Shell中的while循环几种使用实例详解

#!/bin/bash
i=1
sum=0
while [ $i -le 100 ]
do
 let sum=sum+$i
 let i++
done
echo $sum

#!/bin/bash
i=1
sum=0
while [ $i -le 100 ]
do
 let sum=sum+$i
 let i+=2
done
echo $sum

#!/bin/bash
i=2
sum=0
while [ $i -le 100 ]
do
 let sum=sum+$i
 let i+=2
done
echo $sum

#!/bin/bash
i=1
j=1
while [ $i -le 5 ]
do
 while [ $j -le 5 ]
 do
   echo -n "* "
   let j++
 done
 echo
 let i++
 let j=1
done

#!/bin/bash
file=$1         #将位置参数1的文件名复制给file
if [ $# -lt 1 ];then   #判断用户是否输入了位置参数
 echo "Usage:$0 filepath"
 exit
fi
while read -r line  #从file文件中读取文件内容赋值给line（使用参数r会屏蔽文本中的特殊符号，只做输出不做转译）
do
 echo $line    #输出文件内容
done  < $file

#!/bin/bash
file=$1
if [[ $# -lt 1 ]]
then
 echo "Usage: $0 please enter you filepath"
 exit
fi
while read -r f1 f2 f3  #将文件内容分为三列
do
 echo "file 1:$f1 ===> file 2:$f2 ===> file 3:$f3"  #按列输出文件内容
done < "$file"

#!/bin/bash
#打印菜单
while :
do
 echo "********************"
 echo "    menu    "
 echo "1.tima and date"
 echo "2.system info"
 echo "3.uesrs are doing"
 echo "4.exit"
 echo "********************"
 read -p "enter you choice [1-4]:" choice
#根据客户的选择做相应的操作
 case $choice in
  1)
  echo "today is `date +%Y-%m-%d`"
  echo "time is `date +%H:%M:%S`"
  read -p "press [enter] key to continue..." Key  #暂停循环，提示客户按enter键继续
  ;;
  2)
  uname -r
  read -p "press [enter] key to continue..." Key
  ;;
  3)
  w
  read -p "press [enter] key to continue..." Key
  ;;
  4)
  echo "Bye!"
  exit 0
  ;;
  *)
  echo "error"
  read -p "press [enter] key to continue..." Key
  ;;
 esac
done