Using patch and diff

Creating a patch using diff

diff is a linux command line program, and is where patch files originated. It requires that you have two copies of the code, one with your changes, and one without. Suppose these two copies are in folders called 'standard_moodle' and 'my_moodle' which are subdirectories of the current folder. Then to create the patch, type:

diff -rup original/ new/ > new2original.patch

Options are:

• u: unified format for patching
• r: recursive
• a: compare line by line, even if not text
• p: add function name to diff file
• N: if file only in 1 directory, treat as empty in the other (overrides -P) IT WILL REMOVE ANY FILE NOT PRESENT IN NEW!!!
• P: may be safer

Applying a patch to sources

See  http://jungels.net/articles/diff-patch-ten-minutes.html

To apply a patch to a single file, change to the directory where the file is located and call patch:

patch < foo.patch

These instructions assume the patch is distributed in unified format, which identifies the file the patch should be applied to. If not, you can specify the file on the command line:

patch foo.txt < bar.patch

Applying patches to entire directories (perhaps the more common case) is similar, but you have to be careful about setting a "p level". What this means is that, within patch files, the files to be patched are identified by path names which may be different now that the files are located on your computer rather than on the computer where the patch was created. The p level instructs patch to ignore parts of the path name so that it can identify the files correctly. Most often a p level of one will work, so you use:

patch -p1 < baz.patch

You should change to the top level source directory before running this command. If a patch level of one does not correctly identify any files to patch, inspect the patch file for file names. If you see a name like

/users/stephen/package/src/net/http.c

and you are working in a directory that contains net/http.c, use

patch -p5 < baz.patch

In general, count up one for each path separator (slash character) that you remove from the beginning of the path, until what's left is a path that exists in your working directory. The count you reach is the p level.

To remove a patch, use the -R flag, ie

patch -p5 -R < baz.patch