A Telnet Client Using Expect

The following expect script achieves a simple telnet client: login -> send command -> exit. The point is the form of prompt in regular expression. You have to add 3 backslash before "[", "]" and "$", and add "-re" option after expect command in "expect $prompt".

#!/usr/bin/expect
set prompt "\[hadoop@49server\s.*\]\\$\s"
spawn telnet 10.0.2.49
expect "login:"
send "hadoop\r"
expect "Password:"
send "h\r"
expect -re $prompt
send "df -h\r"
expect -re $prompt
send "ls -l\r"
expect -re $prompt
send "exit\r"
expect eof

The following script achieves auto-login and auto-logout. Save it as autoTelnet.exp:

#!/usr/bin/expect
set ip [lindex $argv 0]
set username [lindex $argv 1]
set password [lindex $argv 2]
spawn telnet $ip
expect "login:"
send "$username\r"
expect "Password:"
send "$password\r"
interact +++ return
send "exit\r"
expect eof

then run it:

$ ./autoTelnet.exp 10.0.2.49 hadoop h

After auto-login, you can send any commands as if you communicates with host directly. When you want to quit, type "+++" and then the script exits from interact mode and runs logout routine.