the missing strings to xyz.txt file using a shell script.

example :-

1. file1.txt, file2.txt, file3.txt already exists in abc.txt --> so, it should leave or print any message like mentioned string exists

2. file4.txt, file5.txt does not exists in abc.txt --> so, when I check for these 2 strings, it should print a message specified file does not exits and it should write that missing string to xyz.txt file

example:- Input:- file/script/abc.txt abc.txt contains the following file1.txt file2.txt file3.txt

output:- file/script/xyz.txt xyz.txt should contain the following file4.txt file5.txt

Please note:- file4 and file5 are missing files in abc.txt

I have used the below code:-

Could anyone please help me as soon as possible.

Thanks in advance

Answer 1

$ comm -23 <(sort -u file1.txt) <(sort -u file2.txt) > linesUniqueToFile1.txt