Article Directory
1. for loop
格式：
for 变量 in item1 item2 … itemN
do
语句1
语句2
done
写成一行：
for 变量 in item;do 语句1;语句2 done;
The for statement defines four forms of variables
for var in $(seq 起点 终点 步长)
for var in 1 2 3 ... 10
for var in{
1..10}
for((var=0;var<10;var++))
#无限循环
for (( ; ; ))
Exercise 1:
Script: check_host.sh
detects whether 10 hosts and your current host are directly connected to the host is unblocked, if unblocked, the host ip list will be displayed.
#!/bin/bash
for i in {
1..10}
do
ping -c1 -w1 172.25.254.$i &> /dev/null && {
echo " 172.25.254.$i tongchang !"
}
done
Exercise 2:
Script create.sh
- Automatically create users
- Add user name file and password file after script
- Automatically detect whether the user in the user file exists, and automatically create it if it does not exist, and the password is the content in the corresponding password file
#!/bin/bash
length=`sed -n '$=' user_file`
for LINE in `seq 1 $length`
do
uName=`sed -n ${
LINE}p $1`
uPass=`sed -n ${
LINE}p $2`
id $uName &> /dev/null && {
echo "$uName is exist !"
} || {
useradd $uName
echo $uPass | passwd --stdin $uName &> /dev/null
echo "$uName is created !"
}
done
2. While loop (condition is true)
while 条件
do
语句1
语句2
done
Infinite loop format 1:
while true
do
语句
done
Infinite loop format 2:
while :
do
语句
done
3. until loop (condition is false)
The until loop executes a series of commands until the condition is true and stops.
The until loop and the while loop are handled in the opposite way.
Generally the while loop is better than the until loop, but in some cases—and only in rare cases, the until loop is more useful
until 条件
do
语句1
语句2
done
4. if
if 条件
then
语句
elif 条件
then
语句
else
语句
fi
(If the else branch has no statement to execute, don't write this else)
Exercise 1:
check_file.sh
detects whether the file exists and determines the file type
#!/bin/bash
while true
do
read -p "Please input filename:" fileName
if [ "$fileName" == "exit" ]
then
exit
fi
if [ -e "$fileName" ]
then
if [ -f "$fileName" ]
then
echo "$fileName is 普通文件 ! "
elif [ -d "$fileName" ]
then
echo "$fileName is 目录 ! "
elif [ -S "$fileName" ]
then
echo "$fileName is 套接字 ! "
elif [ -L "$fileName" ]
then
echo "$fileName is 软链接 ! "
elif [ -b "$fileName" ]
then
echo "$fileName is 块设备 ! "
elif [ -c "$fileName" ]
then
echo "$fileName is 字符设备 ! "
fi
else
echo "$fileName is not exist !"
fi
done
5. case
The case statement is a multiple choice statement. You can use the case statement to match a value and a pattern. If the match is successful, execute the matched command
case 值 in
模式1)
语句
;;
模式2)
语句
;;
*)
语句
;;
esac
(" *) "indicates other circumstances)
Exercise:
Add disk or memory or upload after system_watch.sh, execute as follows:
- disk monitor disk usage
- memory monitor memory usage
- upload monitor start load
- Display per second
#!/bin/bash
while true
do
[ "$1" = "exit" ] && {
exit
}
case $1 in
disk|DISK)
watch -n 1 "df -h "
exit
;;
memory|MEMORY)
watch -n 1 "free -m"
exit
;;
upload|UPLOAD)
watch -n 1 "uptime"
exit
;;
esac
done
6. Expect automatic conversation
dnf install expect -y: Install expect
Question script: ask.sh (give execution permission)
#!/bin/bash
read -p "What's your name: " NAME
read -p "How old are you: " AGE
read -p "which class? " CLASS
read -p "How do you feel? " FEEL
echo $NAME is $AGE\'s old study $CLASS fell $FEEL
Answer script 1: answer.exp
#!/usr/bin/expect
spawn /mnt/ask.sh
expect "name"
send "tom\r"
expect "old"
send "18\r"
expect "class"
send "linux\r"
expect "feel"
send "happy\r"
expect eof
Answer script 2: answer.exp
#!/usr/bin/expect
set timeout 2
spawn /mnt/ask.sh
expect {
"name" {
send "tom\r"; exp_continue }
"old" {
send "18\r"; exp_continue }
"class" {
send "linux\r" ; exp_continue }
"feel" {
send "happy\r" }
}
expect eof
Answer script 3: answer.exp
#!/usr/bin/expect
set NAME [ lindex $argv 0 ]
set AGE [ lindex $argv 1 ]
set CLASS [ lindex $argv 2 ]
set FEEL [ lindex $argv 3 ]
set timeout 2
spawn /mnt/ask.sh
expect {
"name" {
send "$NAME\r" ; exp_continue }
"old" {
send "$AGE\r" ; exp_continue }
"class" {
send "$CLASS\r" ; exp_continue }
"feel" {
send "$FEEL\r" }
}
expect eof
Answer script 4: answer.sh
#!/bin/bash
echo hello zy !
/usr/bin/expect <<EOF
set timeout 2
spawn /mnt/ask.sh
expect {
"name" { send "$1\r" ; exp_continue }
"old" { send "$2\r" ; exp_continue }
"class" { send "$3\r" ; exp_continue }
"feel" { send "$4\r" }
}
expect eof
EOF
Exercise:
host_list.sh
detects whether the 172.25.254.1-172.25.254.10 network is normally turned on, if the network is normal, please generate a resolution list host_list
#!/bin/bash
EXPECT()
{
/usr/bin/expect <<EOF
set timeout 2
spawn ssh root@$1 hostname
expect {
"yes/no?" { send "yes\r" ;
expect "password:" ;
send "$2\r";
exp_continue; }
"password:" { send "$2\r" }
}
expect eof
EOF
}
for i in {
1..10}
do
ping -c1 -w1 172.25.254.$i &> /dev/null
if [ "$?" = "0" ]
then
host_name=`EXPECT 172.25.254.$i westos | tail -n 1`
grep $host_name /mnt/host_list &> /dev/null || {
echo "172.25.254.$i $host_name" >> /mnt/host_list
}
fi
done
sed 's/^M//g' -i /mnt/host_list
#^M为<ctrl>+<V>+<M>
7. Break out of the loop (break and continue and exit)
break: Allow to jump out of all loops (terminate all loops after execution)
continue: It will not jump out of all loops, just out of the current loop
exit:drop out