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Expect

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Man page:expect

Usage ​

Expect is a program that "talks" to other interactive programs according to a script. It is an extension of Tcl.

Some common commands are:

CommandDescription
spawnStarts a script or a program.
expectWaits for program output.
sendSends a reply to your program.
interactAllows you to interact with your program.
setDefines a variable. May also read arguments.

Variables:

VariableDescription
envAn array containing environment variables. Ex: $env(PATH)

Use "" in strings for variables and special characters interpolation.

Use {} in strings for non-interpolating quotes.

Tricks ​

Add the code at the beginning of the expect script to have terminal resize support:

shell
trap {
  set rows [stty rows]
  set cols [stty columns]
  stty rows $rows columns $cols < $spawn_out(slave,name)
} WINCH

Examples ​

SSH into a step_server:

shell
spawn ssh step_server

set argument [lindex $argv 0];

expect "password:"
send -- "$argument\r"

send -- "PS1='$env(BASH_PROMPT)'\r"

interact

Jump some servers and set prompt:

shell
set user "myuser"
set pass "mypass"
set serv "myserv"

spawn ssh step_server
expect {
  "yes/no" { send "yes\r"; exp_continue }
  "password:" { send "secret\r" }
}
expect {
  "step_server ~]\\\$" { send "ssh $user@$serv\r"; exp_continue }
  "password:" { send "$pass\r" }
}

send -- {PS1="\n[\D{%Y-%m-%d %H:%M:%S] \u@\h:\w\n\$ "}
send -- "\r"

interact