當命令或程序語句不在命令行下執行，而是通過一個程序文件來執行時，該程序文件就被稱為Shell腳本。在Shell腳本里內置了很多命令、語句及循環控制，然後將這些命令一次性執行完畢，這種通過文件執行腳本的方式稱為非交互的方式。 Shell腳本語言很適合用於處理純文本型的數據，而Linux系統中幾乎所有的配置文件、日誌文件，以及絕大對數的啟動文件都是純文本類型的文件。

實驗一

利用case語句編寫腳本，滿足下列要求

1.執行create時根據userfile和passfile建立用戶
2.執行delete時根據userfile刪除用戶

1.編寫腳本：

[root@localhost mnt]# vim user_ctrl.sh
#!/bin/bash
read -p “Please input the operation (create or delete ): ” OPERATION

//輸入你要執行的動作

case $OPERATION in
create) //第一種情況：create
read -p “Please input the userfile : ” USERFILE //提示輸入文件
[ -e $USERFILE ] || { //判斷是否存在
echo “$USERFILE is not exist “
exit 1
}
read -p “Please input the passwdfile ： ” PASSFILE
[ -e $PASSFILE ] || {
echo “$PASSFILE is not exist “
exit 1
}
USERLINE=`awk ‘BEGIN{N=0}{N++}END{print N}’ $USERFILE` //計算userfile文件行數
for LINE_NUM in `seq 1 $USERLINE` //利用循環建立
do
USERNAME=`sed -n “${LINE_NUM}p” $USERFILE` //截取userfile文件第一行內容
PASSWORD=`sed -n “${LINE_NUM}p” $PASSFILE` //截取passfile文件第一行內容
useradd $USERNAME //建立用戶
echo $PASSWORD | passwd –stdin $USERNAME
done
;;
delete) //第二種情況：delete
read -p “Please input the userfile ： ” USERFILE
[ -e $USERFILE ] || {
echo “$USERFILE is not exist “
exit 1
}
USERLINE=`awk ‘BEGIN{N=0}{N++}END{print N}’ $USERFILE`
for LINE_NUM in `seq 1 $USERLINE`
do
USERNAME=`sed -n “${LINE_NUM}p” $USERFILE`
userdel -r $USERNAME
done
;;
*) //第三種情況：其餘各種情況
echo Eorror!
;;
esac

2.執行：

[root@localhost mnt]# cat userfile
user1
user2
user3
[root@localhost mnt]# cat passfile
123
456
789
[root@localhost mnt]# sh user_ctrl.sh user
Please input the operation (create or delete ): hello //輸入錯誤動作
Eorror!
[root@localhost mnt]# sh user_ctrl.sh user
Please input the operation (create or delete ): create
Please input the userfile : user //輸入錯誤文件
user is not exist
[root@localhost mnt]# sh user_ctrl.sh user
Please input the operation (create or delete ): create
Please input the userfile : userfile
Please input the passwdfile ： passfile //建立用戶
Changing password for user user1.
passwd: all authentication tokens updated successfully.
Changing password for user user2.
passwd: all authentication tokens updated successfully.
Changing password for user user3.
passwd: all authentication tokens updated successfully.
[root@localhost mnt]# sh user_ctrl.sh user
Please input the operation (create or delete ): delete //刪除用戶
Please input the userfile ： userfile
[root@localhost mnt]# id user1
id: user1: no such user

實驗二

循環

循環執行介紹

將某代碼段重複運行多次，通常有進入循環的條件和退出循環的條件

重複運行次數

循環次數事先已知
循環次數事先未知

常見的循環的命令：for, while, until

for循環

[root@centos7 ~]#help for
for: for NAME [in WORDS … ] ; do COMMANDS; done
Execute commands for each member in a list.
The `for’ loop executes a sequence of commands for each member in a
list of items. If `in WORDS …;’ is not present, then `in “$@”‘ is
assumed. For each element in WORDS, NAME is set to that element, and
the COMMANDS are executed.
Exit Status:
Returns the status of the last command executed.
for ((: for (( exp1; exp2; exp3 )); do COMMANDS; done
Arithmetic for loop.
Equivalent to
(( EXP1 ))
while (( EXP2 )); do
COMMANDS
(( EXP3 ))
done
EXP1, EXP2, and EXP3 are arithmetic expressions. If any expression is
omitted, it behaves as if it evaluates to 1.
Exit Status:
Returns the status of the last command executed.

格式1：
for NAME [in WORDS … ] ; do COMMANDS; done for 變量名 in 列表;do 循環體 done for 變量名 in 列表 do 循環體 done

執行機制：
依次將列表中的元素賦值給「變量名」; 每次賦值後即執行一次循環體; 直到列表中的元素耗盡，循環結束

for循環列表生成方式：

直接給出列表
整數列表：
{start..end}
$(seq [start [step]] end)
返回列表的命令:
$(COMMAND)

使用glob，如：*.sh

變量引用，如：$@每個參數為獨立字符串,$#傳遞給腳本的參數的個數，$*全部參數合為一個字符串

範例：面試題，計算1+2+3+…+100的結果

[root@centos8 ~]#sum=0;for i in {1..100};do let sum+=i;done ;echo sum=$sum
sum=5050
[root@centos8 ~]#seq -s+ 100|bc5050
5050
1
2
3
4

範例：

[root@centos8 ~]#cat /data/scripts/for_sum.sh
#!/bin/bash
sum=0
for i in $* ; do
let sum+=i
done
echo sum=$sum
[root@centos8 ~]#bash /data/scripts/for_sum.sh 1 2 3 4 5 6
sum=21

原創文章，作者：投稿專員，如若轉載，請註明出處：https://www.506064.com/zh-hk/n/226541.html