Compare two files in linux and output the result in one of the files-CodePudding

I have two files

file1.txt

  a
  b
  c

file2.txt

  a
  b
  c
  d

Now using grep command

grep -vf file1.txt file2.txt

will give me output as ->

But using this I can't save this result in any one of files file1 or file2. I want to simply overwrite this result in any one of the files. How can this be done using grep?

CodePudding user response：

But using this I cant save this result in any one of files file1 or file2. I want to simply overwrite this result in any one of the files. How can this be done using grep

you can redirect the output to a file like this:

grep -vf file1.txt file2.txt > tmp_file && mv tmp_file file1.txt

Notice that with grep you cannot use the same input file as output file. To solve this you create a temporary file and then rename it to file1(2).txt

CodePudding user response：

If sed is an option, you can delete the matches within a loop and save in place

while IFS= read -r line; do
    sed -i "/$line/d" file2.txt
done < file1.txt

Output

$ cat file2.txt
d