How to use diff and patch to update the source code

About updating the source code diff And patch command

• Reference material ：

  ①《 Master Linux》p17,p279–p280

  ②《 happy Linux Command line 》http://billie66.github.io/TLCL/ p291–p295

  ③《 Bird brother Linux Private dishes , Basics 3 edition 》p366–p368

diff command

• It is mainly used to compare the differences between files or directories , coordination patch Command can realize the change between different program source code versions . A common use case is diff The program creates a diff file or patch Patch file , then patch Use this file to update the source code

• diff Comparison commands have different output styles , Here is a record of the most commonly used unified pattern style , I.e. use -u Options

  • Suppose there are two different files file1.txt and file2.txt, As shown below ：

  

• call diff Command to compare , The output style is unified

  diff -u file1.txt file2.txt
  # The output is as follows ：
  

  

  1. The first two lines are the beginning of the file name and timestamp , The first file uses --- Make a mark , For the second file +++ Make a mark
  2. In the third line @@ -1,4 +1,4 @@ It describes that the range of differences in the first file is 1 Go to the first place 4 That's ok , The range of differences in the second document is 1 Go to the first place 4 That's ok ,- It means the first file ,+ Represents the second file
  3. The string after the third line is the text line itself , Start with three characters , Represents different meanings
     • Space Indicates that both files contain line changes ;- Indicates that when updating from one file to the second file, you need to delete and change lines ;+ Indicates that the line change needs to be added when updating from the first file to the second file
  4. Be careful ： The patch file has included all updates / Modify strategy , So when updating, you can update as long as you can find the file

• in addition ：diff It can work in any text file , Source code 、 Configuration files, etc

• Use diff Command to generate difference file or patch file

  diff -Naur old_file new_file > diff_file
  # among old_file and new_file It can be either a file or a directory 
  -N  Indicates if it is a comparison directory , If document A Only appear in a directory , The preset is displayed as Only in.....
  -u  Indicates using unified mode output , That is, the mode described above 
  -r  Indicates recursive comparison of subdirectories 
  -a  Means to compare text files line by line 
  

  for example ：

  diff -Naur file1.txt file2.txt > file.patch
  

• Then we can use patch Command and file.patch Update the patch file

• patch command

  # to update 
  patch -pN < patch_file
  # Restore 
  patch -R -pN < patch_file
  
  -p  Said to ignore N Layer Directory ( This place is a little difficult to understand , I'll say later )
  -R  Means to restore the new file to the old version 
  

  Then, above ： to update file1.txt To file2.txt

  # Type first to include file1.txt and file2.txt Under the directory of , Then execute the order 
  patch < file.patch 
  # We don't need to specify to update / Patched target file , because diff file /file.patch The file name has been included in the title line of the file 
  

  Or update with the following command ：

  -p Parameters are mainly used in directory related places , Suppose there is a patch file with the beginning shown below ：

  

  situation 1： If you are currently in src Under the table of contents , You can directly execute the following commands to update ：

  patch -p0 < file.patch
   or 
  patch < file.patch
  

  situation 2： If the beginning of the patch is different from the current environment , You can use -p Appropriately ignore several levels of directories

  

  That is, if your current directory is package-3.45, There is src Catalog , For the patch file above , You need to ignore the first level directory

  patch -p1 < file.patch
  # among file.patch  You can also use the absolute path to locate the file 
  

  If it is after the source code is updated , You can recompile and build 、 Installed

  make clean main # Clean up the target file first , And then build 
  make install 	# install