If Judgment statement for Shell script

If statement

1, according to the file type to judge
-d file) to determine if the file exists and is a character device file (the character device is true)
-e file) to determine if the file exists (exists as true)
[-e/root]
echo $? The output is 0 #判断为真, which is 0
The commonly used formats are:
[-e/root] && echo yes | | Echo No

One, the single branch if conditional statement format has the following two kinds:

If [Conditional judgment type];then
Program
Fi
Or
If [conditional judgment]
Then
Program
Fi

But branching conditional statements need to be aware of several points
The if statement uses the FI end, which differs from the general language using curly braces
· [Conditional judgment] is determined using the test command, so there must be a space between the brackets and the conditional judgment
then after the following and meet the conditions after the execution of the program, can be placed after [], with ";" Segmentation. You can also write a newline, and you don't need to be ";" The

Example: Judging partition usage
#!/bin/bash
#统计根分区使用率
#Author: Xuyizhong (e-mail:[email protected])
rate=$ (df-h |grep "/dev/vda1" | awk ' {print $} ' | cut-d "%"-f1)
#把根分区使用率作为变量值赋予变量rate
If [$rate-ge 80]
Then
echo "warning! /DEV/VDA1 is FULL!!! "
Fi

Two, two-branch if condition statement

If [conditional judgment]
Then
When conditions are established, the procedure to be executed
Else
Another program that executes when the condition is not established
Fi
Example 1: Backing up the MySQL database
#!/bin/bash
#备份mysql数据库
#Author: Xuyizhong (e-mail:[email protected])
Ntpdate asia.pool.ntp.org &>/dev/null
#同步系统时间
date=$ (Date +%y%m%d)
#把当前系统时间按照 "Month and Day" format assigns variable date
size=$ (Du-sh/var/lib/mysql)
#统计mysql数据库的大小, and give the size variable
if [-d/tmp/dbbak]
#判断 the/tmp/dbbak folder exists, there is execution then, there is no execute else
Then
echo "Date: $date" >/tmp/dbbak/dbinfo.txt
echo "Data size: $size" >>/tmp/dbbak/dbinfo.txt
Cd/tmp/dbbak
TAR-ZCF mysql-lib-$date. Tar.gz/var/lib/mysql dbinfo.txt &>/dev/null
Rm-rf/tmp/dbbak/dbinfo.txt
Else
Mkdir/tmp/dbbak
echo "Date: $date" >/tmp/dbbak/dbinfo.txt
echo "Data size: $size" >>/tmp/dbbak/dbinfo.txt
Cd/tmp/dbbak
TAR-ZCF mysql-lib-$date. Tar.gz/var/lib/mysql dbinfo.txt &>/dev/null
Rm-rf/tmp/dbbak/dbinfo.txt
Fi

Example 2: Determine if Apache is booting
#!/bin/bash
#Author: Xuyizhong (e-mail:[email protected])

port=$ (nmap-st 192.168.1.156 | grep tcp |grep HTTP |awk ' print $ ')
#使用nmap命令扫描服务器, and intercepts the status of the Apache service, assigning the variable port
If ["$port" = = "Open"]
Then
echo "$ (date) httpd is ok!" >>/tmp/autostart-acc.log
Else
/ETC/RC.D/INIT.D/HTTPD Start &>/dev/null
echo "$ (date) Restart httpd!" >>/tmp/autostart-err.log
Fi

#自己将apache停止 to see if Apache will automatically restart!

Three, multi-branch if condition branch

If [conditional judgment 1]
Then
When the conditional judgment 1 is established, the execution of the program 1
elif [conditional judgment 2]
Then
When the conditional Judgment 2 is established, the execution of the program 2
... Omit more conditions ...
Else
When all conditions are not true, the final execution of this program
Fi

Example 1: Judging what the user has entered the command
#!/bin/bash
#Author: Xuyizhong (e-mail:[email protected])

Read-p "Please input a filename:" File
#接收键盘的输入, and assign the variable file

If [-Z "$file"]
#判断file变量是否为空
Then
echo "Error,please input a filename"
Exit 1
elif [!-e "$file"]
#判断file的值是否存在
Then
echo "Your input is not a file!"
Exit 2
Elif [-F "$file"]
#判断file的值是否为普通文件
Then
echo "$file is a regulare file!"
elif [-D "$file"]
#判断file的值是否为目录文件
Then
echo "$file is a directory!"
Else
echo "$file is a other file!"
Fi

Case statement

The case statement is the same as the If...elif...else statement, but unlike the if multi-branch statement, the case statement can only judge a conditional relationship, and the IF statement may judge multiple conditional relationships

Case $ variable name in
"Value 1")
If the value of the variable equals the value 1, execute the program 1
;;
"Value 2")
If the value of the variable equals the value 2, execute the program 2
;;
）
If the value of the variable is the value above, execute the program
;;
Esac
Example 1:
#!/bin/bash
#判断用户输入
#Author: Xuyizhong (e-mail:[email protected])
Read-p "Please choose Yes/no" T-cho
#将用户的值赋予给cho
Case $cho in
"Yes")
echo "Your Choose is yes!"
;;
"No")
echo "Your Choose is no!"
;;
)
echo "Your Choose is error!"
;;
Esac
Example 2:
#!/bin/bash
Echo ' Want to shanghai,please input ' 1 '
Echo ' Want to guangzhou,please input ' 2 '
Echo ' Want to chengdu,please input ' 3 '
Read-t 30-p "Please input your choose"-T-cho

Case ' $cho ' in
"1")
echo "Shanghai's ticket is on sale."
;;
"2")
echo "Guangzhou's ticket is on sale."
;;
"1")
echo "Chengdu's ticket is on sale."
;;
*)
echo "Error 1/2/3"
;;
Esac

For loop while loop

If Judgment statement for Shell script