Linux学习笔记之一 ---Shell语法（2）

首先说明一个跟变量比较相关的问题：

eg：read readTestif [  $readTest = "yes" ]

  如果用户直接回车，将会报错 可能是[: =: Unary operator expected 这是为什么呢，因为对对readTest进行比较时， 它是一个空值

从而出现 if [  = "yes" ] 这不是个合法的条件，好方法就是

if [ "$readTest" = "yes" ]//这样就算是空字符串，也是合法的了if [ "" = "yes" ] 

继续记录跟shell语法相关的

2.4 控制语句、

 3）for语句

 for variable in values

do

statements

done

eg：

#!/bin/shfor boo in bar fud 43doecho $boodoneexit0

这样将输出 bar fud 43

4） while 语句

while condition 

do

statements

done

eg：

#!/bin/shecho "Enter password"read trythiswhile [ "$trythis" != "secret" ]; doecho "Sorry, try again"read trythisdoneecho "password is correct"exit 0

5）until 语句

   until condition
do
statements
done

eg：

#!/bin/shuntil who | grep "$1" >/tmp/nulldosleep 60done#now ring the bell and announce the expected userecho -e '\a'echo "*********$1 has juse logged in ********"exit 0

6) case 语句

case variable in
pattern [ |pattern] ...) statements;;
pattern [ |pattern] ...) statements;;
....
esac

eg1：

#!/bin/shecho "Is it morning? Please anser yes or no"read timeofdaycase "$timeofday" inyes) echo "Good Morning";;no ) echo "Good Afternoon";;y  ) echo "Good Morning";;*  ) echo "sorry, anser not recognized";;esacexit 0

eg2

#!/bin/shecho "Is it morning? Please anser yes or no"read timeofdaycase "$timeofday" inyes | y | Yes | YES ) echo "Good Morning";;n*  |N*)  echo "Good Afternoon";;esacexit 0

2.5 函数

function_name () {
statements
}

eg1：

#!/bin/shfoo() { echo "Function foo is executing"}echo "scripot starting"fooecho "scripot ended"exit 0

eg2: 从函数中返回一个值

#!bin/shyes_or_no() {echo "Is your name $* ?"while truedoecho -n "Enter yes or no:"read Xcase "$X" iny | yes ) return 0;;n | no  ) return 1;;*) echo "Anser yes or no";;esacdone}echo "Original parameters are $*"if yes_or_no "$1"thenecho "Hi $1, nice name"elseecho "Nerver mind"fiexit 0

$./my_name Rick Neil
Original parameters are Rick Neil
Is your name Rick?
Enter yes or no: yes
Hi Rick,nice name

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