Occasionally I write things here simply so that I won't forget them, here's one of them. Applying patches is something I do infrequently enough that I have to re-figure it out each time.

If you have a patch file called my.patch that looks like this (in part):

=== modified file 'cogapp/cogapp.py'
—- cogapp/cogapp.py 2005-12-04 20:27:41 +0000
+++ cogapp/cogapp.py 2008-05-21 09:00:08 +0000
@@ -37,6 +37,7 @@
                     A %s in the CMD will be filled with the filename.
     -x          Excise all the generated output without running the generator
     -z          The [[[end]]] marker can be omitted, and is assumed at eof.
+    -N          Write the output as binary file (with LF line-endings).
     -v          Print the version of cog and exit.
     -h          Print this help.
 """

then to apply the patch, cd to the directory that has cogapp in it, and use this command:

patch -p0 < my.patch

The patch command is one of those inscrutable Unix-culture tools which does not behave as I expect. In this case, there seems to be no syntax that names my.patch explicitly, only an input redirect works. And zero seems not to be the default for the -p switch, so it needs to be specified, but the help text doesn't mention the default value, so I'm not sure what it is.