Leo at 06:02, 13 July 2021

2021-07-13T06:02:31Z

← Older revision		Revision as of 06:02, 13 July 2021
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	Places where I've used expect include automating fdisk, installers (like the Nvidia Linux driver), and telnet.		Places where I've used expect include automating fdisk, installers (like the Nvidia Linux driver), and telnet.

	== Introduction ==		==Introduction==

	=== Installation ===		===Installation===
	Install expect on your system by running:		Install expect on your system by running:

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	<code>yum install expect</code>		<code>yum install expect</code>

	=== Quick start ===		===Quick start===
	There are two ways to write expect scripts:		There are two ways to write expect scripts:

	# Write the expect script in a file with the <code>#!/usr/bin/expect</code> hash bang header and execute the script like any other shell script		#Write the expect script in a file with the <code>#!/usr/bin/expect</code> hash bang header and execute the script like any other shell script
	# Pass the expect script during execution, like most short <code>awk</code> scripts.		#Pass the expect script during execution, like most short <code>awk</code> scripts.

	An example expect script would look like this:		An example expect script would look like this:
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	\|<code>interact</code>		\|<code>interact</code>
	\|Pass the program input to the user		\|Pass the program input to the user
			\|-
			\|<code>set</code>
			\|Sets a variable.
			Eg. Username set to the first argument: <code>set Username [lindex $argv 0]</code>
	\|}		\|}

			=== Conditions ===
			Conditional reply based on an expected string:
			{{Highlight
			\| code = expect {
			"*movie?" { send -- "The Godfather\r" }
			"*song?" { send -- "Sandstorm\r" }
			}
			\| lang = expect
			}}
			Conditional reply based on some variable:
			{{Highlight
			\| code = if ( $Username == "leo" ) {
			puts "leo\r"
			} else {
			puts "other\r"
			}
			\| lang = terminal
			}}
	<br />		<br />

	== Tasks ==		==Tasks==

	=== Use expect to telnet to a device and reboot it ===		===Use expect to telnet to a device and reboot it===
	I have a Wyze Cam which I sometimes would want to reboot if something stops working with it. To do so, use the following expect script (which I inlined as part of a bash shell script):		I have a Wyze Cam which I sometimes would want to reboot if something stops working with it. To do so, use the following expect script (which I inlined as part of a bash shell script):
	{{Highlight		{{Highlight
Line 80:		Line 103:
	}}		}}
	Note that the <code>expect *#</code> after the reboot command is required. Without this final expect, expect will exit before the reboot gets triggered.		Note that the <code>expect *#</code> after the reboot command is required. Without this final expect, expect will exit before the reboot gets triggered.

			<br />

			== See Also ==

			* https://likegeeks.com/expect-command/

Leo: Initial Content

2021-07-13T05:56:30Z

Initial Content

New page

Expect is a utility that makes it easy to automate commands that require user input via STDIN.

Places where I've used expect include automating fdisk, installers (like the Nvidia Linux driver), and telnet.

== Introduction ==

=== Installation ===
Install expect on your system by running:

<code>apt-get install expect</code>

<code>yum install expect</code>

=== Quick start ===
There are two ways to write expect scripts:

# Write the expect script in a file with the <code>#!/usr/bin/expect</code> hash bang header and execute the script like any other shell script
# Pass the expect script during execution, like most short <code>awk</code> scripts.

An example expect script would look like this:
{{Highlight
| code = #!/usr/bin/expect -f

set timeout -1

spawn passwd

expect "New password:\r"
send "new-password123\r"

expect "Retype new password:\r"
send "new-password123\r"

expect eof
| lang = expect
}}
Looking at this example script, it should be evident what the script does. Simply put, an expect script starts a program (with <code>spawn</code>), then expects a certain string (<code>expect</code>), and then sends a reply based on this condition (<code>send</code>).

The commands that expect supports are listed below.
{| class="wikitable"
!Command
!Description
|-
|<code>spawn</code>
|Starts a program or script
|-
|<code>expect</code>
|Wait for a specific program output
|-
|<code>send</code>
|Writes a reply to the program
|-
|<code>interact</code>
|Pass the program input to the user
|}
<br />

== Tasks ==

=== Use expect to telnet to a device and reboot it ===
I have a Wyze Cam which I sometimes would want to reboot if something stops working with it. To do so, use the following expect script (which I inlined as part of a bash shell script):
{{Highlight
| code = #!/bin/bash

if something-went-wrong ; then
expect -c "
set timeout 10
spawn telnet ${CAM_IP}
expect \"login:\"
send \"root\r\"
expect \"Password:\"
send \"${CAM_PASSWORD}\r\"
expect \"*# \"
send \"reboot\r\"
expect \"*# \"
exit"

fi
| lang = terminal
}}
Note that the <code>expect *#</code> after the reboot command is required. Without this final expect, expect will exit before the reboot gets triggered.

Expect - Revision history

Leo at 06:02, 13 July 2021

Leo: Initial Content