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How do I grep OUT the content of a file from another file

Say I have a file "file1" and it has

a
b
c

and another file "file2" that has

a
b
c
d
e
f

I would usually do

cat file2 | grep -v a | grep -v b | grep -v c 

Is there a way to do this with the files

grep -v file2 file1
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2 Answers 2

up vote 5 down vote accepted

Use diff to find the differences and sed to select, format and print just the added lines:

diff file1 file2 | sed -n "/^>/{s/> //;p}"

Added:

If the files are in different orders, then sort them both first, then diff them.

sort file1 > file1.s
sort file2 > file2.s
diff file1.s file2.s | sed -n "/^>/{s/> //;p}"

If you're using bash, you can use <(...) process substitution:

diff <(sort file1) <(sort file2) | sed -n "/^>/{s/> //;p}"
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That's very clever. The problem is a bit under-specified though. What if the lines in the two files were in different orders? –  dangph Dec 9 '12 at 6:30

GNU grep (and I imagine others also) can take the -f option:

   -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.)

So, you could do this:

grep -vFf file1 file2 

Following Nicole Hamilton's suggestion in the comments, I have added the '-F' option which causes grep to interpret its PATTERN (in this case, each line in file1) as fixed strings and not regular expressions:

  -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.)

I have also written a PERL script with a few more options:

$ list_compare.pl -h

  USAGE: compare_lists.pl FILE1 FILE2

  This script will compare FILE1 and FILE2, searching for the 
  contents of FILE1 in FILE2 (and NOT vice-versa). FILE one must 
  be one search pattern per line, the search pattern need only be 
  contained within one of the lines of FILE2.

OPTIONS: 
  -c : Print patterns COMMON to both files
  -f : Search only the first characters (until the 1st space) of each line of 
       FILE2 for the search pattern given in FILE1. So, if FILE1 contains
       "foo bar", only "foo" will be taken as a pattern (MUCH faster).
  -d : Print duplicate entries     
  -m : Print patterns MISSING in FILE2 (default)
  -h : Print this help and exit
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1  
+1 The -f option is a pretty good idea. But you'll likely want to use fgrep not grep so the lines you read with -f will be treated as literal text, not regex patterns. –  Nicole Hamilton Dec 9 '12 at 17:06
    
@NicoleHamilton, and that just explained the weird behavior I have been getting over the years with grep -f and the reason I wrote that Perl script in the first place! Thanks, I had not realized that it was treating the file's lines as regexes. Changed the question to use grep -Ff (fgrep is depreciated says man grep). –  terdon Dec 9 '12 at 20:54

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