How to remove the lines which appear on file B from another file A?

Linux Problem Overview

I have a large file A (consisting of emails), one line for each mail. I also have another file B that contains another set of mails.

Which command would I use to remove all the addresses that appear in file B from the file A.

So, if file A contained:

A
B
C

and file B contained:

B    
D
E

Then file A should be left with:

A
C

Now I know this is a question that might have been asked more often, but I only found one command online that gave me an error with a bad delimiter.

Any help would be much appreciated! Somebody will surely come up with a clever one-liner, but I'm not the shell expert.

Linux Solutions

Solution 1 - Linux

If the files are sorted (they are in your example):

comm -23 file1 file2

-23 suppresses the lines that are in both files, or only in file 2. If the files are not sorted, pipe them through sort first...

See the man page here

Solution 2 - Linux

grep -Fvxf <lines-to-remove> <all-lines>

works on non-sorted files (unlike comm)
maintains the order
is POSIX

Example:

cat <<EOF > A
b
1
a
0
01
b
1
EOF

cat <<EOF > B
0
1
EOF

grep -Fvxf B A

Output:

b
a
01
b

Explanation:

-F: use literal strings instead of the default BRE
-x: only consider matches that match the entire line
-v: print non-matching
-f file: take patterns from the given file

This method is slower on pre-sorted files than other methods, since it is more general. If speed matters as well, see: https://stackoverflow.com/questions/18204904/fast-way-of-finding-lines-in-one-file-that-are-not-in-another

Here's a quick bash automation for in-line operation:

remove-lines() (
  remove_lines="$1"
  all_lines="$2"
  tmp_file="$(mktemp)"
  grep -Fvxf "$remove_lines" "$all_lines" > "$tmp_file"
  mv "$tmp_file" "$all_lines"
)

GitHub upstream.

usage:

remove-lines lines-to-remove remove-from-this-file

Solution 3 - Linux

awk to the rescue!

This solution doesn't require sorted inputs. You have to provide fileB first.

awk 'NR==FNR{a[$0];next} !($0 in a)' fileB fileA

returns

A
C

How does it work? > NR==FNR{a[$0];next} idiom is for storing the first file in an associative array as keys for a later "contains" test. > > NR==FNR is checking whether we're scanning the first file, where the global line counter (NR) equals to the current file line counter (FNR). > > a[$0] adds the current line to the associative array as key, note that this behaves like a set, where there won't be any duplicate values (keys) > > !($0 in a) we're now in the next file(s), in is a contains test, here it's checking whether current line is in the set we populated in the first step from the first file, ! negates the condition. What is missing here is the action, which by default is {print} and usually not written explicitly.

Note that this can now be used to remove blacklisted words.

$ awk '...' badwords allwords > goodwords

with a slight change it can clean multiple lists and create cleaned versions.

$ awk 'NR==FNR{a[$0];next} !($0 in a){print > FILENAME".clean"}' bad file1 file2 file3 ...

Solution 4 - Linux

Another way to do the same thing (also requires sorted input):

join -v 1 fileA fileB

In Bash, if the files are not pre-sorted:

join -v 1 <(sort fileA) <(sort fileB)

Solution 5 - Linux

You can do this unless your files are sorted

diff file-a file-b --new-line-format="" --old-line-format="%L" --unchanged-line-format="" > file-a

--new-line-format is for lines that are in file b but not in a --old-.. is for lines that are in file a but not in b --unchanged-.. is for lines that are in both. %L makes it so the line is printed exactly.

man diff

for more details

Solution 6 - Linux

This refinement of @karakfa's nice answer may be noticeably faster for very large files. As with that answer, neither file need be sorted, but speed is assured by virtue of awk's associative arrays. Only the lookup file is held in memory.

This formulation also allows for the possibility that only one particular field ($N) in the input file is to be used in the comparison.

# Print lines in the input unless the value in column $N
# appears in a lookup file, $LOOKUP;
# if $N is 0, then the entire line is used for comparison.

awk -v N=$N -v lookup="$LOOKUP" '
  BEGIN { while ( getline < lookup ) { dictionary[$0]=$0 } }
  !($N in dictionary) {print}'

(Another advantage of this approach is that it is easy to modify the comparison criterion, e.g. to trim leading and trailing white space.)

Solution 7 - Linux

You can use Python:

python -c '
lines_to_remove = set()
with open("file B", "r") as f:
    for line in f.readlines():
        lines_to_remove.add(line.strip())

with open("file A", "r") as f:
    for line in [line.strip() for line in f.readlines()]:
        if line not in lines_to_remove:
            print(line)
'

Solution 8 - Linux

You can use - diff fileA fileB | grep "^>" | cut -c3- > fileA

This will work for files that are not sorted as well.

Solution 9 - Linux

Just to add to the Python answer to the user above, here is a faster solution:

    python -c '
lines_to_remove = None
with open("partial file") as f:
    lines_to_remove = {line.rstrip() for line in f.readlines()}

remaining_lines = None
with open("full file") as f:
    remaining_lines = {line.rstrip() for line in f.readlines()} - lines_to_remove

with open("output file", "w") as f:
    for line in remaining_lines:
        f.write(line + "\n")
    '

Raising the power of set subtraction.

Solution 10 - Linux

To get the file after removing the lines which appears on another file

comm -23 <(sort bigFile.txt) <(sort smallfile.txt) > diff.txt

Solution 11 - Linux

To remove common lines between two files you can use grep, comm or join command.

> grep only works for small files. Use -v along with -f.

grep -vf file2 file1

This displays lines from file1 that do not match any line in file2.

> comm is a utility command that works on lexically sorted files. It > takes two files as input and produces three text columns as output: > lines only in the first file; lines only in the second file; and lines > in both files. You can suppress printing of any column by using -1, -2 > or -3 option accordingly.

comm -1 -3 file2 file1