linux shell程序

• shell程序介绍

　　1.查看我们的Linux（centos6.5为例）有多少我们可以使用的shell：

[root@localhost bin]# cat /etc/shells 
/bin/sh
/bin/bash
/sbin/nologin
/bin/dash
/bin/tcsh
/bin/csh

　　系统某些服务在运作过程中，会去检查使用者能够使用的shells，而这些shell的查询就是由/etc/shells这个档案。

　　2.当我们登入Linux系统的时候，系统就会给我一个shell来工作，而这个登录取得的shell就记录在/etc/passwd这个档案里:

[root@localhost bin]# cat /etc/passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin
adm:x:3:4:adm:/var/adm:/sbin/nologin
...

　　 3.shell的内部指令type，查看指令来自外部指令还是内建在bash当中。

[root@localhost bin]# man cd
[root@localhost bin]# type cd
cd is a shell builtin
[root@localhost bin]# type -t cd
builtin  #表示该指令为bash内建的指令功能
[root@localhost bin]# type -a cd
cd is a shell builtin
[root@localhost bin]# type type
type is a shell builtin
[root@localhost bin]# type it ls
alias  #表示该指令为命名别名所设定的名称
[root@localhost bin]# type uname
uname is hashed (/bin/uname)
[root@localhost bin]# type -t uname
file   #表示为外部指令

　　4.变量的取用 echo

[root@localhost bin]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin
[root@localhost bin]# echo ${PATH}
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

　　变量的设定 = ，如果一个变量未设定，内容为空

[root@localhost bin]# echo $myname

[root@localhost bin]# myname=tian
[root@localhost bin]# echo $myname
tian

　　子程序，就是在目前这个shell的情况下，去启用另一个新的shell，新的shell就是子程序。在一般状态下，父程序的自定义变量无法在子程序内使用，但是通过export将变量变成环境变量，就能在子程序下应用了。

[root@localhost bin]# echo $name
yes
[root@localhost bin]# bash  #进入所谓的子程序
[root@localhost bin]# echo $name

[root@localhost bin]# exit  #离开子程序
exit
[root@localhost bin]# export name
[root@localhost bin]# bash
[root@localhost bin]# echo $name
yes
[root@localhost bin]# exit

　　5.变量的设定规则：

　　6.环境变量

　　env，environment的简写，列出所有的环境变量

[root@localhost /]# env
HOSTNAME=localhost.localdomain
SHELL=/bin/bash
TERM=xterm
HISTSIZE=1000
USER=root
...

　　set，观察所有变量（包含环境变量和自定义变量）

[root@localhost /]# set
BASH=/bin/bash
BASH_VERSINFO=([0]="4" [1]="1" [2]="2" [3]="1" [4]="release" [5]="i386-redhat-linux-gnu")
BASH_VERSION='4.1.2(1)-release'
HISTFILE=/root/.bash_history
HISTFILESIZE=1000
HISTSIZE=1000
HOSTTYPE=i386
OLDPWD=/
OSTYPE=linux-gnu
PPID=5200
PS1='[u@h W]$ '
...

 　　PS1：提示字符的设定

[root@localhost php]# PS1='[u@h w]$'
[root@localhost /usr/local/php]#ls

 　　$变量，代表的是目前这个shell的线程代号，即PID（Process ID）

[root@localhost /]#echo $$
2840

 　　?变量：上一个执行的指令所回传的值，如果执行成功，则回传一个0值，否则，就会回传错误代码（一般为非0值）

[root@localhost scripts]# ls
sh01.sh  sh02-1.sh  sh02.sh  sh03.sh  sh04.sh
[root@localhost scripts]# echo $?
0

　　7.数据流重导向

　　数据流重导向可以将standard output与standard error output分别传送到其他档案或装置去，而分别传送所用的特殊字符则如下所示：

[tianxintian22@localhost ~]$ find /home -name .bashrc 
find: `/home/w002': Permission denied      <==Standard error
/home/tianxintian22/.bashrc                <==Standard output
find: `/home/w001': Permission denied      <==Standard error

#将stdout与stderr分别存到不同的档案
[tianxintian22@localhost ~]$ find /home -name .bashrc > list_right 2> list_error
[tianxintian22@localhost ~]$ ls
Desktop  Documents  Downloads  list_error  list_right  Music  Pictures  Public  Templates  Videos

#将错误数据丢弃，屏幕显示正确的数据
#/dev/null 垃圾桶黑暗装置，可以吃掉任何导向这个装置的信息
[tianxintian22@localhost ~]$ find /home -name .bashrc 2> /dev/null 
/home/tianxintian22/.bashrc

#将指令的数据全部写入list档案中
[tianxintian22@localhost ~]$ find /home -name .bashrc > list 2>&1
#[tianxintian22@localhost ~]$ find /home -name .bashrc &> list   这句等同于上一句
[tianxintian22@localhost ~]$ ls
Desktop  Documents  Downloads  list  list_error  list_right  Music  Pictures  Public  Templates  Videos
[tianxintian22@localhost ~]$ cat list
find: `/home/w002': Permission denied
/home/tianxintian22/.bashrc
find: `/home/w001': Permission denied

• shell script

　　1.路径与指令搜寻顺序

　　2.script指令下达

 　　以上方式下达脚本时，script都会使用一个新的bash环境来执行脚本内的指令，也就是说，script是在子程序的bash内执行的。

　　3.指令依序执行关系

#不清楚/tmp/abc是否存在，但是要建立/tmp/abc/hehe档案
[root@localhost ~]ls /tmp/abc || mkdir /tmp/abc && touch /tmp/abc/hehe

　　4.test指令的测试功能

[root@localhost scripts]# ls
sh01.sh  sh02-1.sh  sh02.sh  sh03.sh  sh04.sh
[root@localhost scripts]# test -e sh01.sh  #该档名是否存在
[root@localhost scripts]# echo $?
0
[root@localhost scripts]# test -f sh01.sh  #该档名是否存在且为档案（file）
[root@localhost scripts]# echo $?
0
[root@localhost scripts]# test -d sh01.sh  #该文件名是否存在且为目录
[root@localhost scripts]# echo $?
1
[root@localhost scripts]# test -d ~/scripts
[root@localhost scripts]# echo $?
0

 　　5.判断符号[ ]

　　编写脚本：sh01.sh

[root@localhost scripts]# vim sh01.sh 
#!/bin/bash
#Program 
#    This program shows the user's choice
#History
#2016/07/11 tianxintian22 first release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH
read -p "Please input (Y/N)" choice
[ "$choice" == 'Y' -o "$choice" == 'y' ] && echo "OK,continue" && exit 0   # -o 等价于或者（or）
[ "$choice" == 'n' -o "$choice" == 'N' ] && echo "Oh,interrupt" && exit 0
echo "I don't know what your choice is" && exit 0

　　执行脚本：

[root@localhost scripts]# sh sh01.sh 
Please input (Y/N)Y
OK,continue

　　6.shell script 默认变数（$1,$2...）

[root@localhost scripts]# vim sh02.sh 
#!/bin/bash
#program
#    program shows the script name, parameters...
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH
echo "The script name is ==> $0"
echo "Total parameter number is ==> $#"
[ "$#" -lt 2 ] && echo "The number of parameter is less than 2.Stop here." && exit 0
echo "Your whole parameter is ==>'$@'"
echo "The first parameter is ==>$1"
echo "The second parameter is ==>$2"
exit 0

　　执行脚本：

[root@localhost scripts]# ./sh02.sh 
The script name is ==> ./sh02.sh
Total parameter number is ==> 0
The number of parameter is less than 2.Stop here.
[root@localhost scripts]# ./sh07.sh one two
The script name is ==> ./sh02.sh
Total parameter number is ==> 2
Your whole parameter is ==>'one two'
The first parameter is ==>one
The second parameter is ==>two

　　7.条件判断式 if...then

[root@localhost scripts]# vim sh01-1.sh 
#!/bin/bash
#Program 
#    This program shows the user's choice
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH
read -p "Please input (Y/N):" choice
if [ "$choice" == 'Y' ] || [ "$choice" == 'y' ];then
    echo "OK,continue" 
elif [ "$choice" == 'n' ] || [ "$choice" == 'N' ];then
    echo "Oh,interrupt"
else
    echo "I don't know what your choice is"
fi

　　执行脚本：

[root@localhost scripts]# ./sh01-1.sh
Please input (Y/N):n
Oh,interrupt

 　　8.case...esac 判断

[root@localhost scripts]# vim sh02.sh 
#!/bin/bash
#program
#    Show "hello" from $1 by using case...esac
#history
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH
case $1 in
　　"hello")
    　　echo "Hello,how are you?"
    　　;;
    "")
    　　echo "You must input parameter, ex> {$0 someword}"
    　　;;
    *)
    　　echo "Usage $0 {hello}"
    　　;;
esac

　　执行脚本：

[root@localhost scripts]# ./sh02.sh hello
Hello,how are you?
[root@localhost scripts]# ./sh02.sh test
Usage ./sh02.sh {hello}
[root@localhost scripts]# ./sh02.sh 
You must input parameter, ex> {./sh02.sh someword}

 　　9.function功能

[root@localhost scripts]# vim sh02-1.sh 
#!/bin/bash
#program
#    use function to repeat information
#history
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH
function printit(){
    echo -n "Your choice is "
}
echo "This program will print your selection!"
case $1 in
    "one")
        printit;echo $1 | tr 'a-z' 'A-Z'
        ;;
    "two")
        printit;echo $1 | tr 'a-z' 'A-Z'
        ;;
    "three")
        printit;echo $1 | tr 'a-z' 'A-Z'
        ;;
    *)
        echo "Usage $0 {one|two|three}"
        ;;
esac

　　执行脚本：

[root@localhost scripts]# ./sh02-1.sh 
This program will print your selection!
Usage ./sh02-1.sh {one|two|three}
[root@localhost scripts]# ./sh02-1.sh one
This program will print your selection!
Your choice is ONE

 shell script 的执行方式是由上而下，由左而右，因此在shell script当中的设定一定要写在程序的最前面！

[root@localhost scripts]# vim sh02-2.sh 
#!/bin/bash
#program
#    use function to repeat information
#history
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH
function printit(){
    echo "Your choice is $1"
}
echo "This program will print your selection!"
case $1 in
    "one")
        printit 1 
        ;;
    "two")
        printit 2
        ;;
    "three")
        printit 3
        ;;
    *)
        echo "Usage $0 {one|two|three}"
        ;;
esac

　　执行脚本：

[root@localhost scripts]# ./sh02-2.sh 
This program will print your selection!
Usage ./sh02-2.sh {one|two|three}
[root@localhost scripts]# ./sh02-2.sh one
This program will print your selection!
Your choice is 1

 　　10.while do done;until do done

#当condition条件满足时，就进行循环
while [ condition ]
do 
    程序语句
done

#当condition条件成立时，终止循环
until [ condition ]
do 
    程序语句
done

　　计算1+2+3+4+...+100：

#!/bin/bash
#program calculate '1+2+3+4+...+100'
#history ...
sum=0
i=0
while [ "$i" != '100' ]
do
    i=$(($i+1))
    sum=$(($sum+$i))
done
echo "1+2+3+...+100="$sum

#!/bin/bash
#program calculate '1+2+3+4+...+100'
#history
sum=0
i=0
until [ "$i" == '100' ]
do
    i=$(($i+1))
    sum=$(($sum+$i))
done
echo "1+2+3+...+100="$sum

　　11.for do done(固定循环)

for var in con1 con2 con3 ...
do
    程序段
done

　　$var 的变量内容在循环时：第一次循环时，$var的内容为con1；第二次循环时，$var的内容为con2；第三次循环时，$var内容为con3；...

　　eg1:

#!/bin/bash
#program 
#    using for ... loop to print 3 animals
#history
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH
for animal in dog cat elephant
do
    echo "There are ${animal}s..."
done

　　执行脚本：

[root@localhost scripts]# sh sh04.sh 
There are dogs...
There are cats...
There are elephants...

 　　eg2:

#!/bin/bash
users=$(cut -d ':' -f 1 /etc/passwd)
for user in $users
do
    id $user
done

　　执行脚本：

[root@localhost scripts]# sh sh05.sh 
uid=0(root) gid=0(root) groups=0(root)
uid=1(bin) gid=1(bin) groups=1(bin),2(daemon),3(sys)
uid=2(daemon) gid=2(daemon) groups=2(daemon),1(bin),4(adm),7(lp)
uid=3(adm) gid=4(adm) groups=4(adm)
...

　　12.for...do...done

for((初始值;限制值;执行步阶))
do
    程序段
done

[root@localhost scripts]# cat sh06.sh 
#!/bin/bash
#program
#    try do calculate 1+2+3+...+${your_input}
#history
read -p "input a number:" number
sum=0
for((i=1;i<=number;i++))
do
    sum=$(($sum+$i))
done
echo "1+2+3+...+$number="$sum

　　执行脚本：

[root@localhost scripts]# sh sh06.sh 
input a number:100
1+2+3+...+100=5050

 　　13.debug

[root@localhost scripts]# sh -n sh06.sh 
#如果语法没有问题，则不会显示任何信息

[root@localhost scripts]# sh -v sh06.sh  #执行脚本前，现将脚本内容输出到屏幕上
#!/bin/bash
#program
#    try do calculate 1+2+3+...+${your_input}
#history
read -p "input a number:" number
input a number:5
sum=0
for((i=1;i<=number;i++))
do
    sum=$(($sum+$i))
done
echo "1+2+3+...+$number="$sum
1+2+3+...+5=15

[root@localhost scripts]# sh -x sh06.sh #将使用到的script内容显示到屏幕上
+ read -p 'input a number:' number
input a number:5
+ sum=0
+ (( i=1 ))
+ (( i<=number ))
+ sum=1
+ (( i++ ))
+ (( i<=number ))
+ sum=3
+ (( i++ ))
+ (( i<=number ))
+ sum=6
+ (( i++ ))
+ (( i<=number ))
+ sum=10
+ (( i++ ))
+ (( i<=number ))
+ sum=15
+ (( i++ ))
+ (( i<=number ))
+ echo 1+2+3+...+5=15
1+2+3+...+5=15