最後更新: 2023-09-28

介紹

expect offers a way to control interactive applications which require user input to continue.

Expect uses Tcl (Tool Command Language)

Install

dnf install expect -y

expect -v

expect version 5.45.4    # R8

Usage

expect [options] [commands/command file]

options

-f    Specifies a file to read from.
-c    Specifies the command to execute before the script.

Run by script

#!/usr/bin/expect -f

主要 Syntax

• spawn      Creates a new process.
• send         Sends a reply to the program.
• expect      Waits for output.
• interact     Enables interacting with the program.

Example

[1] expect

Syntax:

expect patterns|keyword action

Pattern:

1. Default: string matching is glob-style patterns (*, ?)
2. "-ex" flag causes the pattern to be matched as an "exact" string.
3. "-re" flag forces the string to be interpreted as a regexp-style pattern.

keyword: 

• eof            # The default eof action is "return" => 返回 interact
• timeout     # Default timeout is 10 seconds
• default      # corresponding body is executed upon either timeout or end-of-file

input.sh

#!/bin/bash

read -p "Please input a number: " ANSWER
echo "You input $ANSWER"

ans.sh

#!/usr/bin/expect -f

expect "Please input"
send "1\r"

# 必須加, 否則見會見唔到 "You input $ANSWER"
expect eof

Notes

Script 多數以 "expect eof" 或 "interact" 結尾.

"expect eof" 的功能: 等待 EOF condition

當沒有 "expect eof" , 那 script 就會在 send 之立即中止

[2] timeout & set 的應用

Default timeout is 10 seconds

#!/usr/bin/expect -f

set timeout 3
set pw MYPW

spawn ssh -p 22 USER@SERVER_IP

expect {
    "yes/no" { send "yes\r";exp_continue }
    "password:" { send "$pw\r" }
}

interact

[3] User input

set user [lindex $argv 0]

set password [lindex $argv 1]

expect auto_login.exp user_name some_password

[4] msg to user

puts vs send_user

if you're using log_file, send_user will make it into the logfile, whereas statements sent with puts do not.
puts automatically appends a newline and send_user does not.

send_error[-flags] string

[5] log

send_log [--] string
log_file[args] [[-a] file]

will record a transcript of the session in the file.
By default, the log_file command appends to old files rather than truncating them
To truncate files, use the -noappend flag.

[6] Other

sleep seconds