Creating a Patch - a simple demonstration

Given below is a simple demostration of creating a patch for a file .

Follow the following steps :

1. Create 2 folders my_copy and upstream in the same directory.

   abhinav@abhinav-SVE15137CXW:~/homework/linuxibm$ ls -l total 8 drwxr-xr-x 2 abhinav abhinav 4096 Feb 14 13:55 my_copy drwxr-xr-x 2 abhinav abhinav 4096 Feb 14 13:48 upstream

xyz

1. Create a simple .c file named hello.c in upstream

   abhinav@abhinav-SVE15137CXW:~/homework/linuxibm/upstream$ cat hello.c #include int main(){ printf("Hello World"); return 0; }

2. copy upstream’s file hello.c into my_copy folder

   abhinav@abhinav-SVE15137CXW:~/homework/linuxibm/my_copy$ cp ../upstream/hello.c .

   \ the last ‘ . ‘ represents the current folder

3. Create a copy of this hello.c in hello_org.c abhinav@abhinav-SVE15137CXW:~/homework/linuxibm/my_copy$ cp hello.c hello_org.c

4. Make changes to the hello.c in the my_copy say , change “Hello World” to “Hello SASTRA” NOTE : Change in the hello.c in my_copy directory abhinav@abhinav-SVE15137CXW:~/homework/linuxibm/my_copy$ cat hello.c #include int main(){ printf("Hello SASTRA"); return 0; }
5. Let us see both the files abhinav@abhinav-SVE15137CXW:~/homework/linuxibm/my_copy$ cat hello.c #include int main(){ printf("Hello SASTRA"); return 0; } abhinav@abhinav-SVE15137CXW:~/homework/linuxibm/my_copy$ cat hello_org.c #include int main(){ printf("Hello World"); return 0; }

6. Let us create a patch

   A . Create a difference of the two files : The following is the diff output of the 2 file hello_world.c and hello.c

   abhinav@abhinav-SVE15137CXW:~/homework/linuxibm/my_copy$ diff -Naurp hello_org.c hello.c

   — hello_org.c 2014-02-14 13:48:31.039899000 +0530 +++ hello.c 2014-02-14 13:55:51.939895038 +0530 @@ -1,5 +1,5 @@ #include int main(){ - printf("Hello World"); + printf("Hello SASTRA"); return 0; }

   B . Create a patch file by redirecting the output of the to my.patch file . we will send only the patch file ,

   abhinav@abhinav-SVE15137CXW:~/homework/linuxibm/my_copy$ diff -Naurp hello_org.c hello.c > my.patch

   abhinav@abhinav-SVE15137CXW:~/homework/linuxibm/my_copy$ ls hello.c hello_org.c my.patch

   C. patch file looks like this

   abhinav@abhinav-SVE15137CXW:~/homework/linuxibm/my_copy$ cat my.patch — hello_org.c 2014-02-14 13:48:31.039899000 +0530 +++ hello.c 2014-02-14 13:55:51.939895038 +0530 @@ -1,5 +1,5 @@ #include int main(){ - printf("Hello World"); + printf("Hello SASTRA"); return 0; }

7. SEND the patch to upstream ; here we copy it

   abhinav@abhinav-SVE15137CXW:~/homework/linuxibm/my_copy$ cp my.patch ../upstream/

   once this is done we have our my.patch in the out upstream folder abhinav@abhinav-SVE15137CXW:~/homework/linuxibm/upstream$ ls hello.c my.patch

8. Applying the patch we use the ‘patch’ command in the upstream directory : to do this we do the following input redirection : patch -p0 < my.patch

   abhinav@abhinav-SVE15137CXW:~/homework/linuxibm/upstream$ patch -p0 < [my.patch] patching file hello.c

   [,] is not required . That is given for simpler representation .

9. Now let us see the patched hello.c abhinav@abhinav-SVE15137CXW:~/homework/linuxibm/upstream$ cat hello.c

   // #include int main(){ printf("Hello SASTRA"); return 0; }

CONGRATS patch was created and APPLIED

1. CAN I reverse apply the patch ? YES . To reverse the patch we use -R option : abhinav@abhinav-SVE15137CXW:~/homework/linuxibm/upstream$ patch -p0 -R < [my.patch] patching file hello.c Lets us see the File now :) . Guess what ? File is reverse patched . YES!

   abhinav@abhinav-SVE15137CXW:~/homework/linuxibm/upstream$ cat hello.c

   #include int main(){ printf("Hello World"); return 0; }

Thus a patch is Learnt :)