A patch file (or diff file) contains instructions on modifying a set of existing text files from known originals. It's used in Sourceforge projects to publish the newest code changes that didn't yet make it into "official" SVN, so if you want to beta-test and review the lattest proposal for VS code, you need to download and apply patches. It's a very good idea to look into the patch file before applying it (they are plain text, after all). For one, it's a non-reviewed piece of code that will be executable, and you probably would like to make sure it's no more hacky than it's supposed to be. Even if you trust the source, at very least look whether it's really a patchfile and whether you're about to apply it in the same place where it expects the files to be.
Apply patch file
Subversion 1.7 can apply patch on its own] with a single command, e.g.:
Earlier versions of Subversion don't have patch subcommand, so you need other tools.
~/repositories/VegaStrike/trunk/vegastrike$ svn patch ~/tmp/MyLatestVSPatch.patch
In Linux, you probably already have (if you got Subversion package installed on Debian/*Ubuntu, it should be there too)
patch utility, so all you need is to go at the proper base path (relatively to which path of each file is given, the same where diff was taken - usually trunk/vegastrike) - and type in command shell:
/your/working/copy/directory.../trunk/vegastrike$ patch -p0 -i /wherever/you/saved/that/patch.../PatchFileName.patch
If everything worked, you'll get a report like
~/repositories/VegaStrike/trunk/vegastrike$ patch -p0 -i ~/tmp/MyLatestVSPatch.patch
note that pathes here are relative to trunk/vegastrike.
patching file src/cmd/unit_generic.h
patching file src/cmd/unit.cpp
patching file src/cmd/unit_generic.cpp
If you use a Subversion front-end, it may be able to apply patch on its own, or at least open a terminal window where you want it, saving cd around manually (e.g. PySVN Workbench starts command shell at the path selected on the left panel tree).
There probably aren't any pre-installed utilities, but third-party ones are available (e.g. GnuWin32 includes it). Also, in Windows you probably would use Subversion via front-end / GUI client, and advanced ones (e.g. TortoiseSVN) allow to apply patches on their own.
Create patch file
To create patchfiles, you need only Subversion client itself. The proper command looks like this:
- When SVN command is used without extra options like above, it compares the working copy with its backup base. Note that diff (standalone or SVN) will see path relatively to the place where it's running, so it's better to launch it from trunk/vegastrike too, but narrow the scope as needed via parameters - in the example src/cmd/unit.cpp and all files in src/cmd/* are checked for differences, but nothing else.
~/repositories/VegaStrike/trunk/vegastrike$ svn diff src/cmd/ai src/cmd/unit.cpp >~/tmp/MyLatestVSPatch.patch
Creation of diff to SVN base or HEAD is supported by most GUI front-ends, even simple ones.
It's easy to revert a SVN working copy or its part to the original state as it was taken from the repository. But it's also possible to un-apply patches one by one - at least, if the affected files weren't changed after the patch in question was applied (i.e. if more than one of them modified the same file, revert them from the last to the first):
~/repositories/VegaStrike/trunk/vegastrike$ patch -p0 -R -i ~/tmp/MyLatestVSPatch.patch
~/repositories/VegaStrike/trunk/vegastrike$ svn patch --reverse-diff ~/tmp/MyLatestVSPatch.patch