In-depth understanding of patch files: diff instruction generation and common parameter analysis

patch files are generated by diff instructions (linuxdiff, svndiff, gitdiff, gitformat-patch).

First, let’s introduce the diff command and its common parameters:

diff:

The function of diff is to compare the differences between two files and then record them, which is the so-called diff patch. Sentence format: diff [option] source file (folder) destination file (folder) Linux operating system is good, it is to patch the source file (folder) linux patchMarco linux to make it into the destination file (clip), the term is "upgrade". The three most commonly used options are introduced below:

-r is a recursive option. If you set this option linux to patch, diff will compare all corresponding files in the source code directories of two different versions, including subdirectory files.

-N option ensures that the patch file will correctly handle the situation where the file has been created or deleted.

-u option creates patch files in a unified format that is more compact than the default format.

2、patch

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NAME

patch-applyadifffiletoanoriginal

SYNOPSIS

patch[options][originalfile[patchfile]]

butusuallyjust

patch-pnum

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Simply put, patch is to use the patch made by diff to convert the source file (folder) and the destination file (folder). This means that you can have a source file (folder)->destination file (folder), or a destination file (folder)->source file (folder). Here are some of the most commonly used options:

-p0 option is to find the destination file (folder) from the current directory

-p1 option should ignore the first level directory and start searching from the current directory.

Similar -p2 option should ignore the second level directory;

......

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Here is an example:

---old/modules/pcitableMonSep2711:03:561999

+++new/modules/pcitableTueDec1920:05:412000

If you use the parameter -p0, it means to find a folder called old from the current directory, and look for the pcitable file under modules under it to perform the patch operation.

If you use the parameter -p1, it means ignoring the first-level directory (that is, regardless of old), looking for the modules folder from the current directory, and looking for pcitable under it. The premise for this is that the current directory must be the directory where modules are located. The diff patch file can be in any location, as long as the path to the diff patch file is specified. In fact, you can use relative paths or absolute paths. But I usually use relative paths.

****************************************************** *************

-E option indicates that if an empty file is found, delete it

-R option indicates that the "new" files and "old" files in the patch file are now to be exchanged (actually, it is to patch the new version and make it become the old version)

Structure of patch file

Patch head

The patch header is two lines starting with ---/+++, which represent the files to be patched. The beginning of --- represents the old file, and the beginning of +++ represents the new file.

Multiple patches in one patch file

A patch file may contain many sections starting with ---/+++, and each section is used to apply a patch. So a patch file can contain many patches.

Blocks

Blocks are the places to change in the patch. It usually starts and ends with something that doesn't need to be changed. They are just used to indicate the location to be changed. They usually start with @@ and end with the beginning of another block or a new patch header.

Indentation of blocks

block will be indented by one column, and this column is used to indicate whether the line should be lowered or deleted.

First column of blocks

+ sign indicates that this line needs to be added.

- sign indicates that this line should be deleted.

No minus sign or negative sign means it is just a reference and does not need to be changed.

Usage:

patch-p0

patch-p1

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