if-while-case-for-until控制流

最新推荐文章于 2024-08-18 12:00:56 发布

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本文介绍了Shell脚本中的控制流结构，包括if条件语句、case选择语句、for循环语句、while循环语句等，并通过具体示例展示了如何使用这些结构来实现逻辑控制。

【控制流结构】 --空命令永远为真

========================

if expresion

then [:]

command1

elif command2

else

command3

command4

========================

copyfile:

#!/bin/sh

#copyfile

if cp surfile desfile.bak

then echo "haved copy"

else

echo "`basename $0`:error could not copy the files">%2

$ sh copyfile

haved copy

----------------------------------------------------

#!/bin/sh

#copyfile

if cp nothisfile desfile.bak >/dev/null 2>&1 --不在屏幕显示

then [:]

echo "haved copy"

else

echo "`basename $0`:error could not copy the files">&2

$ sh copyfile

copyfile:error could not copy the files

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filename=text.txt

if [ ! -w "$filename" ] --判断文件 text.txt 为不可写文件

if [ $# -lt 3] --调用传入脚本的参数个数小于3

if [ -t ] --test返回值为1,则为交互模式(终端模式)

if [ -z $EDITOR ] --环境变量$EDITOR是否为空变量

$ ["$DIRECTORY" = ""] --环境变量$DIRECTORY是否为空变量

if [ -z $LOGNAME ！= "root" ] --登录账户为非root账户

----------------------------------------------------

========================

case [value] in

mod1)

command1

;;

mod2)

command2

;;

……

esac

========================

* 任意字符。

? 任意单字符。

[..] 类或范围中任意字符

----------------------------------------------------

#!/bin/sh

#text

echo -n "Enter a number from 1 to 5 :"

read ANS

case $ANS in

1) echo "You select 1"

;;

2) echo "You select 2"

;;

3) echo "You select 3"

;;

4) echo "You select 4"

;;

5|6) echo "You select 5/6"

;;

yes|y) echo "You select 4"

;;

*) echo "`basename $0 ` : This is not between 1 and 5 ">&2

[break]

exit 1

;;

esac

$ sh text

Enter a number from 1 to 5 :3

You select 3

$ sh text

Enter a number from 1 to 5 :8

text : This is not between 1 and 5

----------------------------------------------------

========================

for varname in list

command1

command2

...

done

========================

#!/bin/sh

#text

for loop in 1 2 3 4 5

echo $loop

done

$ sh text

----------------------------------------------------

for loop in "orange red blue grey"

do echo $loop ; done --打印字符串列表

----------------------------------------------------

for loop in `ls`

do echo $loop ; done --打印当前ls的内容

----------------------------------------------------

========================

for varname in list1

for varname2 in list2

command1

command2

……

done

========================

until format:

until condition

command1

command2

……

done

========================

while command

cammand1

command2

……

done

========================

#!/bin/sh

#text

count=0

while [ $count -lt 5 ]

count=`expr $count + 1 `

echo $count

done

----------------------------------------------------

#!/bin/sh

#text

echo -n "enter your most liked film"

while read film

echo "Yeah,great film the $film"

done

----------------------------------------------------