Generate and Apply patch in linux using diff and patch commands

Generate patch file:

Patch file says the difference between the existing version and the ‘patched’ version of the file.

Once you have edited the source you can create patch file using diff command…

I normally use below syntax of “diff” for creating a patch file..

#diff -Naur “original file” “modified version”

for ex: suppose u have below file in the system..

[root@humbles-lap patch]# cat main_orig.c

# include <stdio.h>
int main ()

{

    printf (“\n I am original source \n”);

}
[root@humbles-lap patch]# cat main.c

# include <stdio.h>
int main ()

{

    printf (“\n I am patched source \n”);

}
[root@humbles-lap patch]# diff -Naur main_orig.c main.c

— main_orig.c    2012-07-19 01:48:26.195898607 +0530

+++ main.c    2012-07-19 01:48:37.497899155 +0530

@@ -2,5 +2,5 @@
int main ()

{

–    printf (“\n I am original source \n”);

+    printf (“\n I am patched source \n”);

}

[root@humbles-lap patch]#

As this is an example, I used diff against different files “main_orig.c” and “main.c”, don’t get confused with that .. 🙂

“-” and “+” signs tell you which line is removed and which is added in its place..

How to apply a patch in a Linux system.

To apply a patch, you can use the “patch” command.

#patch -p1 <“patch file”

ex:

#patch -p1 < main.patch

“-pnum” option controls how file names found in the patch file are used/treated..

Refer #man patch file for more information on this..