diff and sdiff

diff can be used to compare differences between two files or two directories as well.

cat poem1
twinkle twinkle
oompa loompa

cat poem2
twinkle twinkle
little star
how I wonder
what you are.

diff poem1 poem2
2c2,4
< oompa loompa
---
> little star
> how I wonder
> what you are.

If we use the recursive option -r, just like we do with rm or find etc, we can compare content of the sub dir as well.

diff -r dir1 dir2
Only in dir1/dir11: testfile11
diff -r dir1/testfile1 dir2/testfile1
1,2d0
< this is a line in dir1 file test1
< this is another line in dir1/test1
Only in d1: t2

Without option -r

diff dir1 dir2
Common subdirectories: dir1/dir11 and dir2/dir11
diff dir1/testfile1 dir2/testfile1
1,2d0
< this is a line in dir1 file test1
< this is another line in dir1/test1
Only in d1: t2

For intensive file comparisons sdiff is better as it lets side by side comparison.

sdiff poem1 poem2
twinkle twinkle                    twinkle twinkle
oompa loompa                  |    little star
                             >    how I wonder
                             >    what you are.