Delete lines from file A that is in file B

Question

I have two large files A and B

I need to delete lines that appear in file B from file A and save the result

to file C

I have tried comm -23 file1

Answer 1

As you mentioned, since comm needs sorted file to fetch the diff you can do in-line sorting before using comm like this :

comm -23 <(sort file1) <(sort file2) > fileC

Answer 2

You can use the following:

grep -vxFf fileB fileA > fileC

Sample:

$ seq 5 > a   # 1 to 5  in file a
$ seq 10 > b  # 1 to 10 in file b
$ grep -vxFf a b > c
$ cat c
6
7
8
9

From man grep

-F, --fixed-strings

Interpret PATTERN as a list of fixed strings, separated by newlines, any of which is to be matched. (-F is specified by POSIX.)

-f FILE, --file=FILE

Obtain patterns from FILE, one per line. The empty file contains zero patterns, and therefore matches nothing. (-f is specified by POSIX.)

-v, --invert-match

Invert the sense of matching, to select non-matching lines. (-v is specified by POSIX.)

-x, --line-regexp

Select only those matches that exactly match the whole line. (-x is specified by POSIX.)