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Basic Overview of Expect

Expect is generic, so it can be run as a user-level command, regardless of any programs or tasks. Expect can actually talk to multiple programs at the same time. Expect is very useful for programs that require programs to interact with users. Expect can also return control to the user if necessary without having to stop the controlled program. Similarly, the user can return control to the script at any time.

Common option

-c: the command prefix before any command to be executed in the script. You should surround the command in quotation marks to prevent it from being destroyed by shell. This option can be used multiple times. Multiple commands can be executed sequentially with a-c, separated by a semicolon (use the-command option if Expectk is used).

-d: enable some diagnostic output, mainly reporting the internal activity of commands such as expect and interact. This option has the same effect as exp_internal 1. And print the version of Expect. For example, the strace command is used to trace statements, and the trace command is used to trace variable assignments (use the-diag option if Expectk is used).

-D: enable the interactive debugger. Followed by an integer value, if the value is non-zero, Ctrl+C is pressed, a breakpoint is hit, or other appropriate debugger commands appear in the script, the debugger will retain control until the next Tcl procedure (use the-Debug option if Expectk is used).

-f: marks in front of the file from which you want to read the command. -f itself is optional. On the command line, if-f is not provided, the command ends after the command in the file is executed, the subsequent expect option is ignored, and if-f is provided, the subsequent expect option is not ignored. When expect is implicitly called in a script, if-f is not provided, the expect option is treated as a normal positional parameter. If provided, an attempt is made to identify the expect option (or the-file option if Expectk is used).

-b: forces the file to be read and executed line by line. By default, command files are read into memory and all executed (if Expectk is used, the-buffer option is used). If the file name provided to-f and-b is "-", it is read from standard input.

-i:expect prompts for commands interactively instead of reading them from a file. The prompt is terminated by the exit command or EOF. If you do not use a command file or

-c,-I is used by default (the-interactive option is used if Expectk is used).

-: used to separate the end of the option. It is useful for passing parameters of similar options that you do not want to interpret by expect. The following parameters will not be attempted to resolve to the expect option. -- can also be used with #! Use it together. All options that follow the start of the first non-expect option are resolved as normal parameters.

-N: prevents expect from automatically fetching the $exp_library/expect.rc file, if the file exists (use the-NORC option if Expectk is used).

-n: after $exp_library/expect.rc, disable expect from automatically getting the ~ / .encrypt.rc file, if the file exists (use the-norc option if Expectk is used). If the environment variable DOTDIR is defined, the .account.rc file is obtained from its specified location.

-v: print the expect version number (use the-version option if Expectk is used).

Args: the optional args is constructed into a list and saved in the variable argv. The variable argc is initialized to the length of the argv. Argv0 is defined as the name of the script.

Example

Expect direct and embedded

1. Use expect to realize the interaction-free ssh service by writing directly.

#! / usr/bin/expect set timeout 20 / / timeout / / parameters are passed in set hostname [lindex $argv 0] set password [lindex $argv 1] / / pursuit command spawn ssh root@$hostname// pursues the information and executes interaction-free expect {"(yes/no)" {send "yes\ r" Exp_continue} "* password" {send "$password\ r"}} / / transfer execution permissions to the console output interact [root@localhost ~] # chmod + x expect.sh / / add execution permissions to the script [root@localhost ~] #. / expect.sh 192.168.100.137 qweqwe / / execute the script and enter the ip and login password of the ssh login user / / the result spawn ssh root@ of the script execution 192.168.100.137The authenticity of host '192.168.100.137 (192.168.100.137)' can't be established.ECDSA key fingerprint is SHA256:nbnd6568zTp0Fgdo2gavS4YXLySyTvs7+JT/b7L/syU.ECDSA key fingerprint is MD5:0d:02:8f:c9:28:e3:41:30:f7:fd:94:94:2d:ff:ff:dd.Are you sure you want to continue connecting (yes/no)? YesWarning: Permanently added '192.168.100.137' (ECDSA) to the list of known hosts.root@192.168.100.137's password: Last login: Fri Oct 11 17:02:57 2019 from 192.168.100.1

Enter "ipconfig" to check whether the ip address of the currently logged in user is 192.168.100.137

If you want to wait, enter the "exit" command to wait for the current user.

[root@localhost ~] # exit logout

2. Use expect embedding and writing to realize ssh service interaction-free.

#! / bin/bashhostname=$1password=$2/usr/bin/expect

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