The use of for loop (1)

1. Calculate the sum of all integers from 1 to 100

for ((i=1; i<=100;i++))
do
  sum=$[$sum + $i]
done

#!/bin/bash

a=0
for ((i=1; i<=100; i++))
do
  a=$(($a+$i))
done
echo $a

2. Filter out the odd and even numbers of all integers from 1 to 100

#!/bin/bash

for  ((i=1; i<=100; i++))
do
let a=$i%2
if [ $a = 0 ]
  then
    echo -e -n "偶数 $i\t"
else
    echo "奇数 $i"
fi
done

3. Prompt the user to enter an integer less than 100, and calculate the sum of all integers from 1 to this number

#!/bin/bash

read -p "请输入小于100的整数：" num
a=0
 for ((i=1; i<=$num; i++))
   do
 a=$(($a+$i))
   done
echo $a

4. Find the even and odd sums of all integers from 1 to 100

#!/bin/bash

b=0
c=0
for ((i=1; i<=100; i++))
do
let a=$i%2
if [ $a = 0 ]
   then
      let c=$i+$c
elif [ $a = 1 ]
    then
      let b=$i+$b
fi
done
echo "$c 为1到100偶数的和"
echo "$b 为1到100奇数的和"

5. Detect whether the host in the specified range is communicating, and output the communicating host ip to the file host_ip

#!/bin/bash

for i in 192.168.100.{110..113}
do
  ping -c 3 -i 0.5 -W 2 $i
if [ $? = 0 ]
  then
    echo $i >> host_ip
else
    echo "$i offline"
fi
done

6. Output all executable files in the /dev directory

#!/bin/bash

for i in /dev/*
do
if [ -f $i  ]
   then
    echo "$i 文件存在"
 if [ -x $i ]
   then
    echo "$i 有执行权限"
 else
    echo "$i 没有执行权限"
 fi
else
   echo "$i 不是文件"
fi
done

7. Execute the script to enter the user name, if the user exists, the output prompts that the user already exists; if the user does not exist, prompt the user to enter the password, create the user and set up its password

#!/bin/bash

read -p "请输入用户名：" user
useradd $user

if [ $? = 9 ]
  then
   echo "$user 已存在"
  else
read -p "请输入密码：" a
   echo "$a" | passwd --stdin $user
fi