How can I show lines in common (reverse diff)?

user_14420 0
Viewed 121285

I have a series of text files for which I'd like to know the lines in common rather than the lines which are different between them. Command line Unix or Windows is fine.

File foo:

linux-vdso.so.1 =>  (0x00007fffccffe000)
libvlc.so.2 => /usr/lib/libvlc.so.2 (0x00007f0dc4b0b000)
libvlccore.so.0 => /usr/lib/libvlccore.so.0 (0x00007f0dc483f000)
libc.so.6 => /lib/libc.so.6 (0x00007f0dc44cd000)

File bar:

libkdeui.so.5 => /usr/lib/libkdeui.so.5 (0x00007f716ae22000)
libkio.so.5 => /usr/lib/libkio.so.5 (0x00007f716a96d000)
linux-vdso.so.1 =>  (0x00007fffccffe000)

So, given these two files above, the output of the desired utility would be akin to file1:line_number, file2:line_number == matching text (just a suggestion; I really don't care what the syntax is):

foo:1, bar:3 == linux-vdso.so.1 =>  (0x00007fffccffe000)
diff command-line
8 Answers

On *nix, you can use comm. The answer to the question is:

comm -1 -2 file1.sorted file2.sorted 
# where file1 and file2 are sorted and piped into *.sorted

Here's the full usage of comm:

comm [-1] [-2] [-3 ] file1 file2
-1 Suppress the output column of lines unique to file1.
-2 Suppress the output column of lines unique to file2.
-3 Suppress the output column of lines duplicated in file1 and file2.

Also note that it is important to sort the files before using comm, as mentioned in the man pages.

Daniel_Lew_602610
user_811790

I think diff utility itself, using its unified (-U) option, can be used to achieve effect. Because the first column of output of diff marks whether the line is an addition, or deletion, we can look for lines that haven't changed.

diff -U1000 file_1 file_2 | grep '^ '

The number 1000 is chosen arbitrarily, big enough to be larger than any single hunk of diff output.

Here's the full, foolproof set of commands:

f1="file_1"
f2="file_2"

lc1=$(wc -l "$f1" | cut -f1 -d' ')
lc2=$(wc -l "$f2" | cut -f1 -d' ')
lcmax=$(( lc1 > lc2 ? lc1 : lc2 ))

diff -U$lcmax "$f1" "$f2" | grep '^ ' | less

# Alternatively, use this grep to ignore the lines starting
# with +, -, and @ signs.
#   grep -vE '^[+@-]'

If you want to include the lines that are just moved around, you can sort the input before diffing, like so:

f1="file_1"
f2="file_2"

lc1=$(wc -l "$f1" | cut -f1 -d' ')
lc2=$(wc -l "$f2" | cut -f1 -d' ')
lcmax=$(( lc1 > lc2 ? lc1 : lc2 ))

diff -U$lcmax <(sort "$f1") <(sort "$f2") | grep '^ ' | less
user_3827000

In Windows, you can use a PowerShell script with CompareObject:

compare-object -IncludeEqual -ExcludeDifferent -PassThru (get-content A.txt) (get-content B.txt)> MATCHING.txt | Out-Null #Find Matching Lines

CompareObject:

  • IncludeEqual without -ExcludeDifferent: Everything
  • ExcludeDifferent without -IncludeEqual: Nothing
user_32036910
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