Creating and applying patches in Linux

Anybody who has ever worked in software development would have many times come across the issue of updating or patching their projects to the latest version. In development environments this task is fairly easy if they are using version-ing systems like CVS, SVN, Visual Source Safe etc. But for a quick work around when no such infrastructure is in place is to use the simple linux command "diff".

For the purpose of demonstration we can create a directory structure that looks like a software project .

[safeer@LinuxBox tmp]$mkdir version1;cd version1
[safeer@LinuxBox tmp]$echo "File1version1" > file1;echo "File2version1" > file2
[safeer@LinuxBox tmp]$mkdir includes1;cd includes1
[safeer@LinuxBox tmp]$echo "Lib1version1" > lib1;echo "Lib2version1" > lib2

The project directory looks like this:

version1
|------includes1
| |-------lib1
| |-------lib2
|-------file1
|-------file2

Now I am going to update this project.

[safeer@LinuxBox tmp]$cp -r version1 version2

Whenever you update your project, keep a copy of the source project untouched and update only a fresh copy of that project.

Updating file1 & lib1
[safeer@LinuxBox tmp]$echo File1version2 >> file1;cd includes1;echo Lib2version2 >> lib2

Add new subdirectory and files to project
[safeer@LinuxBox tmp]$mkdir includes2;cd includes2;echo "Lib3version2" > lib3;echo "Lib4version2" > lib34

The updated project directory looks like this:

version2
|------includes1
| |-------lib1
| |-------lib2 ====> Updated
|------includes2 ====
| |-------lib3 ==== } Newly added
| |-------lib4 ====
|-------file1
|-------file2 ====> Updated

[safeer@LinuxBox tmp]$ls
veersion1 version2

Now create the patch file:

[safeer@LinuxBox tmp]$diff -Naur version1 version2 > version-1-2.patch
[safeer@LinuxBox tmp]$cat version-1-2.patch

diff -Naur version1/file1 version2/file1
--- version1/file1 2007-02-05 11:31:08.000000000 +0000
+++ version2/file1 2007-02-05 11:33:34.000000000 +0000

@@ -1 +1,2 @@
File1version1
+File1version2
diff -Naur version1/includes1/lib2 version2/includes1/lib2
--- version1/includes1/lib2 2007-02-05 11:32:20.000000000 +0000
+++ version2/includes1/lib2 2007-02-05 11:34:06.000000000 +0000
@@ -1 +1,2 @@
Lib2version1
+Lib2version2
diff -Naur version1/includes2/lib3 version2/includes2/lib3
--- version1/includes2/lib3 1970-01-01 00:00:00.000000000 +0000
+++ version2/includes2/lib3 2007-02-05 11:35:16.000000000 +0000
@@ -0,0 +1 @@
+Lib3version2
diff -Naur version1/includes2/lib4 version2/includes2/lib4
--- version1/includes2/lib4 1970-01-01 00:00:00.000000000 +0000
+++ version2/includes2/lib4 2007-02-05 11:35:22.000000000 +0000
@@ -0,0 +1 @@
+Lib4version2

Now suppose that our old project is installed in /usr/project/

[safeer@LinuxBox tmp]$cd /usr/project;ls
version1
Now copy the patch file to this directory
[safeer@LinuxBox tmp]$cp /home/safeer/tmp/version-1-2.patch .
Now apply the patch

[safeer@LinuxBox tmp]$patch -p0 < version-1-2.patch
patching file version1/file1
patching file version1/includes1/lib2
patching file version1/includes2/lib3
patching file version1/includes2/lib4

The patch has updated the modified files file1,lib2 and created new directory includes2 with two files lib3 and lib4 in it.
diff command can record the difference of not only text files, but executables also. So this will work for all sort of files