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Expect Automate interactive programs

Version 5.45.3 · source

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Start here

spawn <cmd> [args]
Start a program
expect "<pattern>"
Wait for its output
send "<text>\r"
Type into it
interact
Hand over the keyboard
set timeout <sec>
Change the 10 s wait
expect eof
Wait for exit
expect -f <script>
Run a script file
autoexpect <cmd>
Record a session

Concepts

  1. spawn start program on a pty
  2. expect match pattern
  3. send type the reply
  4. interact / eof hand over or finish

Running

expect <script> [args]
Run a script file
expect -d <script>
Run with diagnostic output
Shows what is matched against which pattern; the first tool when a script hangs.
#!/usr/bin/env expect
Shebang for executable scripts
autoexpect [-f <out>] <cmd>
Record a session as a script
unbuffer <cmd>
Run a command with a pty attached

Spawn and send

spawn <cmd> [args]
Start a program on a pty
spawn -noecho <cmd>
Spawn without echoing the command line
send "<text>\r"
Type text and press Enter
send -- "<text>"
Send text that starts with a dash
send -s "<text>"
Send slowly (uses send_slow)
send -i $<id> "<text>"
Send to a specific spawn id
send_user "<text>"
Print to your terminal
set <id> $spawn_id
Save the current spawn id
wait
Reap the process, get its exit status
exit [<status>]
Exit the script
sleep <sec>
Pause (decimals allowed)

Expect patterns

expect "<glob>"
Wait for output matching a glob
expect -re "<regexp>"
Wait for a regexp match
expect -ex "<text>"
Wait for exact text, no wildcards
expect eof
Wait for the process to end
expect timeout { <cmds> }
Run commands when the wait times out
expect { "a" {<cmds>} "b" {<cmds>} }
Several patterns, first match wins
exp_continue
Keep matching after an action
Resets the timeout; add -continue_timer to keep the running clock.
expect -timeout <sec> "<pat>"
Timeout for this one wait
expect_before { <pat> {<cmds>} }
Patterns tried before every expect

Variables

set timeout <sec>
Default wait; -1 waits forever
$expect_out(buffer)
Output consumed by the last match
$expect_out(0,string)
Text of the whole match
$expect_out(1,string)
First -re capture group
$spawn_id
Id of the current process
$argv / $argc / $argv0
Script arguments, count, name
lindex $argv <n>
Get argument number n
$env(<NAME>)
Read an environment variable

Interact

interact
Give the keyboard to the process
interact { "<key>" { <cmds> } }
Run commands when you type a string
interact timeout <sec> { <cmds> }
Act after idle seconds
return
Leave interact, continue the script
log_user 0
Hide the process output from you
stty -echo
Turn off echo (for passwords)
expect_user -re "(.*)\n"
Read a line typed by the user

Logging, debug and signals

exp_internal 1
Print match diagnostics to stderr
log_file <file>
Record the session to a file

Tcl essentials

set <var> <value>
Assign a variable
foreach h $hosts { ... }
Loop over a list
proc <name> {<args>} { ... }
Define a procedure
regexp {<re>} $str -> a b
Match, capture into variables
[exec <cmd>]
Run a command and capture output

Recipes

Login over ssh
set timeout 20spawn ssh <user>@<host>expect { "yes/no" {  send "yes\r"  exp_continue } "assword:" {  send "$env(PW)\r" }}interact
Run one command and capture output
spawn ssh <host> uptimeexpect -re {average: ([0-9.]+)}puts $expect_out(1,string)expect eof
Exit code of the spawned program
spawn <cmd>expect eoflassign [wait] pid id os rcexit $rc