Chapter 6

Although uncommon, you should also be on the lookout for the opposite of 

feeping creaturism stagnation. Every module must change with time to remain 

vital. Don't let a fear of wild growth prevent perfectly reasonable additions. After 

all, seeing your module grow in ways you never anticipated is part of the fun of 

open source development!

Working with Patches

Accepting code contributions from other developers means working with patches.

A patch is a text file that encodes the differences between two versions of the same 

file. Patch files are meant to be used with the patch program, written by Larry Wall 

(yes, that Larry Wall). Patch files are generated by the diff program.

5

diff looks at 

two versions of a file and outputs the differences. For this reason, patches are often 

called diffs, causing much confusion for the uninitiated.

A typical use of diff and patch is as a way to transmit a change to the source 

from a developer to a maintainer. The developer uses diff to produce a patch file 

that describes the changes made to the files. The patch file is then submitted to the 

maintainer of the project, often by e mailing it to a mailing list or directly to the 

maintainer. If the maintainer accepts the change, then he or she uses the patch

program to apply the changes described in the patch file. The end result is that the 

change made by a developer is transmitted to the project maintainer without 

requiring the entire set of changed files to be exchanged.

TIP The patch program is able to skip any leading junk in a file con 

taining a valid patch. This means that developers can append patches 

to e mails, and you can send the entire e mail to patch without needing 

to manually extract the patch file! This is also why maintainers often 

prefer patches to be appended to e mail rather than attached.

Creating a Single File Patch

The simplest type of patch describes changes to a single file. As an example, I'll 

make a small change to the Data::Counter module introduced in previous 

5. Most Unix systems come with diff and patch installed. If your system is missing these 

utilities, you can find the GNU versions at http://www.gnu.org. Windows users can get diff

and patch by installing the CygWin toolkit available at http://cygwin.com. Note that patch is 

an optional package, and you'll have to select it manually from setup.exe

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