Shell programming-Here Document free interaction and Expect interaction

Here Document Free Interaction

• Overview
  • Use I/O redirection to provide the command list to the interactive program
  • An alternative to standard input
  • Grammatical format

命令 <<标记    #一般使用EOF
...
内容          #标记之间是传入内容
...
标记

Precautions for Use of Here Document

• The mark can use any legal character (usually EOF)
• The ending mark must be written in the top grid without any characters in front
• There can be no characters (including spaces) after the ending tag
• The spaces before and after the opening tag will be omitted

Here Document regular usage

• Interaction-free way to realize the statistics of the number of rows EOF, put the content to wc -lbe counted between the tags , and directly pass the content to the statistics

wc -l <<EOF
>Line1
>Line2
>EOF

• Receiving a command input via read and print the input value is the two EOFportions between the marks, as a variable ivalue

read i <<EOF
>hello         #hello后面有自带的换行符有回车的功能所以$i只会获取第一行变量
>EOF
echo $i

• Set a password for the user through passwd

passwd zhangsan <<EOF
>123456                    #这两行是输入的密码和确认密码
>123456
>EOF

• Support variable replacement
  When writing the file, the variable will be replaced with the actual value, and then combined with the cat command to complete the writing

#!/bin/bash
file="EOF.txt"
i="substitution"
cat > $file <<EOF
Support variable $i
EOF

cat EOF.txt

• Copy the whole to the variable, and then print the variable value through the echo command

#!/bin/bash
var="Great! I am going to school!"
myvar=$(cat <<EOF
This is Line 1
Todey is Monday
$var
EOF
)
echo $myvar

• Turn off the variable replacement function, and output the characters as they are, without any modification or replacement

#!/bin/bash
var="Great! I am going to school!"
myvar=$(cat <<'EOF'            #对标记加单引号或双引号，即可关闭变量替换
This is Line 1
Todey is Monday
$var
EOF
)
echo $myvar

• Remove the TAB character before each line

#!/bin/bash
var="Great! I am going to school!"
myvar=$(cat <<-EOF
        This is Line 1      #在标记前加"-"，即可压制各种行首TAB
                Todey is Monday
                        $var
EOF
)
echo "$myvar"

• Multi-line comments
  Bash's default comment is #that this comment method only supports single-line comments: The introduction of Here Document solves the problem of multi-line comments, which
  :represents an empty command that does nothing. The content of the middle mark area will not be executed and will be ignored by bash, so the effect of batch comments can be achieved

#!/bin/bash
var="Great! I am going to school!"
: <<-EOF
                        This is Line 1 .
                Today is Monday .
        $var
EOF
echo "abcd"

Expect basic commands

A tool built on the basis of the tcl language, often used for automated control and testing, to solve interactive problems in shell scripts
rpm -q expect
rpm -q tcl
yum install -y expect

Script interpreter

• The file is first introduced in the expect script to indicate which shell is used
  #!/usr/bin/expect

spawn

• Spawn is usually followed by a Linux execution command, which means opening a session, starting a process, and tracking subsequent interaction information.
  Example: spawn passwd root

expect

• Determine whether the last output result contains the specified string, if there is, return immediately, otherwise return after waiting for the timeout period; Can only capture the output of the process started by spawn;
  Used to receive the output after the command is executed, and then meet the expectations String matching

send

• Send a character string to the process to simulate the user's input; this command cannot automatically enter and line feed . Generally, you must add \r (carriage return) or \n. Example:

方式一：
expect "密码" {send "abc123\r"}  #同一行send部分要有{}

方式二：
expect "密码" 
send "abc123\r"       #换行send部分不需要有{}

方式三：
expect支持多个分支
expect     #只要匹配了其中一个情况，执行相应的send语句后退出该expect语句
{
"密码1" {send "abc123\r"}
"密码2" {send "123456\r"}
"密码3" {send "123123\r"}
}

Two types of terminator

expect eof

• Indicates the end of the interaction, waiting for the execution to end, and returning to the original user, corresponding to spawn. For
  example, when switching to the root user, the expect script waits for 10s by default. When the command is executed, it will automatically switch back to the original user after it stays for 10s by default.

interact

• After the execution is completed, the interactive state is maintained, and the control is transferred to the console. It will stay at the target terminal instead of returning to the original terminal. At this time, you can manually operate it. The command after interact does not work, such as adding exit after interact. It will not exit the root user. If there is no interaction, it will log out after the login is completed, instead of staying on the remote terminal
• If you use interact, you will stay in the terminal instead of returning to the original terminal. For example, when you switch to the root user, you will always be in the root user state; for example, when you ssh to another server, you will always be in the target server terminal instead of switching back to the original server.

Note: expect eofwith interactonly a second election.

set timeout set timeout

• The default timeout period of expect is 10 seconds. The session timeout period can be set through the set command. If the timeout period is not limited, it should be set to -1

例：set timeout 30

exp_continue continue to match

• exp_continue is appended to a certain expect judgment item, so that after the item is matched, it can continue to match
  other items in the expect judgment sentence. exp_continue is similar to the continue statement in the control statement. Indicates that expect is allowed to continue to execute instructions downward
• For example: The following example will determine whether there is yes/no or *assword in the interactive output. If it matches yes/no, output yes
  and execute the judgment again; if it matches *password, output abc123 and end the expect statement

expect {
    "(yes/no)" {send "yes\r"; exp_continue;}
    "*password" {set timeout 300; send "abc123\r";}
}

Note: When using exp_continue, if you follow a command such as passwd that ends the process after entering the password, do not add expect eof outside of expect{}
because after the spawn process ends, it will send eof to expect by default, which will cause the subsequent expect eof to be executed. Report an error

send_user

• send_user means echo command, equivalent to echo

Receive parameter set

• The expect script can accept parameters passed from the bash command line and get it using [lindex $argv
  n]. Among them, n starts from 0 and represents the first, second, third...parameters respectively.

Example:
set hostname [lindex $argv 0] 相当于 hostname=$1
set password [lindex $argv 1] 相当于 password=$2

expect to execute directly

Need to use the expect command to execute the script
su to switch users
#!/usr/bin/expect
#设置超时时间
set timeout 5

• Parameters are passed in to
  set username [lindex $argv 0]get the first positional parameter to
  set password [lindex $argv 1]get the second positional parameter
• Start tracking command
  spawn su $usernamecall variable value
• No interactive execution. After capturing information and matching
  expect "密码"su, there will be a string of passwords, and the expected string will be captured
  send "$password\r"because there is no carriage return function, so you need to add it \ror \n
expect "*]#"a command prompt will appear after logging in, so fill in the quotation marks *]#
  send user "ok"match Success is equivalent to echo an OK display
• Give control to the console if
  interact
#expect eofyou want to exit, use expect eof to exit through the set timer

Embedded execution mode

Integrate the expect process into the Shell to facilitate execution and processing

• Create user and set password
  #!/bin/bash
user=$1
password=$2
• Non-interactive commands are placed outside expect
  useradd $user
• Start to execute
  /usr/bin/expect <<-EOFexpect without exchange. The start flag starts
  spawn passwd $usera process tracking passwd command. Expect can only capture the process information.
  expect "新的*"
send "$ {password}\r" .
expect "重新*"
send "$ {password} \r"
expect eof
EOF

Realize ssh automatic login

• 
  #! /usr/bin/ expect
set timeout 5
set hostname [l index $argv 0 ]
set password [l index $argv 1]
spawn ssh $hostname
expect { There are many possibilities for
  "Connection refused" exitconnection failure. The other party's ssh service may be closed (the content prompted by different versions may be different, this is centos7), the
  "Name or service not known" exitserver cannot be found, and the IP address may be entered incorrectly (the content of the prompt may be different for different versions, this is centos7)
  " (yes/no)" {send "yes\r" ;exp_ continue}If it matches the result of yes/no, it will choose yes to continue the subsequent operation. The
  "password:" {send "$password\r"}rest will only match this result, then execute this content directly. Calling
  interactthe command after $password interact does not work.
  exit

Create disk partitions without interaction

• Prepare a new disk
• Script content
  #!/bin/bash
read -p "输入需要创建的磁盘分区" a
/usr/bin/expect <<-EOF
spawn fdisk $a
expect "命令" {send "n\r"}
expect "Select" {send "\r"}
expect "分区" {send "\r"}
expect "起始" {send "\r"}
expect "Last" {send "\r"}
expect "命令(输入 m 获取帮助)：" {send "w\r"}
expect eof
EOF
partprobe
mkfs.xfs $a -f &> /dev/null
if [ $? -eq 0 ]
then
echo -e "\033[31m 磁盘格式化完成 \033[0m"
mkdir $a.1
mount $a $a.1
df -h
else
echo "格式化失败，脚本有问题"
fi
• Install expect
• Execute script
  shorchmod +x提权再./