Linux (vii) __shell script programming

First, what is a shell script

The shell is a programming language in addition to the command interpreter, and a program written in Shell resembles a DOS batch program.

It is an interface between the user and the operating system.

The Shell scripting language is very good at handling text-type data, because the configuration files in Linux are text files, so the Shell scripting language

Has played a huge role in managing Linux systems.

Second, why learn shell script

• Automated management
• Monitoring management
• Log data processing
• Automatic data backup

Three, basic grammar

The generic file begins with #!/bin/bash, which indicates that the file uses bash syntax and is not set, but this is a specification.

The shell script is in the behavior unit. Note # variables support string variables and integer variables

VI Edit shell script file

Call Mode:

SH script-file

You can add the-X option to view the execution of this script, which facilitates debugging.

./Script-file

Execute shell scripts in./mode you must set file permissions chmod +x filename into an executable file

The. bin file will be used./Call

Shell variables

Name=string

The name variable string is assigned a value with no spaces on either side and is treated as a command

Cases:

V=centos

echo= $v ($ flag a variable)

Date command:

Date

Date +%h:%m:%s

Shell expression:

Simple arithmetic:

b=$ ((5*5+5-3/2))
Echo $b
29
In the Linux shell, we can use $ (()) to put the expression in parentheses to achieve the function of the operation.

Or you can use $[].

Processing of strings

and user interaction:

Read command

P is the abbreviation for prompt, which is the cue message given by this switch item, such as
Read-p ' please input choice:\n ' Choice
The screen will display when you enter:
Please input choice:
Then the stuff you type will be saved in the choice variable.

Judge:

Test judgment

Cases:

Filename=/home/hello.java

Test-f $filename && echo ' Exit ' | | echo ' Not exit '

[] Judging

In particular, note the first, there must be a space between the variable constant and the symbol.

Judge

Cases:

If [-F $filename];then

Echo ' The file is exist '

Fi

Linux (vii) __shell script programming