Unix Diff

diff is a mightly command line tool found in most of Unix and Unix-like operating systems. diff helps you to find differences between files and directories.

Things You Can Do with Unix Diff

• Compare files with diff
• Compare directories with diff
• Compare binary files with diff
• Compare backup copies to current files

How To Use Unix Diff

In its simplest form, compares two text files – you provide their names as command line options.

Let’s create two files first:

greys@maverick:~ $ touch try
greys@maverick:~ $ touch try2

Diff won’t show any difference because they’re exactly the same – empty new files:

greys@maverick:~ $ diff try try2

If we change one of the files by adding the hello word to it, see what happens:

greys@maverick:~ $ echo "hello" >> try2
greys@maverick:~ $ diff try try2
0a1
> hello

Diff spotted the difference and indicated, which file has it (> means second file, the file in the right section of the command line).

Now, let’s add something else to the first file to make things a bit more interesting:

greys@maverick:~ $ echo "hi" >> try
greys@maverick:~ $ diff try ttry2
1c1
< hi
---
> hello

See? diff now highlighted that the first file (< pointing to the file in the left part of the command line you specified) also has a line that’s different from second file.

If we now add exactly the same line to both files, diff will ignore it because it only shows what’s different:

greys@maverick:~ $ echo "test" >> try
greys@maverick:~ $ echo "test" >> try2
greys@maverick:~ $ cat try
hi
test
greys@maverick:~ $ cat try2
hello
test
greys@maverick:~ $
greys@maverick:~ $ diff try try2
1c1
< hi
---
> hello

That’s it for today! I’ll show you some advanced usages of the diff command some other time.

See Also

• basic Unix commands
• Comparing text files with diff
• Unix Commands

See Also