Command Line – Output Common Lines of Two Text Files

command linediff()shell

Diff is a great tool to display the changes between two files. But how to display the similarities of two text files (while ignoring the differences)?

I.e. sample input:

a:
Foo Bar
X
Hello
World
42

b:
Foo Baz
Hello
World
23

Pseudo output (something like this):

@@ 2,3
=Hello World

Just sorting both files and using comm is not enough, because in that case the line information is lost.

Best Answer

How about using diff, even though you don't want a diff? Try this:

diff --unchanged-group-format='@@ %dn,%df 
  %<' --old-group-format='' --new-group-format='' \
  --changed-group-format='' a.txt b.txt

Here is what I get with your sample data:

$ cat a.txt 
Foo Bar
X
Hello
World
42
$ cat b.txt 
Foo Baz
Hello
World
23
$ diff --unchanged-group-format='@@ %dn,%df
%<' --old-group-format='' --new-group-format='' \
  --changed-group-format='' a.txt b.txt
@@ 2,3
Hello
World

Related Solutions

Shell – Diff Output of Two awk Commands

diff expects the names of two files, so you should put the two output on two files, then compare them:

awk '{print $3}' f1.txt | sort -u > out1
awk '{print $2}' f2.txt | sort -u > out2
diff out1 out2

or, using ksh93, bash or zsh, you can use process substitution:

diff <(awk '{print $3}' f1.txt | sort -u) <(awk '{print $2}' f2.txt | sort -u)

Diff Command – Why It Reports Two Files Differ When They Are the Same

Odd .. can you try cmp? You may want to use the '-b' option too.

cmp man page - Compare two files byte by byte.

This is one of the nice things about Unix/Linux .. so many tools :)

Best Answer

Related Solutions

Shell – Diff Output of Two awk Commands

Diff Command – Why It Reports Two Files Differ When They Are the Same

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