diff
比较相似文件的差异（以行为单位），还可以生成用以更新的“补丁文件”
及指定目录下文件名的不同
diff比较两个目录下文件名的不一致
[root@localhost tmp]# ls aaaa
my.cnf
[root@localhost tmp]# ls bbbb
myy.cnf
[root@localhost tmp]# ls
aaaa bbbb my.cnf myyy.cnf
[root@localhost tmp]# diff aaaa bbbb
Nur in aaaa: my.cnf.
Nur in bbbb: myy.cnf.
运行结果提示出了不同的文件名，安装的vagrant默认不知是哪里的语言，还没修改过来，了解意思就好。。。
[root@localhost tmp]# cat -n my.cnf
1 [mysqld]
2 datadir=/var/lib/mysql
3 socket=/var/lib/mysql/mysql.sock
4 # Disabling symbolic-links is recommended to prevent assorted security risks
5 symbolic-links=0
6 # Settings user and group are ignored when systemd is used.
7 # If you need to run mysqld under a different user or group,
8 # customize your systemd unit file for mariadb according to the
9 # instructions in http://fedoraproject.org/wiki/Systemd
10
11 [mysqld_safe]
12 log-error=/var/log/mariadb/mariadb.log
13 pid-file=/var/run/mariadb/mariadb.pid
14
15 #
16 # include all files from the config directory
17 #
18 !includedir /etc/my.cnf.d
19
[root@localhost tmp]# cp my.cnf mmmm.cnf
[root@localhost tmp]# diff my.cnf mmmm.cnf
相同内容的文件，运行diff比较之后没有输出。
[root@localhost tmp]# cat my.cnf | sed -e ‘4d‘ -e ‘6c this line was replaced!‘ >myyy.cnf
[root@localhost tmp]# cat -n myyy.cnf
1 [mysqld]
2 datadir=/var/lib/mysql
3 socket=/var/lib/mysql/mysql.sock
4 symbolic-links=0
5 this line was replaced!
6 # If you need to run mysqld under a different user or group,
7 # customize your systemd unit file for mariadb according to the
8 # instructions in http://fedoraproject.org/wiki/Systemd
9
10 [mysqld_safe]
11 log-error=/var/log/mariadb/mariadb.log
12 pid-file=/var/run/mariadb/mariadb.pid
13
14 #
15 # include all files from the config directory
16 #
17 !includedir /etc/my.cnf.d
18
制造不同，并另存为新文件myyy.cnf
[root@localhost tmp]# diff my.cnf myyy.cnf
4d3
< # Disabling symbolic-links is recommended to prevent assorted security risks
6c5
< # Settings user and group are ignored when systemd is used.
---
> this line was replaced!
仔细理解下diff的输出：它并不执着于两个文件内容对应的行号是否完全一致。<号后对应的是命令中左侧文件的不一致部分，可以理解为箭头指向左侧，相应>号后是命令中右侧文件的不一致部分。d表示删掉，4d3表示定位到左侧文件第四行内容在右侧文件中被删除，右侧文件定位到第三行后。6c5则表示左侧文件的第六行被右侧文件第五行替换，之后分别列出了相应内容。也可以理解为，左侧文件经过在第几行处的d 、 c操作即可得出右侧新文件
下面再制造一个不同之处多些的文件
[root@localhost tmp]# cat my.cnf | sed -e ‘4d‘ -e ‘6c this line was replaced!‘ -e ‘9i this is insert part‘ > new.cnf
[root@localhost tmp]# sed -i ‘12d‘ new.cnf
[root@localhost tmp]# cat new.cnf | grep symbolic
symbolic-links=0
[root@localhost tmp]# cat new.cnf | grep symbolic > 111
[root@localhost tmp]# cat 111
symbolic-links=0
[root@localhost tmp]# sed -i ‘4d‘ new.cnf ; cat 111 >>new.cnf
[root@localhost tmp]# cat -n my.cnf
1 [mysqld]
2 datadir=/var/lib/mysql
3 socket=/var/lib/mysql/mysql.sock
4 # Disabling symbolic-links is recommended to prevent assorted security risks
5 symbolic-links=0
6 # Settings user and group are ignored when systemd is used.
7 # If you need to run mysqld under a different user or group,
8 # customize your systemd unit file for mariadb according to the
9 # instructions in http://fedoraproject.org/wiki/Systemd
10
11 [mysqld_safe]
12 log-error=/var/log/mariadb/mariadb.log
13 pid-file=/var/run/mariadb/mariadb.pid
14
15 #
16 # include all files from the config directory
17 #
18 !includedir /etc/my.cnf.d
19
[root@localhost tmp]# cat -n new.cnf
1 [mysqld]
2 datadir=/var/lib/mysql
3 socket=/var/lib/mysql/mysql.sock
4 this line was replaced!
5 # If you need to run mysqld under a different user or group,
6 # customize your systemd unit file for mariadb according to the
7 this is insert part
8 # instructions in http://fedoraproject.org/wiki/Systemd
9
10 [mysqld_safe]
11 pid-file=/var/run/mariadb/mariadb.pid
12
13 #
14 # include all files from the config directory
15 #
16 !includedir /etc/my.cnf.d
17
18 symbolic-links=0
[root@localhost tmp]# diff my.cnf new.cnf
4,6c4
< # Disabling symbolic-links is recommended to prevent assorted security risks
< symbolic-links=0
< # Settings user and group are ignored when systemd is used.
---
> this line was replaced!
8a7
> this is insert part
12d10
< log-error=/var/log/mariadb/mariadb.log
19a18
> symbolic-links=0
这样似乎理解得更全面些。结合内容理解一下diff的运行结果。注意4，6是指左侧文件的第四五六行（四到六），而不是第四和六。
[root@localhost tmp]# diff -u my.cnf new.cnf > 222
[root@localhost tmp]# cat 222
--- my.cnf 2017-07-31 05:23:33.351268214 +0200
+++ new.cnf 2017-07-31 07:19:28.378359268 +0200
@@ -1,15 +1,13 @@
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
-# Disabling symbolic-links is recommended to prevent assorted security risks
-symbolic-links=0
-# Settings user and group are ignored when systemd is used.
+this line was replaced!
# If you need to run mysqld under a different user or group,
# customize your systemd unit file for mariadb according to the
+this is insert part
# instructions in http://fedoraproject.org/wiki/Systemd
[mysqld_safe]
-log-error=/var/log/mariadb/mariadb.log
pid-file=/var/run/mariadb/mariadb.pid
#
@@ -17,3 +15,4 @@
#
!includedir /etc/my.cnf.d
+symbolic-links=0
显示出公共行，方便比对。其中-后内容为左侧文件数据，+后为右侧文件数据
patch
根据diff -u file1 file2 命令运行结果更新file1内容与file2一致
[root@localhost tmp]# patch -p0 < 222
patching file my.cnf
[root@localhost tmp]# diff my.cnf new.cnf
[root@localhost tmp]# patch -R -p0 < 222
patching file my.cnf
[root@localhost tmp]# diff my.cnf new.cnf
4,6c4
< # Disabling symbolic-links is recommended to prevent assorted security risks
< symbolic-links=0
< # Settings user and group are ignored when systemd is used.
---
> this line was replaced!
8a7
> this is insert part
12d10
< log-error=/var/log/mariadb/mariadb.log
19a18
> symbolic-links=0
-p0取消目录层级。-R是反向的意思，还原更新。所以新旧文件顺序，在用diff生成patch文件时就很重要，一定习惯 旧文件 新文件 这样的比对顺序。
待续。。。
原文地址：http://lybliangliang.blog.51cto.com/3808302/1952360
