Shell_ 04_ Shell script

Shell Script

Script ： A file consisting of multiple commands （ It can be viewed through a text editor ）

1）Shell Belong to Linux Built in scripts （ Common scripts ：JS、JSP、PHP、SQL、Python etc. ）

2） Script cycle ： One Shell The process of file operation completion

3）Shell Scripts are divided into ： Simple writing （ The accumulation of simple commands ）、 Complex writing （ Programming ）

To write Shell Script

To write Shell The script should follow the following rules ：

（1） File name specification

1） File name naming format ： file name .sh

//.sh The suffix is to distinguish ordinary files , And .sh yes Bash Default suffix

（2） Code specification

1）Shell The first line in the script file must be ：#!/bin/bash

// Indicates the Shell Interpreter

2） Script to “exit N” Form ends （N Is the returned value ）, And N The scope is 0~255

// It can be done by ${?} get N Value , Easy to adjust

// if N The value of exceeds 255, Then divide the value by 256 The remainder of is used as the return status code

Common exit status codes

Status code	explain
0	The command ended successfully
1	Invalid parameter
2	Not suitable Shell command
126	Command execution failed （ No authority ）
127	No specified command
128	Invalid exit parameter
128+x	x Signal related errors
130	By Ctrl+C End
255	Exit status code out of normal range

（3） Annotation specifications

1） Notes should include ： Script function 、 Version information and environment required for operation

// It is better to include ： author 、 Contact information 、 History of script and special commands of script

（4） Call specification

1） The calling of the script requires the user to have the execution permission of the file （x）;

2） Script files can be called by ：

Script path 、sh Script name 、source Script name

// The first two methods are both sub Shell Execute script in , and source Then in the parent Shell Execute script in

（5） Special symbols

Special symbols	meaning
#	Annotation symbols
;	Command separator
&	Commands become background tasks

Such as ： Use Shell Script program , Output “Hello world！”

1)a. Create with .sh Suffix script file

1)b. Write relevant programs （ The first line specifies the interpreter ）, And save

1)c. Give script execution permission , Call script

2)a. Create and write hello.sh Script files

2)b. The contents of the script file are as follows ：

// It is strongly recommended to use the second way , It can ensure the maintenance and update of subsequent scripts

// Scripting tools are best used Vim instead of Vi（Vim There is additional syntax detection function ）

trap command ： Set when Shell The response of the script after receiving the signal

Command format 1：trap command The signal

1） After receiving the specified signal , Run the specified command ;

2） Multiple trap On command , Then only run this trap Command related parts , To execute the specified command ;

Such as ： Use Ctrl+C Termination with trap Command the script that captures the signal

1） To write test23.sh Script files

2） call test23.sh Script files

Command format 2：trap Single dash or double dash The signal // Restore the function of the signal generator

1） If the signal is captured before recovery , According to trap The command specified by the command executes

Such as ： adopt trap After the command captures the signal , Restore the function of the signal generator

1） To write test24.sh Script files

2） call test24.sh Script files

call Shell Script

sh command ：shell command interpreter

Command format ：sh Options File path

1） The most commonly used is to make the system with Bash Function execution file

2）sh Is to execute the script file in the subprocess

Options	meaning
-v	perform shell Before script , First output the content to the screen
-n	Only right shell Script syntax checking , Not implemented
-x	Yes shell The script tracks each statement

// The most commonly used -x Option to modify the script file debug

Such as ： Yes hello.sh Document carried out shell Script tracking and debugging

source command ： At present Bash Execute the document in the environment and take effect immediately

Command format ：source File path

1）source The command is also “.” Click command （ They're exactly the same ）

2）source The command is often used to execute the initialization file just modified , Make the document effective immediately

3）source Is to execute the script file in the parent process

Other ways to call Shell Script ：

1） Call with absolute path or relative path ;

2） adopt Shell The absolute path of the interpreter and the path of the script file are called ;

// Such as ：/bin/bash File path