Expect.md

Expect Scripting Language

• Expect is a tool that help in automating scripts.

• Expect scripting language works by expecting input, then the Expect script will send the response without any user interaction.

$ apt-get install expect

Expect commands

Command	Description
spawn	Starts a script or a program
expect	Waits for program output
send	Sends a reply to your program
interact	Allows to interact with the program

# disable timeout
set timeout -1

• Use spawn to run any program

• To build an expect script automatically, use autoexpect command.

autoexpect ./questions.sh

• Use set command to define variables in expect scripts

set NAME Aamir
set COUNT 4

• To use command line arguments in expect scripts

set MYVAR [lindex $argv 0]

• Use conditional tests using braces

expect {

    "something" { send -- "send this\r" }

    "*another" { send -- "send another\r" }

}

if else conditions

#!/usr/bin/expect -f

set NUM 1

if { $NUM < 5 } {

    puts "\Smaller than 5\n"

} elseif { $NUM > 5 } {

    puts "\Bigger than 5\n"

} else {

    puts "\Equals 5\n"

}

• NOTE: Opening brace must be on same line.

while loops

#!/usr/bin/expect -f

set NUM 0

while { $NUM <= 5 } {

    puts "\nNumber is $NUM"

    set NUM [ expr $NUM + 1 ]

}

puts ""

for loop

#!/usr/bin/expect -f

for {set NUM 0} {$NUM <= 5} {incr NUM} {

    puts "\nNUM = $NUM"

}

puts ""

User-defined Functions

You can define a function using proc like this:

proc myfunc { TOTAL } {
    set TOTAL [expr $TOTAL + 1]
    return "$TOTAL"
}

set NUM 0

while {$NUM <= 5} {
    puts "\nNumber $NUM"
    set NUM [myfunc $NUM]
}
puts ""

Interact Command

• The interact command reverts the control to the keyboard.