【if-while-case-for-until】控制流结构

【控制流结构】 --空命令永远为真
 
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if 


   elif 
 else

 fi

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copyfile:
 
#!/bin/sh
#copyfile
if cp surfile desfile.bak
 then echo "haved copy"
else
 echo "`basename $0`:error could not copy the files">%2
fi
 
$ sh copyfile
 haved copy
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#!/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
fi
 
$ 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
 
if [ $# -lt 3] 调用传入脚本的参数个数小于3
 
if [ -t ] 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
 
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========================
case [value] in







esac
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    *   任意字符。
    ?   任意单字符。
    [..]    类或范围中任意字符
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#!/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
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========================
for varname in list
do
 command1
 command2
 ...
done
========================
#!/bin/sh
#text
for loop in 1 2 3 4 5
do
 echo $loop
done
 
$ sh text
1
2
3
4
5
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for loop in "orange red blue grey"
do echo $loop ; done       打印字符串列表
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for loop in `ls`
do echo $loop ; done       打印当前ls的内容
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========================
for varname in list1
 do
  for 




 done
done
========================
until format:
until condition



done
========================
while command
 do



done
========================
#!/bin/sh
#text
count=0
while [ $count -lt 5 ]
do
 count=`expr $count + 1 `
 echo $count
done
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#!/bin/sh
#text
echo -n "enter your most liked film"
while read film
do
 echo "Yeah,great film the $film"
done
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