今天再來學習shell腳本，下面對自己已經掌握的一些shell語法及命令進行總結！
1.read命令提示用戶輸入字符串
設置好PATH變量，這個比較好的是我們寫的腳本在執行時可以直接使用一些外部命令，而不必加上絕對路徑。
[zoulei@CentOS test]$ vim test.sh
1 #!/bin/bash
2 PATH=$PATH
3 export PATH
4 read -p "Your first name:" firstname
5 read -p "Your last name:" lastname
6 echo -e "Your full name：$firstname $lastname"
7 exit 0[zoulei@CentOS test]$ sh test.sh
Your first name:zou
Your last name:lei
Your full name：zou lei
[zoulei@CentOS test]$ echo $?
0exit 0的作用是離開script且執行完腳本的同時回傳一個0給系統，然後在shell命令行輸入echo $?則可得到0的值。
2.test命令的測試功能
[zoulei@CentOS test]$ vim test.sh
1 #!/bin/bash
2 PATH=$PATH
3 export PATH
4 echo -e "Input name of the file that you want to check"
5 read -p "Filename:" filename
6 test -z $filename && echo "You must input a filename" && exit 0
7 test ! -e $filename && echo "The file '$filename' DO NOT exist" && exit 0
8 exit 0[zoulei@CentOS test]$ sh test.sh
Input name of the file that you want to check
Filename:test.sh
[zoulei@CentOS test]$ sh test.sh
Input name of the file that you want to check
Filename:hh.sh
The file 'hh.sh' DO NOT exist
[zoulei@CentOS test]$test -e filename表示filename文件是否存在，
test ! -x filename表示當filename不具有X時，回傳ture!這裏的x指e,f,d等測試標誌，x爲e用看來測試文件是否存在！
3.條件表達式
（1）if...elif..else...fi結構
[zoulei@CentOS test]$ vim test.sh
1 #!/bin/bash
2 PATH=$PATH
3 export PATH
4 read -p "Please input [Y/N]" choice
5 if [ "$choice" == "Y" ] || [ "$choice" == "y" ];then
6 echo "OK!continue"
7 exit 0
8
9 elif [ "$choice" == "N" ] || [ "$choice" == "n" ];then
10 echo "oh!interupt"
11 exit 0
12 else
13 echo "Input [Y/N]"
14 fi
15 exit 0
16[zoulei@CentOS test]$ vim test.sh
[zoulei@CentOS test]$ sh test.sh
Please input [Y/N]y
OK!continue
[zoulei@CentOS test]$ sh test.sh
Please input [Y/N]n
oh!interupt
[zoulei@CentOS test]$
[zoulei@CentOS test]$ vim test.sh
[zoulei@CentOS test]$ sh test.sh
Please input [Y/N]y
OK!continue
[zoulei@CentOS test]$ sh test.sh
Please input [Y/N]n
oh!interupt
[zoulei@CentOS test]$ sh test.sh
Please input [Y/N]k
Input [Y/N]
[zoulei@CentOS test]$
[zoulei@CentOS test]$ vim test.sh
1 #!/bin/bash
2 PATH=$PATH
3 export PATH
4 read -p "Please input your choice:" choice
5 case $choice in
6 "one")
7 echo "Your choice is ONE"
8 ;;
9 "two")
10 echo "Your choice is TWO"
11 ;;
12 "three")
13 echo "Your choice is THREE"
14 ;;
15 *)
16 echo "Usage $0{one|two|three}"
17 ;;
18 esac
19 exit 0*************************************************************************************************************************************************************************************
注意：
case結構語法如下：case $變量名稱 in <==關鍵字爲case,變量前有$符號
"第一個變量名稱"）
；； <==每個類型結尾使用兩個連續的分號來處理！
"第二個變量名稱"）
；；
*） <==最好一個變量的內容都會用*來代表其他值
esac <==最終的case結尾！“case反過來寫表示結尾”
**************************************************************************************************************************************************************************************
[zoulei@CentOS test]$ sh test.sh
Please input your choice:one
Your choice is ONE
[zoulei@CentOS test]$ sh test.sh
Please input your choice:kk
Usage test.sh{one|two|three}
[zoulei@CentOS test]
**************************************************************************************************************************************************************************************
注意：
($0,$1...)爲shell script 的默認變量，$0表示執行的腳本文件名，$1表示腳本文件名後接的第一個參數，$2表示腳本文件名後接的第二個參數。$#代表腳本文件名後接的參數個數，$@代表"$1","$2","$3"之意，每個變量是獨立的。
**************************************************************************************************************************************************************************************
4.循環
(1)while...do...done結構
[zoulei@CentOS test]$ vim test.sh
1 #!/bin/bash
2 PATH=$PATH
3 export PATH
4
5 while [ "$choice" != "yes" ]
6 do
7 read -p "Give your choice [yes/no]:" choice
8 done
9 echo "OK! you input the correct answer"
10 exit 0
[zoulei@CentOS test]$ sh test.sh
Give your choice [yes/no]:no
Give your choice [yes/no]:yes
OK! you input the correct answer
[zoulei@CentOS test]$
（2）for...do...done結構
[zoulei@CentOS test]$ vim test.sh
1 #!/bin/bash
2 PATH=$PATH
3 export PATH
4
5 for animal in cat dog elephant
6 do
7 echo "There are ${animal}s..."
8 done
9 #echo "OK! you input the correct answer"
10 exit 0
[zoulei@CentOS test]$ sh test.sh
There are cats...
There are dogs...
There are elephants...
注意:
語法爲：
for var in con1 con2 con3 ...
do
程序段
done
這個$var的變量內容在循環工作時：1.第一次循環時，$var的內容爲con1;2.第二次循環時，$var的內容爲con2；3.第三次循環時，$var的內容爲con3；......
****************************************************************************************************************************************************************************************************
再看個例子：
[zoulei@CentOS test]$ vim test.sh
1 #!/bin/bash
2 PATH=$PATH
3 export PATH
4 users=$(cut -d ':' -f1 /etc/passwd)
5
6 for username in $users
7 do
8 id $username
9
10 done
11
12 exit 0
[zoulei@CentOS test]$ sh test.sh
uid=0(root) gid=0(root) 組=0(root)
uid=1(bin) gid=1(bin) 組=1(bin),2(daemon),3(sys)
uid=2(daemon) gid=2(daemon) 組=2(daemon),1(bin),4(adm),7(lp)
uid=3(adm) gid=4(adm) 組=4(adm),3(sys)
uid=4(lp) gid=7(lp) 組=7(lp)
uid=5(sync) gid=0(root) 組=0(root)
uid=6(shutdown) gid=0(root) 組=0(root)
uid=7(halt) gid=0(root) 組=0(root)
uid=8(mail) gid=12(mail) 組=12(mail)
uid=10(uucp) gid=14(uucp) 組=14(uucp)
uid=11(operator) gid=0(root) 組=0(root)
uid=12(games) gid=100(users) 組=100(users)
uid=13(gopher) gid=30(gopher) 組=30(gopher)
uid=14(ftp) gid=50(ftp) 組=50(ftp)
uid=99(nobody) gid=99(nobody) 組=99(nobody)
uid=81(dbus) gid=81(dbus) 組=81(dbus)
uid=113(usbmuxd) gid=113(usbmuxd) 組=113(usbmuxd)
uid=69(vcsa) gid=69(vcsa) 組=69(vcsa)
uid=499(rtkit) gid=497(rtkit) 組=497(rtkit)
uid=170(avahi-autoipd) gid=170(avahi-autoipd) 組=170(avahi-autoipd)
uid=498(pulse) gid=496(pulse) 組=496(pulse)
uid=68(haldaemon) gid=68(haldaemon) 組=68(haldaemon)
uid=38(ntp) gid=38(ntp) 組=38(ntp)
uid=48(apache) gid=48(apache) 組=48(apache)
uid=497(saslauth) gid=76(saslauth) 組=76(saslauth)
uid=89(postfix) gid=89(postfix) 組=89(postfix),12(mail)
uid=173(abrt) gid=173(abrt) 組=173(abrt)
uid=42(gdm) gid=42(gdm) 組=42(gdm)
uid=74(sshd) gid=74(sshd) 組=74(sshd)
uid=72(tcpdump) gid=72(tcpdump) 組=72(tcpdump)
uid=500(lingyun) gid=500(lingyun) 組=500(lingyun)
uid=32(rpc) gid=32(rpc) 組=32(rpc)
uid=29(rpcuser) gid=29(rpcuser) 組=29(rpcuser)
uid=65534(nfsnobody) gid=65534(nfsnobody) 組=65534(nfsnobody)
uid=501(zoulei) gid=501(zoulei) 組=501(zoulei)
uid=502(leilei) gid=502(leilei) 組=502(leilei)5.函數function
[zoulei@CentOS test]$ vim test.sh
1 #!/bin/bash
2 PATH=$PATH
3 export PATH
4 function print(){
5 echo "Your choice is $1"
6 }
7 echo "This program will print your choice! "
8
9 case $1 in
10 "one")
11 print 1
12 ;;
13 "two")
14 print 2
15 ;;
16 "three")
17 print 3
18 ;;
19 *)
20 echo "Usage $0 {one|two|three}"
21 ;;
22 esac
23 exit 0**************************************************************************************************************************************************************************************************
注意：
function語法：
function fname() {
程序段
}
那個fname是我們自定義的執行命令的名稱，程序段就是我們要執行它的內容。
***************************************************************************************************************************************************************************************************
[zoulei@CentOS test]$ sh test.sh two
This program will print your choice!
Your choice is 2相信學習了shell script的這些語法，看懂別人寫的腳本應該是沒有什麼問題了，只要很熟悉shell命令，那麼我相信也能夠寫出自己想要的腳本，不過一切的要自己多去寫才行！
好了，shell 腳本先總結到這裏了！以後自己要多多練習。