Shell编程——第四章 控制流结构

笔记

#流控制是什么

#if语句
#if语句必须以单词fi终止
#if条件、then语句、fi

#编辑iftest
vi iftest
#查看iftest内容
cat iftest
#!/bin/bash
#if test
#this is a comment line, all comment lines start with a #
if [ "10" -lt "12" ]
then
        #yes 10 is less than 12
        echo "Yes, 10 is less than 12"
fi

#改变权限
[root@localhost 0402]# chmod 755 iftest
#执行
[root@localhost 0402]# ./iftest
Yes, 10 is less than 12

#查看test命令帮助信息
man test
#编辑iftest2
vi iftest2
#查看iftest2内容
cat iftest2
#!/bin/bash
#iftest2
echo -n "Enter your name:"
read NAME
#did the user just hit return
if [ "$NAME" == "" ];
then
        echo "You did not enter any infomation"
else
        echo "Your name is ${NAME}"

#改变权限
chmod 755 iftest2
#执行
[root@localhost 0410]# ./iftest2 
Enter your name:ChinaItlab
Your name is ChinaItlab
[root@localhost 0410]# ./iftest2
Enter your name:
You did not enter any information

#新建ifcp
vi ifcp
#查看ifcp内容
[root@localhost 0410]# cat ifcp 
#!/bin/bash
#ifcp
if cp myfile.bak myfile;
then
        echo "good copy"
else
        echo "`basename $0`:error could not copy the files" >&2
fi
#改变权限
chmod 755 ifcp
#执行
[root@localhost 0410]# ./ifcp 
cp: cannot stat `myfile.bak': No such file or directory
ifcp:error could not copy the files



#新建ifelif
vi ifelif
#改变权限
chmod 755 ifelif
#查看ifelif内容
[root@localhost 0410]# cat ifelif 
#!/bin/bash
#ifelif
echo -n "Enter your name:"
read NAME
if [ -z $NAME ] || [ "$NAME" = "" ];
then
        echo "You did not enter a name."
elif [ "$NAME" = "root" ];
then
        echo "Hello root"
elif [ "$NAME" = "chinaitlab" ];
then
        echo "Hello chinaitlab"
else
        echo "You are not root or wgb,but hi,$NAME"
fi
#执行
[root@localhost 0410]# ./ifelif 
Enter your name:jike
You are not root or wgb,but hi,jike
[root@localhost 0410]# ./ifelif 
Enter your name:root
Hello root
[root@localhost 0410]# ./ifelif 
Enter your name:chinaitlab
Hello chinaitlab
[root@localhost 0410]# ./ifelif 
Enter your name:
You did not enter a name.

#vi编辑时设置行号
:set nu


#case语句
#新建caseselect
vi caseselect
#改变权限
chmod 755 caseselect
#查看caseselect内容
[root@localhost 0410]# cat caseselect 
#!/bin/bash
#case select
echo -n "Enter a number from 1 to 3:"
read ANS
case $ANS in
1)
        echo "You select 1"
;;
2)
        echo "You select 2"
;;
3)
        echo "You select 3"
;;
*)
        echo "`basename $0`:This is not between 1 and 3" >&2
        exit;
;;
esac
#执行
[root@localhost 0410]# ./caseselect 
Enter a number from 1 to 3:45
caseselect:This is not between 1 and 3
[root@localhost 0410]# ./caseselect 
Enter a number from 1 to 3:2
You select 2
[root@localhost 0410]# ./caseselect 
Enter a number from 1 to 3:3
You select 3

#重新修改，然后查看内容
[root@localhost 0410]# cat caseselect 
#!/bin/bash
#case select
echo -n "Enter a number from 1 to 3:"
read ANS
case $ANS in
1)
        echo "You select 1"
;;
2)
        echo "You select 2"
;;
3)
        echo "You select 3"
;;
y|Y)
        echo "You select $ANS"
;;
*)
        echo "`basename $0`:This is not between 1 and 3" >&2
        exit;
;;
esac
#执行
[root@localhost 0410]# ./caseselect 
Enter a number from 1 to 3:Y
You select Y
[root@localhost 0410]# ./caseselect 
Enter a number from 1 to 3:y
You select y


#for循环
#新建forlist1
vi forlist1
#查看forlist1内容
[root@localhost 0410]# cat forlist1
#!/bin/bash
#forlist1
for loop in 1 2 3 4 5
do
        echo $loop
done
#改变权限
[root@localhost 0410]# chmod 755 forlist1
#执行
[root@localhost 0410]# ./forlist1 
1
2
3
4
5
#将执行结果重定向到list.txt
[root@localhost 0410]# ./forlist1 >list.txt
#查看list.txt内容
[root@localhost 0410]# cat list.txt 
1
2
3
4
5

#新建forlist2
vi forlist2
#查看forlist2内容
 [root@localhost 0410]# cat forlist2
#!/bin/bash
#forlist2
#有双引号
for loop in "orange red bue grey"
do
        echo $loop
done
#改变权限
[root@localhost 0410]# chmod 755 forlist2
#执行
[root@localhost 0410]# ./forlist2 
orange red bue grey

#拷贝文件
cp forlist2 forlist3
#编辑forlist3
vi forlist3
#查看forlist3内容
[root@localhost 0410]# cat forlist3
#!/bin/bash
#forlist2
#没有双引号
for loop in orange red bue grey
do
        echo $loop
done
#执行
[root@localhost 0410]# ./forlist3
orange
red
bue
grey

#拷贝文件
cp forlist2 forlist4
#编辑forlist4
vi forlist4
#新建myfile
vi myfile
#查看forlist4内容
[root@localhost 0410]# cat forlist4
#!/bin/bash
#forlist2
for loop in `cat myfile`
do
        echo $loop
done
#执行forlist4
[root@localhost 0410]# ./forlist4
parm
findfile
#查看myfile内容
[root@localhost 0410]# cat myfile 
parm
findfile
#编辑myfile
vi myfile
#重新查看
[root@localhost 0410]# cat myfile 
parm 1 2
findfile
#执行
[root@localhost 0410]# ./forlist4
parm
1
2
findfile
#说明是以空格或者换行作为划分的


#until循环
#新建until_mon
vi until_mon
#查看until_mon内容
[root@localhost 0410]# cat until_mon 
#!/bin/s
#until_mon
#监控分区
Part="/backup"
#得到磁盘使用的百分比
LOOK_OUT=`df|grep "$Part"|awk '{print $5}'|sed 's/%//g'`
echo $LOOK_OUT
until [ "$LOOK_OUT"-gt"90" ]
do
        echo "Filesystem /backup is nearly full" |mail root
done
#改变权限
chmod 755 until_mon
#执行
[root@localhost 0410]# ./until_mon

#重新编辑until_mon
vi until_mon
#后台执行until_mon
nohup ./until_mon
#查看until_mon
[root@localhost 0410]# cat until_mon 
#!/bin/sh
#until_mon
#监控分区
Part="/backup"
#得到磁盘使用的百分比
LOOK_OUT=`df|grep "$Part"|awk '{print $5}'|sed 's/%//g'`
echo $LOOK_OUT
until [ "$LOOK_OUT"-gt"90" ]
do
        echo "Filesystem /backup is nearly full" |mail root
        LOOK_OUT=`df|grep "$Part"|awk '{print $5}'|sed 's/%//g'`
        sleep 3600
done

#while循环
#新建whileread
vi whileread
#改变权限
chmod 755 whileread
#改变权限
[root@localhost 0410]# chmod 755 whileread
#查看whileread
[root@localhost 0410]# cat whileread
#!/bin/sh
#whileread
echo "按住<crtl>+D退出输入。"
while echo -n "输入你最喜欢的电影:";
read FILM
do
        echo "Yeah,${FILM}是一部好电影!"
done
#执行
[root@localhost 0410]# ./whileread 
按住<crtl>+D退出输入。
输入你最喜欢的电影:KAT 
Yeah,KAT是一部好电影!
输入你最喜欢的电影:KAT
Yeah,KAT是一部好电影!
输入你最喜欢的电影:KAT
Yeah,KAT是一部好电影!
输入你最喜欢的电影:

#新建whilereadline
vi whilereadline
#查看whilereadline
cat whilereadline
#修改权限
chmod 755 whilereadline
#查看names.txt，没有改文件
[root@localhost 0410]# cat names.txt
cat: names.txt: No such file or directory
#重新查看，已输入内容
[root@localhost 0410]# cat names.txt
shenzhen
shangha
beijing
#查看whilereadline内容
[root@localhost 0410]# cat whilereadline
#!/bin/sh
#whileraad
while read LINE
do
        echo $LINE
done < names.txt
#执行
[root@localhost 0410]# ./whilereadline 
shenzhen
shangha
beijing

#拷贝文件
cp whilereadline whilereadline2
#编辑whilereadline2
vi whilereadline2
#查看whilereadline2内容
[root@localhost 0410]# cat whilereadline2
#!/bin/sh
#whileraad
while read LINE <names.txt
do
        echo $LINE
done
#执行
./whilereadline2
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen
shenzhen

#break和continue控制
#新建breakout
vi breakout
#改变权限
[root@localhost 0410]# chmod 755 breakout
#查看breakout内容
[root@localhost 0410]# cat breakout 
#!/bin/bash
#breakout
while :
do
        echo -n "Enter any number[1...5]:"
        read ANS
        case $ANS in
        1|2|3|4|5)
                echo "You enter a number between 1 and 5."
                ;;
        *)
                echo "Wrong number,Bye."
                break;
                ;;
        esac
done
#执行
[root@localhost 0410]# ./breakout 
Enter any number[1...5]:4
You enter a number between 1 and 5.
Enter any number[1...5]:3
You enter a number between 1 and 5.
Enter any number[1...5]:54
Wrong number,Bye.

#拷贝文件
cp breakout breakout2
#新建breakout2
vi breakout2
#查看breakout2内容
[root@localhost 0410]# cat breakout2
#!/bin/bash
#breakout
while :
do
        echo -n "Enter any number[1...5]:"
        read ANS
        case $ANS in
        1|2|3|4|5)
                echo "You enter a number between 1 and 5."
                ;;
        *)
                echo -n "Wrong number,continue(y/n)?:"
                read IS_CONTINUE
                case $IS_CONTINUE in
                        y|yes|Y|Yes)
                                continue
                                ;;
                        *)
                                break;
                                ;;
                esac:
        esac
done
#执行
[root@localhost 0410]# ./breakout2
Enter any number[1...5]:1
You enter a number between 1 and 5.
Enter any number[1...5]:3
You enter a number between 1 and 5.
Enter any number[1...5]:3
You enter a number between 1 and 5.
Enter any number[1...5]:56
Wrong number,continue(y/n)?:y
Enter any number[1...5]:432
Wrong number,continue(y/n)?:n
[root@localhost 0410]# ./breakout2
Enter any number[1...5]:5
You enter a number between 1 and 5.
Enter any number[1...5]:45
Wrong number,continue(y/n):yes
Enter any number[1...5]:n

附图

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