「学习笔记-Linux」学习Shell Script

学习Shell Script

Table of Contents

• 1 什么是Shell Scipt
  • 1.1 程序书写
  • 1.2 程序执行
• 2 简单Shell练习
  • 2.1 例1 接收用户输入
  • 2.2 例2 按日期建立相似名字的文件
• 3 判断式
  • 3.1 测试文件是否存在
  • 3.2 test常用选项
    • 3.2.1 文件类型
    • 3.2.2 权限
    • 3.2.3 文件新旧比较
    • 3.2.4 整数，字符串，多重条件判断
  • 3.3 使用[]判断
• 4 Shell Script 参数
• 5 条件表达式
  • 5.1 if 结构
  • 5.2 if else 结构
  • 5.3 case
• 6 函数
• 7 循环
  • 7.1 while
  • 7.2 for
• 8 shell script的追踪与Debug

1 什么是Shell Scipt

使用指令和基本程序设计结构写成的程序，可以完成复杂的处理流程

1.1 程序书写

#!/bin/bash
# Program:
# This program shows "Hello Wrold" in your screen.
# History:
# 2013/2/3 on_1y First release

PATH=$PATH
export PATH
echo -e "Hello World!\a\n"
exit 0

• 第一行 #!/bin/bash 说明使用的shell类型,不同shell语法可能不同，所以要说明使用的是哪种shell
• 其它#开始的表示注释,注释一般需要说明
  • 程序功能
  • 版本历史
  • 作者及联系方式
• 设置好PATH变量，以便直接可以调用相应路径下的命令
• 程序主体部分
• exit 0 表示程序执行成功，向环境返回0

1.2 程序执行

• bash $bash sh01.sh #如果用sh sh01.sh而sh又不是指向bash，那么sh01.sh内的语法就会不一致，因为用 #sh去解释了bash语法写的shell script,针对这个程序，如果 #$type sh #得到sh is hashed (/bin/sh) #那么会输出-e Hello world!,而非Hello world!
• $./xxx.sh $chmod +x sh01.sh $./sh01.sh
• source $ source sh01.sh

注：用bash和用source的不同在于，用bash执行时，shell script其实是在在父程序bash下新建了一个 bash子程序，这个子程序中执行，当程序执行完后，shell script里定义的变量都会随子程序的结束而消失， 而用source执行时，是在父程序bash中执行,shell script里定义的变量都还在。

2 简单Shell练习

2.1 例1 接收用户输入

# !/bin/bash
# Program:
# This program is used to read user's input 
# History:
# 2013/2/3 on_1y First release

PATH=$PATH
export PATH
read -p "Your first name:" firstname # tell user to input
read -p "Your last name:" lastname # tell user to input
echo -e "\nYour full name: $firstname $lastname"
exit 0

$ bash sh02.sh
Your first name:Minix
Your last name:007

Your full name: Minix 007

2.2 例2 按日期建立相似名字的文件

# !/bin/bash
# Program:
# This program is used to create files according to date
# History:
# 2013/2/3 on_1y First release

PATH=$PATH
export PATH

# Get filename from user
echo -e "I will use 'touch' to create three files."
read -p "Please input your filename:" tmpfilename

# Prevent the user input [Enter]
# Check whether filename exists or not
filename=${tmpfilename:-"filename"}

# Get the final filename according to date
date1=$(date --date='2 days ago' +%Y%m%d) # date of 2 days ago
date2=$(date --date='1 days ago' +%Y%m%d) # date of yesterday
date3=$(date +%Y%m%d) # date of today
filename1=${filename}${date1}
filename2=${filename}${date2}
filename3=${filename}${date3}

# Create file
touch "$filename1"
touch "$filename2"
touch "$filename3"

exit 0

$ bash sh03.sh
I will use 'touch' to create three files.
Please input your filename:WhoKnows
$ ls W*
WhoKnows20130201  WhoKnows20130202  WhoKnows20130203

3 判断式

3.1 测试文件是否存在

test -e filename会根据filename是否存在返回0或1,再交由echo显示结果

$ test -e sh01.sh  && echo "Exists" || echo "Not exists"
Exists
$ test -e sh0x.sh  && echo "Exists" || echo "Not exists"
Not exists

3.2 test常用选项

3.2.1 文件类型

• -e file :file是否存在
• -f file :file是否存在且为文件
• -d file :file是否存在且为目录

3.2.2 权限

• -r file :file是否有读的权限

3.2.3 文件新旧比较

• -nt file1 file2 : file1 是否比 file2新

3.2.4 整数，字符串，多重条件判断

• -z string: string是否为空

例：输出指定文件类型及属性

# !/bin/bash
# Program:
# This program is used to output type and permission of the target file
# History:
# 2013/2/3 on_1y First release

PATH=$PATH
export PATH

# Get filename from user
echo -e "Input name of the file that you want to check.\n"
read -p "Filename:" filename
test -z $filename && echo "You must input a filename." && exit 0

# Check whether the file exists or not
test ! -e $filename && echo "The file '$filename' DO NOT exists" && exit 0

# Check type and permission of the file
test -f $filename && filetype="regular file"
test -d $filename && filetype="directory"
test -r $filename && perm="readable"
test -w $filename && perm="$perm writable"
test -x $filename && perm="$perm executable"

# Output result
echo "The filename:$filename is a $filetype"
echo "And Permissions are :$perm"

exit 0

$ bash sh04.sh
Input name of the file that you want to check.

Filename:sh01.sh
The filename:sh01.sh is a regular file
And Permissions are :readable writable executable

3.3 使用[]判断

• 测试文件是否存在

$ [ -e "sh01.sh" ] ; echo $?
0
$ [ -e "sh0x.sh" ] ; echo $?
1

• 注意[]内空格必须有
• 这种方法和test的test -e "sho1.sh" ; echo $? 是一致的

4 Shell Script 参数

# !/bin/bash
# Program:
# This program is used to ouput parameter of the shell script
# History:
# 2013/2/3 on_1y First release

PATH=$PATH
export PATH

echo "The script's name is ==> $0"
echo "Total parameter number is ==> $#"

# Check whether number of the parameter is less than 2
[ "$#" -lt 2 ] && echo "The number of parameter is less than 2.Stop here." && exit 0

echo "The whole parameter is ==> '$@'"
echo "The first parameter is ==> $1"
echo "The first parameter is ==> $2"

exit 0

$ bash sh05.sh 1a 2b 3c 4d
The script's name is ==> sh05.sh
Total parameter number is ==> 4
The whole parameter is ==> '1a 2b 3c 4d'
The first parameter is ==> 1a
The first parameter is ==> 2b

注：从以上程序可以看出与参数有关的预设变量如何表示

5 条件表达式

5.1 if 结构

# !/bin/bash
# Program:
# This program is used to show if else expression
# History:
# 2013/2/3 on_1y First release

PATH=$PATH
export PATH

read -p "Please input [Y/N]" choice
if [ "$choice" == "Y" ] || [ "$choice" == "y" ];then
echo "OK, continue"
exit 0
fi
if [ "$choice" == "N" ] || [ "$choice" == "n" ];then
echo "Oh, interupt"
exit 0
fi

exit 0

$ bash sh06.sh
Please input [Y/N]y
OK, continue
$ bash sh06.sh
Please input [Y/N]n
Oh, interupt

5.2 if else 结构

# !/bin/bash
# Program:
# This program is used to show if else expression
# History:
# 2013/2/3 on_1y First release

PATH=$PATH
export PATH

read -p "Please input [Y/N]" choice
if [ "$choice" == "Y" ] || [ "$choice" == "y" ];then
echo "OK, continue"
exit 0
elif [ "$choice" == "N" ] || [ "$choice" == "n" ];then
echo "Oh, interupt"
exit 0
else
echo "Input [Y/N]"
fi

exit 0

5.3 case

# !/bin/bash
# Program:
# This program is used to show case expression
# History:
# 2013/2/3 on_1y First release

PATH=$PATH
export PATH

read -p "Tell me your choice:[1-3]=>" choice
case $choice in
"1")
echo "Your choice is ONE"
        ;;
"2")
echo "Your choice is TWO"
        ;;
"3")
echo "Your choice is THREE"
        ;;
esac

exit 0

$ bash sh08.sh
Tell me your choice:[1-3]=>2
Your choice is TWO
$ bash sh08.sh
Tell me your choice:[1-3]=>1
Your choice is ONE
$ bash sh08.sh
Tell me your choice:[1-3]=>3
Your choice is THREE

6 函数

# !/bin/bash
# Program:
# This program is used to test function
# History:
# 2013/2/3 on_1y First release

PATH=$PATH
export PATH

function myprint(){
echo -n "Your choice is "
}

read -p "Tell me your choice:[1-3]=>" choice
case $choice in
"1")
        myprint;echo "ONE"
        ;;
"2")
        myprint;echo "TWO"
        ;;
"3")
        myprint;echo "THREE"
        ;;
esac


exit 0

$ bash sh09.sh 
Tell me your choice:[1-3]=>1
Your choice is ONE
$ bash sh09.sh 
Tell me your choice:[1-3]=>2
Your choice is TWO
$ bash sh09.sh 
Tell me your choice:[1-3]=>3
Your choice is THREE

7 循环

7.1 while

# !/bin/bash
# Program:
# This program shows while expression
# History:
# 2013/2/3 on_1y First release

PATH=$PATH
export PATH

while [ "$choice" != "yes" ]
do
read -p "Give your choice [yes/no]:" choice
done

exit 0

$ bash sh10.sh 
Give your choice [yes/no]:no
Give your choice [yes/no]:no
Give your choice [yes/no]:nx
Give your choice [yes/no]:yes

7.2 for

# !/bin/bash
# Program:
# This program is used to demo for expression
# History:
# 2013/2/3 on_1y First release

PATH=$PATH
export PATH


for choice in 1 2 3
do
echo "your choice is $choice"
done

exit 0

$ bash sh11.sh
your choice is 1
your choice is 2
your choice is 3

8 shell script的追踪与Debug

• sh -n xx.sh # 语法检查
• sh -x xx.sh # 列出xx.sh的执行过程