Linux conditional judgment-if statement-case statement-for statement

01. Judging by File type =

　　　　

Common-D,-E,-F

Two types of formats:

TEST-E/root/install.log = Common

[-e/root/install.log] = both spaces must have

Example: [-d/root] && echo "Yes" | | echo "No": Determine if the file exists and whether it is a directory file, yes, not No.

02, according to the file permissions to judge

　　　

Comparison between 03, two files

Comparison between 04 and two numbers + =

　　　　

05. Single Branch If condition statement

If [conditional judgment];then = = Condition judgment Both spaces cannot be omitted

Program

Fi

Or

If [conditional judgment]

Then

Program

Fi

Example: Judging partition usage

#!/bin/bash

#统计根分区使用率

# Author:shencao (E-mail:[email protected])

rect=$ (df-h | grep/dev/sda5 | awk ' {print $} ' | cut-d "%"-f1)
If [$rect-ge 10]
Then
echo "warning! /dev/sda5 is full!! "
Fi

06. Multi-Branch If statement

If [conditional judgment];then = = Condition judgment Both spaces cannot be omitted

Program

Fi

Or

If [conditional judgment]

Then

Procedure for establishing conditions

Else

Conditions do not form a program

Fi

Example: Backing up a MySQL database

#!/bin/bash

#备份 MySQL Database

# Author:shencao (E-mail:[email protected])

date=$ (Date +%y%m%d)
size=$ (DU-SH/ETC)

if [-d/tmp/dbback]
Then
echo "Date is: $date" >/tmp/dbback/db.txt
echo "Size is: $size" >>/tmp/dbback/db.txt
Cd/tmp/dbback
TAR-ZCF etc_$date.tar.gz/etc db.txt $>/dev/null
Rm-rf/tmp/dbback/db.txt
Else
Mkdir/tmp/dbback
echo "Date is: $date" >/tmp/dbback/db.txt
echo "Size is: $size" >>/tmp/dbback/db.txt
Cd/tmp/dbback
TAR-ZCF etc_$date.tar.gz/etc db.txt $>/dev/null
Rm-rf/tmp/dbback/db.txt
Fi

Example 2: Determine if Apache is booting

#!/bin/bash

port=$ (nmap-st 192.168.3.207 | grep tcp | grep http | awk ' {print $} ')

#使用nmap命令扫描服务器, and intercepts the status of the Apache server, assigning the variable port

If ["$port" = = "Open"]
Then
echo "$ (date) HTTP is ok" >>/tmp/httpd_acc.log
Else
/ETC/RC.D/INIT.D/HTTPD Restart &>/dev/null
echo "$ (date) HTTP is reboot!!" >>/tmp/httpd_err.log

Fi

07. Multi-Branch if condition statement

If [conditional statement 1]

Then

Executing the program 1

elif [Conditional Statement 2]

Then

Executing the program 2

Else

Executing the program 2

Fi

08. Case Statement

Example:

　　　　　　

　　　　

Linux conditional judgment-if statement-case statement-for statement