Shell instruction learning 1

1、 shell The role of

• Automatic batch system initialization program （update, Software installation , Time zone settings , The security policy …）;
• Automated bulk software deployment program ;（LAMP/LNMP/Tomcat/LVS/Nginx）;
• Manage applications （KVM、 Cluster management expansion 、MySQL）;
• Log analysis handler （PV、UV、200、!200、grep/awk）;
• Automated backup recovery procedures （MySQL Full backup / The incremental +Crond）…

2、echo $? Output return value , If correct, it is 0, Not 0 Represents a mistake .
3、 command 1 && command 2 && Have logical judgment , When ordered 1 If the execution is successful, execute the command 2.
4、 command 1 || command 2 When ordered 1 Execution failure , Order 2 perform .
5、&> Redirect mixed output , Including standard output and error output .

#  Output useless information to /dev/null
&> /dev/null

6、sh Script ,bash xxx.sh perform sh xxx.sh It can also be executed .
7、 If you execute through a path , Need to add permission chmod +x xxx.sh.
8、shell The beginning of the script usually says ：#!/usr/bin/bash Its effect is ： Define which interpreter the program uses to execute .
9、 Merge two files cat xx1 >> xx2,> Redirect normal information , Redirection is to overwrite the original file ,>> It is to add .
10、& Indicates that the task is executed in the background .