Creating a Patch

A patch is really just a textfile which contains a collection of lines to be added or substracted to/from other textfiles.

Create Patch From a git Cherry Pick

git is a source code management tool, which is becoming more and more popular. Creating a patch from a git repo is quite easy, if you know which commit(s) you are looking for.

If you know which commit includes the changes you are interested of, for instance 886600b5a2baa0c88f4d709dbc6ab0896e6565cb, in the root of the git source, do:

The result could look something like this:

   1 commit 886600b5a2baa0c88f4d709dbc6ab0896e6565cb
   2 Author: Kaj Ailomaa <zequence@mousike.me>
   3 Date:   Mon Mar 18 22:15:05 2013 +0100
   4 
   5     added a few lines to a README
   6 
   7 diff --git a/README b/README
   8 index e69de29..4a2b88c 100644
   9 --- a/README
  10 +++ b/README
  11 @@ -0,0 +1 @@
  12 +Adding a few lines to this README
  13 

It contains most of the info we need for patching a Debian source package. It has the actual diff that will change the source code. It also includes the author of the commit, as well as a description of the commit. All this can be used when documenting the patch.

If we were to create a patch from this, all we need to do is:

git show 886600b5a2baa0c88f4d709dbc6ab0896e6565cb > ../my-fix.patch

When applying the patch, only the info following the diff data will be used during patching. The header will be ignored, so don't worry about that.

If making multiple patches, make sure to keep track of which order they are to be applied, as one might overwrite another.

Applying a patch

Applying a patch is generally done by entering the root of the source directory. Then, using the command:

patch -p 1 < /path/to/patch

See the man page for patch to learn more.