Linux 逐行比较文件：diff命令

Linux 求出两个文件的差别：diff命令介绍

Linux diff命令用于比较文件的差异。

diff以逐行的方式，比较文本文件的异同处。如果指定要比较目录，则diff会比较目录中相同文件名的文件，但不会比较其中子目录。

diff 命令是一个分析文件信息的命令，可以打印出文件之间的差异。它可以逐行地比较两个文件的内容，也可以递归地比较文件夹的内容。diff 命令的输出内容可以让我们知道要使两个文件相同需要做哪些修改，这对于我们的工作很有帮助。

用法

diff file1 file2
diff –u file1 file2

功能

• 比较两个版本的文本文件，以寻找两者间差别

输出格式

• normal，
• unified (-u)

normal格式

normal格式：列出一个如何将原文件file1转化为新文件file2的指令

• 这些指令有
  • a（Add），
  • c（Change）
  • d（Delete）
• 指令字母左边的行号是file1的行号，右面是file2的行号
• 列出内容时，
  • 大于号后边的内容是需要在file1文件中增加的内容；
  • 小于号后边的内容是需从file1中删除的内容

normal格式文件转化指令

更换指令c

25c25,26
< #define MAX_WEIGHT 2000000000 
---
> /* max signed 32-bit integer */
> #define MAX_WEIGHT 0x7fffffff

将原文件file1的第25行更换(change)成新文件file2的的第25~26行。

删除指令d

61,62d60
<                 x2 = ht[j].weight;
<                 m2 = j;

将原文件file1第6l~62行删除(delete)后，后面的内容与新文件file2的第60行之后一致

增加指令a

68a67,68
>         ht[i].parent = -1;
>         printf("Create new tree\n");

将原文件file1的第68行增加(add)新文件file2中的第67~68行

unified格式

unified在git中使用的就是这种格式。

$ diff -u0 ht.c ht2.c 
--- ht.c 2018-11-14 18:18:59.595497610 +0800
+++ ht2.c       2018-11-17 08:22:58.191858259 +0800
@@ -25 +25,2 @@
-#define MAX_WEIGHT 2000000000 
+/* max signed 32-bit integer */
+#define MAX_WEIGHT 0x7fffffff
@@ -50,2 +51 @@
- x1 = x2 = MAX_WEIGHT;
- m1 = m2 = 0;
+        x1 = MAX_WEIGHT;
@@ -61,2 +60,0 @@
- x2 = ht[j].weight;
- m2 = j;
@@ -68,0 +67,2 @@
+        ht[i].parent = -1;
+        printf("Create new tree\n");

以下的信息表示两个文件差异的内容：

@@ -25 +25,2 @@
-#define MAX_WEIGHT 2000000000 
+/* max signed 32-bit integer */
+#define MAX_WEIGHT 0x7fffffff

表示删除第一个文件ht.c第25行的内容，然后在第25行添加两行新内容。

@@ -50,2 +51 @@
- x1 = x2 = MAX_WEIGHT;
- m1 = m2 = 0;
+        x1 = MAX_WEIGHT;

删除第一个文件的50行之后的两行内容。然后在第51行添加一行内容。

@@ -61,2 +60,0 @@
- x2 = ht[j].weight;
- m2 = j;

删除第一个文件第61行之后的两行内容

@@ -68,0 +67,2 @@
+        ht[i].parent = -1;
+        printf("Create new tree\n");

在第67行后添加两行内容。

diff 标准输出

[root@localhost cmp]# cat -n a.txt 
     1    this is line a
     2    this is line b
     3    helloworld!
     4    this is line d
     5    this is a new line
[root@localhost cmp]# cat -n b.txt 
     1    this is line a
     2    this is line b
     3    this is line c
     4    this is line d
[root@localhost cmp]# diff a.txt b.txt 
3c3
< helloworld!
---
> this is line c
5d4
< this is a new line
[root@localhost cmp]# 

diff命令输出信息

diff 命令所参考的不是第一个文件，而是第二个文件，它的输出信息有以下几种字符：

• a : 表示必须文件1必须 添加一行 才能和文件2相同
• c : 表示必须文件1必须 修改行 才能和文件2相同
• d : 表示必须文件1必须 删除一行 才能和文件2相同
• 字符前的数字表示第一个文件中的行数，
• 字符后的内容表示第二个文件中的行数。
• < 表示引用的第一个文件中的内容，
• > 表示引用的第一个文件中的内容。

所以上面的输出信息的含义如下：

3c3              # 根据第2个文件b.txt的第3行,第一个文件a.txt的第3行需要改变的内容，我猜这里的c应该是change的意思
< helloworld!    # 第1个文件a.txt的第3行的内容
---              # 分隔符
> this is line c # 第2个文件b.txt的第3行的内容
5d4              # 根据第2个文件的第4行，第一个文件a.txt的第5行需要删除掉的内容
< this is a new line

diff a.txt b.txt

[root@localhost cmp]# diff a.txt b.txt 
3c3
< helloworld!
---
> this is line c
5d4
< this is a new line
[root@localhost cmp]# 

为了使得a.txt和b.txt相同，我们必须

• 修改a.txt的第3行的内容。(3c3)
• 删除a.txt的第5行的内容。(5d4)

diff b.txt a.txt

现在调换两个文件的位置,输出如下：

[root@localhost cmp]# diff b.txt a.txt 
3c3
< this is line c
---
> helloworld!
4a5
> this is a new line
[root@localhost cmp]# 

可以看到如果要使得b.txt和a.txt内容一样。

• 修改b.txt的 第3行的内容。
• 在b.txt的第4行之后添加内容。

diff -c：上下文格式

[root@localhost cmp]# diff -c a.txt b.txt 
*** a.txt    2021-05-19 11:45:23.117869628 +0800
--- b.txt    2021-05-15 22:41:56.157986437 +0800
***************
*** 1,5 ****
  this is line a
  this is line b
! helloworld!
  this is line d
- this is a new line
--- 1,4 ----
  this is line a
  this is line b
! this is line c
  this is line d
[root@localhost cmp]# 

diff -c输出信息

其中

*** a.txt    2021-05-19 11:45:23.117869628 +0800

表示文件a.txt的信息用星号表示

--- b.txt    2021-05-15 22:41:56.157986437 +0800

表示b.txt的信息用减号表示

*** 1,5 ****   表示下方是a.txt的第1到第5行的内容

--- 1,4 ----  表示下方是b.txt的第1到第4行的内容。

行前有感叹号 表示 该行 需要修改

! helloworld!

和

! this is line c

表示要使得a.txt与b.txt内容一样，需要修改helloworld为this is line c.

行前有减号 表示改行需要删除

- this is a new line

表示要使得a.txt与b.txt内容一样，该行需要删除掉。

[root@localhost cmp]# diff -c b.txt a.txt 
*** b.txt    2021-05-15 22:41:56.157986437 +0800
--- a.txt    2021-05-19 11:45:23.117869628 +0800
***************
*** 1,4 ****
  this is line a
  this is line b
! this is line c
  this is line d
--- 1,5 ----
  this is line a
  this is line b
! helloworld!
  this is line d
+ this is a new line
[root@localhost cmp]# 

行前有加号表示需要添加改行

+ this is a new line

表示要使得b.txt比a.txt多了

this is a new line

这一行

diff -u：统一格式输出

统一输出格式是上下文格式的改进版本，并产生较小的输出。
使用-u选项告诉diff以统一格式打印输出：

[root@localhost cmp]# diff -u a.txt b.txt 
--- a.txt    2021-05-19 11:45:23.117869628 +0800
+++ b.txt    2021-05-15 22:41:56.157986437 +0800
@@ -1,5 +1,4 @@
 this is line a
 this is line b
-helloworld!
+this is line c
 this is line d
-this is a new line
[root@localhost cmp]# 

表示把b.txt的

helloworld!

这样修改为

this is line c

，然后删除

this is a new line

即可得到a.txt

diff命令手册

man diif

https://manned.org/diff.1

tldr diif

[root@localhost cmp]# tldr diff
  diff

  Compare files and directories.
  More information: https://man7.org/linux/man-pages/man1/diff.1.html.

  - Compare files (lists changes to turn old_file into new_file):
    diff old_file new_file

  - Compare files, ignoring white spaces:
    diff -w old_file new_file

  - Compare files, showing the differences side by side:
    diff -y old_file new_file

  - Compare files, showing the differences in unified format (as used by git diff):
    diff -u old_file new_file

  - Compare directories recursively (shows names for differing files/directories as well as changes made to files):
    diff -r old_directory new_directory

  - Compare directories, only showing the names of files that differ:
    diff -rq old_directory new_directory

[root@localhost cmp]# 

cheat diff

[root@localhost ~]# cheat diff
# To view the differences between two files:
diff -u version1 version2

# To view the differences between two directories:
diff -ur folder1/ folder2/

# To ignore the white spaces:
diff -ub version1 version2

# To ignore the blank lines:
diff -uB version1 version2

# To ignore the differences between uppercase and lowercase:
diff -ui version1 version2

# To report whether the files differ:
diff -q version1 version2

# To report whether the files are identical:
diff -s version1 version2

# To diff the output of two commands or scripts:
diff <(command1) <(command2)

# Generate a patch file from two files
diff -Naur version1 version2 > version.patch
[root@localhost ~]# 

参考资料

http://www.weixueyuan.net/a/550.html
https://segmentfault.com/a/1190000023138544
https://www.myfreax.com/diff-command-in-linux/
https://segmentfault.com/a/1190000039105296
https://www.jianshu.com/p/6ee74c2790b1
https://codingdict.com/article/10090
http://blog.itpub.net/29270124/viewspace-2220511/
https://os.51cto.com/art/201311/418930.htm