标签：shell控制流结构 until while for break
[本文是自己学习所做笔记，欢迎转载，但请注明出处：http://blog.csdn.net/jesson20121020]
今天开始学一些同其他高级语言一样的shell流控制结构
语句格式：
if condition1 then command1 else condition2 then command2 else command3 fi注：if语句必须以fi终止。
如果没有condition２,则if语句可以简化为如下：
if condition
then
command1
else
command2
fi或：
if condition
then
command1
fi
例子：
if_test.sh
#!/bin/bash #if_test echo -n "please input two number(a and b):" read a b if [ $a -lt $b ] then echo "$a is less than $b" elif [ $a -gt $b ] then echo "$a is greater than $b" else echo "$a ia equal to $b" fi
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ chmod a+rx if_test.sh jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./if_test.sh please input two number(a and b):10 10 10 ia equal to 10 jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./if_test.sh please input two number(a and b):10 12 10 is less than 12 jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./if_test.sh please input two number(a and b):8 2 8 is greater than 2注意，其中用于了比较运算符，更加详细的比较运算符，请参考man test。
语句格式：
case value in
模式１)
command1
;;
模式２)
command2
;;
esac
注意：
１case取值后面必须为单词in，每一模式必须以右括号结束，取值可以为变量或者常数。
2 模式匹配符*表示任意字符；?表示任意单字符；[...]表示类或范围中任意字符。
例子：
case_test.sh
#!/bin/bash
#case_test
echo -n "Enter a number from 1 to 3:"
read n
case $n in
1)
echo "You select 1"
;;
2)
echo "You select 2"
;;
3)
echo "You select 3"
;;
*) echo "You select *"
;;
esac
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ chmod a+rx case_test.sh jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./case_test.sh Enter a number from 1 to 3:1 You select 1 jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./case_test.sh Enter a number from 1 to 3:2 You select 2 jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./case_test.sh Enter a number from 1 to 3:3 You select 3 jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./case_test.sh Enter a number from 1 to 3:* You select * jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./case_test.sh Enter a number from 1 to 3:20 You select *
格式：
for 变量名 in 列表
do
命令１
命令２
done
例子：
for_test1.sh
#!/bin/bash
#for_test
for loop in 1 2 3 4 5
do
echo $loop
done
运行结果：
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./for_test1.sh 1 2 3 4 5for_test2.sh
#!/bin/bash #for_test2 for loop in orange red blue gray do echo $loop done运行结果：
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./for_test2.sh orange red blue grayfor_test3.sh
#!/bin/bash
#for_test3
for loop in `cat name.txt`
do
echo $loop
done 运行结果：
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ cat name.txt jesson cherry jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./for_test3.sh jesson cherry
格式：
until 条件
do
命令
done
until_test.sh
#!/bin/bash
#until_test
i=10
until [ $i -lt 0 ]
do
echo $i
let i=i-1
# ((i=$i-1))
#i=$[i-1]
done 给予权限，执行结果如下：
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ chmod a+rx until_test.sh jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./until_test.sh 10 9 8 7 6 5 4 3 2 1 0
格式：
while 命令
do
命令
.......
done
例子：
while_test1.sh
#!/bin/bash
#while_test1
while echo -n "输入你喜欢的明星:";read Mingxing
do
echo "$Mingxing 是你喜欢的明星"
done 给予权限，执行：
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ chmod a+rx while_test1.sh jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./while_test1.sh 输入你喜欢的明星:周杰 周杰 是你喜欢的明星 输入你喜欢的明星:孙楠 孙楠 是你喜欢的明星while_test2.sh
#!/bin/bash #while_test while read NAME do echo $NAME done <name.txt给予权限，执行：
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ chmod a+rx while_test2.sh jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./while_test2.sh jesson cherry
break [n]
－退出循环
－如果是在一个嵌入循环里，可以指定n来跳出的循环个数。
continue
－跳过循环步
注意，这和其他高级语言中的一样，continue命令类似于break，只有一点差别，它不会跳出循环，而是路过当前循环步。
例子：
break_test.sh
#!/bin/bash
#break_test.sh
while :
do
echo -n "Enter any number(1,...,5):"
read ANS
case $ANS in
1|2|3|4|5)
echo "You enter anumber between 1 and 5"
;;
*)
echo "Wrong number,Bye"
break;
;;
esac
done 给予权限，执行如下：
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ chmod a+rx break_test.sh jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./break_test.sh Enter any number(1,...,5):1 You enter anumber between 1 and 5 Enter any number(1,...,5):2 You enter anumber between 1 and 5 Enter any number(1,...,5):3 You enter anumber between 1 and 5 Enter any number(1,...,5):4 You enter anumber between 1 and 5 Enter any number(1,...,5):5 You enter anumber between 1 and 5 Enter any number(1,...,5):6 Wrong number,Bye
#!/bin/bash
#continue_break_test
while :
do
echo -n "Enter any number(1,...,5):"
read ANS
case $ANS in
1|2|3|4|5)
echo "You enter a number between 1 and 5"
;;
*)
echo -n "Wrong number,continue(y/n)?:"
read IS_CONTINUE
case $IS_CONTINUE in
y|yes|Y|Yes)
continue
;;
*)
break
;;
esac
esac
done 同样，给予可执行权限，执行
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ chmod a+rx continue_test.sh jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./continue_test.sh Enter any number(1,...,5):2 You enter a number between 1 and 5 Enter any number(1,...,5):3 You enter a number between 1 and 5 Enter any number(1,...,5):4 You enter a number between 1 and 5 Enter any number(1,...,5):5 You enter a number between 1 and 5 Enter any number(1,...,5):8 Wrong number,continue(y/n)?:y Enter any number(1,...,5):1 You enter a number between 1 and 5 Enter any number(1,...,5):79 Wrong number,continue(y/n)?:n
标签：shell控制流结构 until while for break
原文地址：http://blog.csdn.net/jesson20121020/article/details/43032107
