1.求100以内偶数和
#!/bin/bash
let I=1
let SUM=0
while [ $I -le 100];do
if [ （（$I%2））-eq 0 ]
then
SUM=$(($SUM+$I))
I=$(($I+1))
else
I=$(($I+1))
fi
done
echo "The sum is :$SUM"
2.求三个数中的最大值

#！/bin/bash

echo  "please enter three number:"

read A B C
if [ $A -gt $B ]
then

max=$A
else max=$B
fi

if [ $C -gt $max ]
then

max=$C

fi

echo "The max is $max"

3.显示登录用户时间，用户名
#!/bin/bash
cat /etc/passwd|cut -d:  -f1|grep '^$1\>' ||who |grep $1  &> /dev/null
if [ $? -eq 0 ];then
echo "the user is :$1"
TIME=`who|cut -d- -f2,3|cut -d' ' -f1,2`
COUNT=`who |grep $1 |cut -d' ' -f1|wc -l`
echo "$1 login counts are:$COUNT"
echo "$1 login time is:$TIME"
else
echo "please give me a current name:"
fi
4.ping 一个c类网
 #!/bin/bash
  cping (){
  pingnet=`echo $1 | sed 's/\([0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\).*\1/g'`
  let I=1
   while [ $I -le 254 ];do
   ping -c 1 -W 2 $pingnet.$I &> /dev/null
   [ $? -eq 0 ] && echo "$pingnet.$I online." || echo "$pingnet.$I offline."
   let I++
   done
  }
  read -p "A network:"MYNET
  cping $MYNET
5.判断用户是否存在并显示默认shell
#!/bin/bash
read  -p "please input your username:" A
 if cut -d: -f1 /etc/passwd |grep "^$A$" &> /dev/null;then
B=`grep "$A:"   /etc/passwd | cut -d: -f7`
echo "${A}'s shell is $B." 
 else
   echo " $A not exist,please give me a correct username! "
 fi
6.输入一个文件并统计有多少行
#!/bin/bash
let COUNTS=0

echo "Please enter a file:"FILE

read FILE


if [ -e $FILE -a -f $FILE ];then
 
 while read LINE
 
 do
 
 echo $LINE
 
 COUNTS=$(($COUNTS+1))
 
 done < $FILE
 
 echo "The total linesis $COUNTS."
else
echo  "This FILE is wrong ,please enter a right FILE. "
 
fi

7.定义一个简单的函数，求两个数的大小
#！/bin/bash
max() {
[ $1 -gt $2 ] && echo "The max is $1."||echo "The max is $2."
}
max 1 2