Note. All examples are applied in Drupal context.

Patch naming convention

Adhere to a strict patch naming convention: Given you are using a board ticketing system, I propose this model:

[issue_name][short-description][issue-number]-[comment-number]

e.g: media-indexOf-IE-2108647-4.patch

Why: sometimes patches become obsolete. This facilitate their removal As for now is impossible or hard to guess what each patch is doing. Later you may easily find on a technical board it’s reasoning and description. You can use JIRA ticket number for example.

Other options: -b – keep a file backup Upon startup patch command try to figure out the type of diff listing unless overriden by -c (context), -e, -n, or -u (unified).

The names of the files to be patched are usually taken from the patch file, but if there’s just one file to be patched it can specified on the command line as original file.

How to read a patch

Understanding hunks

If you would open the .patch file, you’d see that it’s organized in a bunch of segments, so-called “hunks”. Every hunk identifies corresponding pieces of code (by line numbers) in the old and new version, the differences between those pieces of code, and similarities between them (the “context”).

A hunk might fail if the similarities of a hunk don’t match what’s in the original file. When you see this error, it is almost always because you’re using a patch for the wrong version of the code you’re patching.

Then follow sets of changes, called hunks. Each hunk starts with a line that contains,

  1. enclosed in @@, showing the context start line,

  2. no-of-lines in the file before (with a -) and after (with a +) the changes. After that come the lines from the file. Lines starting with a - are deleted, lines starting with a + are added. Each line modified by the patch is surrounded withbefore and after.

An addition looks like this:

@@ -75,6 +77,8 @@
 foo
 bar
 baz
+line1
+linemore
 and still context
That means, in the original file after line 78 (= 75 + add . These will be lines 80 (= 77 + through.
A deletion looks like this:
@@ -75,7 +75,6 @@
 foo
 bar
 baz
-linemore
 and still context
That means, delete line 78 (= 75 + in the original file. The unchanged context will be on lines.
Finally, a change looks like this:
@@ -70,7 +70,7 @@
 foo
 bar
 baz
-red
+blue
 more context
 and more
 still context

That means, change line 73 (= 70 + in the file before all changes, which contains red to blue. The changed line is also line 73 (= 70 + in the file after all changes.

Windows vs Unix file format

I suspect that this error is more related with the file format that with the patch offset. We have been able to apply the patch doing the following:

$ vi configure_links-1277444-1.patch

There

:set ff=unix <enter>
:wq! <enter>

Once the file format is changed and we are again in the prompt:

$ patch -p1 < configure_links-1277444-1.patch
patching file content_lock.info
Hunk #1 succeeded at 14 (offset 3 lines).
patching file modules/content_lock_timeout/content_lock_timeout.info
Hunk #1 succeeded at 8 (offset 3 lines).

Then I checked manually and the files were been patched correctly. Did you already tried this? Please let us know if this work also for you.

If you add a new file:

--- /dev/null
+++ sites/all/modules/contributed/eu_cookie_compliance/js/eu_cookie_compliance.admin.js

Applying patches with patch

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

The -p level When file to be patched and patch are in different folders you have to be careful about setting a “p level”. The p level instructs patch to ignore parts of the path name so that it can identify the files correctly.

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.

Example #1

Patch is to be found in sites/all/modules/contributed/date , while file to be patch is sites/all/modules/contributed/date/date_views/includes/date_views_filter_handler_simple.inc

2 level deeper.

In this case you run

/sites/all/modules/contributed/date $ patch -p1 -R < 1876168-47-exposed_date_filter_groups.patch
patching file date_views/includes/date_views_filter_handler_simple.inc

Example #2

If you file to be patch is /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 revert patch,

use the -R flag, ie
patch -p5 -R < baz.patch
or git apply -R path/file.patch

Patches can be undone, or reversed, with the ‘-R’ option:

$ patch -R < /path/to/file 
Apply patch to multiple files:
host # patch -p0 -i patchfile.patch
patching file tmpdir1/file1
patching file tmpdir1/file2
Creating patches with diff

with single files,

To create a patch for a single file, use the form:

diff -u original.c new.c > original.patch

-u option will generate the context or entire source directories.

  1. make a copy of the tree:
cp -R original new

Make any changes required in the directory new/. Then create a patch with the following command:

diff -rupN original/ new/ > original.patch

This generates a unified multifile patch.

That’s all you need to get started with diff and patch. For more information use:

man diff
man patch

Diff and colordiff

Generate a patch using diff command:

diff -c tmpdir1 tmpdir2  > patchfile.patch
cat patchfile.patch

If you prefer to use a terminal, colordiff (in the colordiff package) provides syntax highlighting. If the patch is long, you may want to use less to look at it.

References Bertheau, Markus - How to read a patch or a diff