China DOS Union

Is there anyone who knows how to delete all duplicate lines in a text file and leave only non-duplicate lines? For example:
A text file contains the following lines:
a
a
b
c
d
Now I want to delete the duplicate a and leave only the non-duplicate b c d. Can this be done with a batch script?

Thank you everyone!

cd.>dst.txt&&for /f "delims=" %i in (src.txt) do findstr /b /e "%i" dst.txt||echo %i>>dst.txt

What is the use of this sentence "cd.>dst.txt"?

I am worried that the first time during the find process may not execute normally

Um, then I understand..

Actually, it didn't meet the owner's requirement. I just understand what the owner's requirement is at this moment

Hehe, using two for loops is the best way to handle this.

The building owner wants to delete all duplicate lines, not keep any.

Excuse me, how to use it? For this problem, my head has been messed up these two days.

『Building 9』:

Excuse me, brother on floor 7, how to use it? For this problem, my head has been messed up these two days, and also thank everest79 for the enthusiastic help!

My this can only delete the repeated lines

a
a
b
c
d

a
b
c
d
can't
a
a
b
c
d

b
c
d
src.txt is your original text, after execution, dst.txt is the filtered text, switch the cmd to the directory where src.txt is saved, then execute the above line

版主以前写过一个完全符合楼主要求的代码，搜下吧。
The moderator namejm once wrote a code that completely meets the requirements of the post, just search for it.

In addition, I ran the command from the brother on the second floor, and it was also a duplicate and couldn't be deleted. After running, it was still
a
a
b
c
d

Think carefully, I tried it, it's okay, let's see if there's any mistake.

Then defining an .ini file can meet the requirement.

The .ini file contains the things to be deleted.

Then there are still two for loops.