如何在Expect脚本中使用变量作为期望值（expect -re regex）

Question

I have an expect script where I do not always know the output, nor do I want to hardcode the expected output returned from a given command, instead I pass in a part of the expected output as a command line variable. I then want to use the expected output as part of a regex to validate against.

I've looked at a few examples and can only see cli vars being used with the send command but not with the expect -re command.

#!/usr/bin/expect

set output [lindex $argv 0]
set host [lindex $argv 1]

set regex "{(?n)^${output}.*}"
puts $regex

set timeout -1

spawn ssh root@$host
expect -re {(?n)^Password.*}

send "myPassword\n"
expect -re $regex

expect eof

OUTPUT

Password: couldn't compile regular expression pattern: quantifier operand invalid
    while executing
"expect -re $regex"

EXPECTED Regex should be handled as a the value set in the output cli variable.

Note well: when values are hardcoded the script works as expected

Answer 1

Braces in a regular expression are quantifier syntax. For example, to find 3 "a", you can use a{3}

Your assignment of the $regex variable contains literal braces

set regex "{(?n)^${output}.*}"

expect is an extension of the Tcl language: in Tcl, you use double quotes to enclose a "word" allowing variable and command substitution; you use braces to enclose a word with no substititions allowed (like single quotes in the shell).

Simply remove the braces from the $regex value.