Common learning linux command summary 3- control statements

1, for loop

The for loop format:

for the variable in the list 
do 
    Command1 
    Command2 
    ... 
    Commandn 
DONE 

Note: 

1, such as an alternative command list can ls` ` 

2, braces {1..6}, two intermediate or middle # 123 is a space, not a comma like 

3, for ((i = 11 ; i <= 15; i ++)) # double quotes, no spaces, no description int

2, while circulation

Command the while 
do 
   the Statement (S) BE to IS Command Executed to true IF 
DONE 

Note:

 1, I = $ ((I + 1)) # expressions, double brackets for $ 

2, let I ++ # 1 may increase since let

3, if elif else fi statement

Shell has three if ... else statement:

if ... fi statement;
if ... else ... fi statement;
if ... elif ... else ... fi statement.

if ... elif ... fi statement can be determined for a plurality of conditions, the syntax is:

if [ expression 1 ]
then
   Statement(s) to be executed if expression 1 is true
elif [ expression 2 ]
then
   Statement(s) to be executed if expression 2 is true
elif [ expression 3 ]
then
   Statement(s) to be executed if expression 3 is true
else
   Statement(s) to be executed if no expression is true
fi

　　note:

　　1, read -p "Enter your user name:" userName # save to input variables userName

4, case statements

case statement format is as follows:

case 值 in
模式1)
    command1
    command2
    command3
    ;;
模式2）
    command1
    command2
    command3
    ;;
*)
    command1
    command2
    command3
    ;;
esac

注意：
1、模式1)  半边括号

2、;;模式判断介绍符

3、*)表示其他模式

4、case语句结束标记为反写esac

5、for while语句实例与运行结果

#!/bin/bash
echo  "for ========"

for i in 1 2 3 #中间是空格，不是逗号之类的
do
    echo "i:$i"
done

for i in {5..10} #花括号，中间两点
do
    echo "i:$i"
done

for((i=11;i<=15;i++)) #双括号，没空格，没int说明
do
    echo "i:$i"
done
 
echo “while ======”
i=1
total=0
while((i<=100))
do
    total=$((total+i))
    i=$((i+1)) #表达式，得双括号加$
done
echo "total:$total"

i=1
total=0
while((i<=100))
do
        total=$((total+i))
        let i++  #自加1可以用let
done
echo "total:$total"

[app@VM_4_53_centos cfltest]$ ./forwhile.sh 
for ========
i:1
i:2
i:3
i:5
i:6
i:7
i:8
i:9
i:10
i:11
i:12
i:13
i:14
i:15
“while ======”
total:5050
total:5050

6、if elif else fi语句实例与运行结果

#!/bin/bash
echo "if语句======="
read -p "请输入用户名：" userName  #保存输入的变量到userName

if [ $userName = root ]
then echo "welcome root..."
elif [ $userName = app ]  #elif的写法注意啦
    then echo "welcome app ..."
else
    echo "please go out..."
fi

[app@VM_4_53_centos cfltest]$ ./contorlshell.sh
if语句=======
请输入用户名：root
welcome root...
[app@VM_4_53_centos cfltest]$ ./contorlshell.sh
if语句=======
请输入用户名：app
welcome app ...
[app@VM_4_53_centos cfltest]$ ./contorlshell.sh
if语句=======
请输入用户名：you
please go out...

7、case语句实例与运行结果

#!/bin/bash
echo "case语句=========="

case $1 in   #case in
 start) #半边括号
    echo "starting ..."
 ;;
 stop)
    echo "stopping ..."
 ;;
 restart)
    echo "restart ..." 
 ;;
 *)   #其他情况用 * 表示
    echo "argument error ..."
 ;;  #每个分支结束加两次分号
esac   #case 反过来写

[app@VM_4_53_centos cfltest]$ ./caseesac.sh
case语句==========
argument error ...
[app@VM_4_53_centos cfltest]$ ./caseesac.sh start
case语句==========
starting ...
[app@VM_4_53_centos cfltest]$ ./caseesac.sh restart
case语句==========
restart ...
[app@VM_4_53_centos cfltest]$ ./caseesac.sh stop
case语句==========
stopping ...