Xml and More: Expect Scripts: How to Automate Your Tasks

Task to be Automated

Below shows an interactive session that psm — an Oracle Application Container Cloud Service command line tool—prompted a user for needed authentication and authorization information before he/she can sign in to an Oracle Cloud service and work on a specific identity domain.


$ psm setup

Username: weblogic1

Password:

Retype Password:

Identity domain: myIdDomain

Region [us]: http://anycloudserver.example.com:7103

Output format [json]:

In this article, we will demonstrate how to utilize Expect to automate the above task , but not focus on the correctness of the information needed by psm.

Expect

Expect is an extension to the Tcl scripting language that "talks" to other interactive programs according to a script.^[1] Following the script, Expect knows what can be expected from a program and what the correct response should be.

It can be used to automate control of interactive applications such as telnet, ftp, passwd, fsck, rlogin, tip, ssh, and others including psm . Expect uses pseudo terminals (Unix) or emulates a console (Windows), starts the target program, and then communicates with it, just as a human would, via the terminal or console interface. Finally, Tk, another Tcl extension, can be used to provide a GUI.

Expect Script

To automate the said task, we need to write an Expect script (i.e., psmSetup.exp) as shown below:

psmSetup.exp




#!/usr/bin/expect -f
#exp_internal 1
set argDomain [lindex $argv 0]
spawn psm setup
expect "Username: "
send "weblogic\r"
expect "Password: "
send "welcome1\r"
expect "Retype Password: "
send "welcome1\r"
expect "Identity domain: "
send "$argDomain\r"
expect "Region \\\[us\\\]: "
send "http://anycloudserver.example.com:7103\r"
expect "Output format \\\[json\\\]: "
send "\r"
expect "\r"
spawn psm accs apps
expect "\r"

Expect scripts can have any file name suffix you like, though they generally have an .exp extension. Read [5] for more details.

How to Debug Expect Scripts?

Writing an Expect script the first time, it is easy to be completely lost and not getting the result you expect. In this case, un-comment the following line in psmSetup.exp:

#exp_internal 1

Setting "exp_internal 1" at the beginning of an Expect script is similar to -d flag (When using Expectk, this option is specified as -diag.), which enables some diagnostic output. This primarily reports internal activity of commands such as expect and interact. In addition, the strace command is useful for tracing statements, and the trace command is useful for tracing variable assignments.

How to Pass Variables from Shell Script to Expect Script?

Say, if you write a Korn shell script as below:

#!/bin/ksh
...

./psmSetup.exp $domain

and would like to pass $domain from shell script to psmSetup.exp script, you can add the following line to the Expect script:

set argDomain [lindex $argv 0]

To reference the Expect variable (i.e, argDomain), you use prefix "$" as below:

expect "Identity domain: "
send "$argDomain\r"

In the above psm dialog, it depicts the interaction between a sender (i.e., end user) and a receiver (i.e. psm) as:

"Identity domain: " is the prompt you "expect" from the psm; therefore, you enter that expected response (i.e., "$argDomain\r") by using "send".

Read [7] for more explanation.

How to Escape Special Characters?

In the below dialog,

Region [us]: http://anycloudserver.example.com:7103

psm will prompt the user for a response:

Region [us]:

which includes some special characters "[" and "]". To escape special characters in Expect, you can use backslash. However, to protect backslash from being substituted, you actually need to use "\\\" in front of both "[" and "]":^[9-12]

expect "Region \\\[us\\\]: "
send "http://anycloudserver.example.com:7103\r"

Sunday, April 3, 2016

Expect Scripts: How to Automate Your Tasks

Expect

Expect Script

How to Debug Expect Scripts?

How to Pass Variables from Shell Script to Expect Script?

How to Escape Special Characters?

References

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