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.