1+2+..+100求和

+--------------+
|   for循环    |
+--------------+
sum=0
for((i=1;i<=100;i++))
do
sum=$((i+$sum))
done
echo $sum

+--------------+
|   while循环  |
+--------------+
sum=0
i=1
while ((i<=100))
do
((sum+=i))
((i++))
done
echo $sum
 
+--------------+
|   数学公式    |
+--------------+
i=100
echo $((sum=i*(i+1)/2))

+--------------+
|     awk      |
+--------------+
seq 100 | awk '{i+=$1}END{print i}'

批量生成8位随机数文件

for((i=1;i<=10;i++))
do
  touch `echo $RANDOM | md5sum | cut -c 1-8`.txt
done

批量修改文件名

ll
-rw-r--r-- 1 root root  0 Jul 31 06:57 01508427.txt
-rw-r--r-- 1 root root  0 Jul 31 06:57 177ad50a.txt
-rw-r--r-- 1 root root  0 Jul 31 06:57 764f1747.txt
-rw-r--r-- 1 root root  0 Jul 31 06:57 79205720.txt
-rw-r--r-- 1 root root  0 Jul 31 06:57 8d54c065.txt
-rw-r--r-- 1 root root  0 Jul 31 06:57 97026f8e.txt

+--------------+
|     sed      |
+--------------+
for i in `ls *.txt`
do
  mv $i `echo $i | sed "s@txt@sh@g"`
done

+--------------+
|     awk      |
+--------------+
for i in `ls *.txt`
do
awk -F. '{print "mv "$0,$1".sh"}'
done

+--------------+
|   rename     |
+--------------+
for i in `ls *.txt`
do
  rename ".txt" ".sh" $i;
done

关闭服务开机自启

chkconfig --list | grep 3:on | awk '{print $1}' | \
egrep -v "rsyslog | sshd | sysstst" | sed -r 's@(.*)@chkconfig \1 off@g' | bash

批量生成用户并设置随机数密码

for i in `seq 10`
do
  RAND=`openssl rand -hex 10`
  useradd test$i && \
  echo $RAND | passwd --stdin test$i && \
  echo -e "user: test$i \t passwd: $RAND" >> /tmp/user.log
done

判断网段IP在线情况

for i in `seq 254`
do
  ping -c2 172.16.100.$i &> /dev/null
  [ $? -eq 0 ] && echo "172.16.100.$i is up" >> /tmp/ip_up.log \
  || echo "172.16.100.$i is down" >> /tmp/ip_down.log
done

利用数组输出IP

array=(
  10.0.0.1
  10.0.0.2
  10.0.0.3
  10.0.0.4
)
for ip in ${array[*]}
do 
  echo $ip
done

-----------

for ((i=0;i<${#array[@]};i++))
do 
  echo ${array[i]}
done