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

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Top 5 Answer for linux - How to remove the lines which appear on file B from another file A?

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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

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


cat <<EOF > A b 1 a 0 01 b 1 EOF  cat <<EOF > B 0 1 EOF  grep -Fvxf B A 


b a 01 b 


  • -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: 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.


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

See also:

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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 


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 ... 
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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) 
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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

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