用diff和patch生成patch并应用

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本文介绍了如何利用diff生成patch文件，以及如何将这个patch应用到原文件上，实现快速更新。

当我们想在原文件和新文件之间生成patch，并用这个patch文件，应用在原文件上快速完成更新时，可以使用以下步骤：

用diff生成patch

$ echo "12345\ntesting"> old_file 
$ echo "125testing\ntesting1234"> new_file
$ # We have 2 common ways to get the patch
$ # The first way is :
$ diff old_file new_file > file_patch
$ # We can see the patch are generated by lines
$ cat file_patch
1c1
< 12345\ntesting
---
> 125testing\ntesting1234
$ # The second way is :
$ diff -c old_file new_file > c_file_patch
$ # Then we can see the patch are generated by contents
$ cat c_file_patch
*** old_file    2018-12-27 21:06:57.922518425 +0800
--- new_file    2018-12-27 21:07:11.551401751 +0800
***************
*** 1 ***
! 12345\ntesting
--- 1 ----
! 125testing\ntesting1234
$ # We also can get one whole patch for files of the whole directories
$ mkdir -p new_dir old_dir
$ echo "123" > new_dir/test_1.txt
$ echo "789testing" > new_dir/test_2.txt
$ echo "356" > old_dir/test_1.txt
$ echo "35678" > old_dir/test_2.txt
$ diff -c -r old_dir/ new_dir > dir_patch
$ # let use the output
$ cat dir_patch
diff -c -r old_dir/test_1.txt new_dir/test_1.txt
*** old_dir/test_1.txt  2018-12-27 21:55:38.654094697 +0800
--- new_dir/test_1.txt  2018-12-27 21:55:18.719294247 +0800
***************
*** 1 ****
! 356
--- 1 ----
! 123
diff -c -r old_dir/test_2.txt new_dir/test_2.txt
*** old_dir/test_2.txt  2018-12-27 21:55:48.594995187 +0800
--- new_dir/test_2.txt  2018-12-27 21:55:29.630185028 +0800
***************
*** 1 ****
! 35678
--- 1 ----
! 789testing
diff -c -r old_dir/test_1.txt new_dir/test_1.txt
*** old_dir/test_1.txt  2018-12-27 21:55:38.654094697 +0800
--- new_dir/test_1.txt  2018-12-27 21:55:18.719294247 +0800
***************
*** 1 ****
! 356
--- 1 ----
! 123
diff -c -r old_dir/test_2.txt new_dir/test_2.txt
*** old_dir/test_2.txt  2018-12-27 21:55:48.594995187 +0800
--- new_dir/test_2.txt  2018-12-27 21:55:29.630185028 +0800
***************
*** 1 ****
! 35678
--- 1 ----
! 789testing

应用patch改变原来的文件

$ # patch single file
$ patch old_file -i c_file_patch 
patching file old_file
$ diff old_file new_file 
$ # No difference
$ # patch multiple files for directories
$ patch -i dir_patch -p0
patching file old_dir/test_1.txt
patching file old_dir/test_2.txt
$ diff -c -r old_dir/ new_dir/
$ # No difference
$ # Let us see how the '-p' means here
$ # Let us prepare one directoy
$ tree old_dir/
old_dir/
|-- sub_1
|   |-- sub_2
|   |   `-- sub_4
|   |       `-- test_4.txt
|   |-- sub_3
|   |   `-- test_3.txt
|   `-- test_2.txt
`-- test_1.txt

4 directories, 4 files
$ tree new_dir/
new_dir/
|-- sub_1
|   |-- sub_2
|   |   |-- sub_4
|   |   |   `-- test_4.txt
|   |   `-- test_5.txt
|   |-- sub_3
|   |   `-- test_3.txt
|   `-- test_2.txt
`-- test_1.txt

4 directories, 5 files
$ # get the patch
$ diff -c -r old_dir/ new_dir/
diff -c -r old_dir/sub_1/sub_2/sub_4/test_4.txt new_dir/sub_1/sub_2/sub_4/test_4.txt
*** old_dir/sub_1/sub_2/sub_4/test_4.txt        2018-12-27 22:19:20.479215655 +0800
--- new_dir/sub_1/sub_2/sub_4/test_4.txt        2018-12-27 22:21:53.496338977 +0800
***************
*** 1 ****
! 123457878786dddddd
--- 1 ----
! 12d3457878786dddddd
Only in new_dir/sub_1/sub_2: test_5.txt
diff -c -r old_dir/sub_1/test_2.txt new_dir/sub_1/test_2.txt
*** old_dir/sub_1/test_2.txt    2018-12-27 22:18:15.191596826 +0800
--- new_dir/sub_1/test_2.txt    2018-12-27 22:21:26.359494452 +0800
***************
*** 1 ****
--- 1,2 ----
  123456
+ helloworld
diff -c -r old_dir/test_1.txt new_dir/test_1.txt
*** old_dir/test_1.txt  2018-12-27 22:17:45.537770449 +0800
--- new_dir/test_1.txt  2018-12-27 22:21:14.283563638 +0800
***************
*** 1 ****
! 123
--- 1 ----
! 123dddd
$ # Let us see without the '-p' parameter
$ patch -i dir_patch 
can not find file to patch at input line 4
Perhaps you should have used the -p or --strip option?
The text leading up to this was:
--------------------------
|diff -c -r old_dir/sub_1/sub_2/sub_4/test_4.txt new_dir/sub_1/sub_2/sub_4/test_4.txt
|*** old_dir/sub_1/sub_2/sub_4/test_4.txt       2018-12-27 22:19:20.479215655 +0800
|--- new_dir/sub_1/sub_2/sub_4/test_4.txt       2018-12-27 22:21:53.496338977 +0800
--------------------------
File to patch: 
$ # It shows us to use the '-p' parameter
$ patch -i dir_patch -p0
patching file old_dir/sub_1/sub_2/sub_4/test_4.txt
patching file old_dir/sub_1/test_2.txt
patching file old_dir/test_1.txt
$ # Let us confirm the result
$ diff -c -r old_dir/ new_dir/
Only in new_dir/sub_1/sub_2: test_5.txt
$ # We can see the existing files are patched. Patch does not create new files
$ # Why we use 'p0' here?
$ # Because we create patches and apply patches under the same path
$ # If we do not do all thing under the same path, we need to specify the '-p' parameters. Let us see the following example 
$ diff -r -c hello/old_dir/sub_1/test_2.txt hello/new_dir/sub_1/test_2.txt
*** hello/old_dir/sub_1/test_2.txt      2018-12-27 22:33:01.610511164 +0800
--- hello/new_dir/sub_1/test_2.txt      2018-12-27 22:21:26.359494452 +0800
***************
*** 1 ****
--- 1,2 ----
  123456
+ helloworld
$ diff -r -c hello/old_dir/sub_1/test_2.txt hello/new_dir/sub_1/test_2.txt > p_dir_patch
$ cp p_dir_patch hello
$ cd hello
$ patch -i p_dir_patch -p1
patching file old_dir/sub_1/sub_2/sub_4/test_4.txt
patching file old_dir/sub_1/test_2.txt
$ # Here we use the 'p1', because we need to omit the first slash 'hello'. We have been on the 'hello' directory