How to escape square brackets in expect?

Question

I am not able to escape square braces in the expect script, the example as below,

I have a question.sh script as below,

#!/bin/bash
echo "Would you like to specify inputs and execute the script? [Y/n]"
read $REPLY

echo "Deleted Item with ID: 50 and do cleanup? [Y/n]"
read $REPLY

echo "Deleted Item with ID: 51 and do cleanup? [Y/n]"
read $REPLY

echo "Deleted Item with ID: 52 and do cleanup? [Y/n]"
read $REPLY

For the above question.sh I have the below answer.exp, and execute the same with 'expect answer.exp 51' command,

#!/usr/bin/expect -f

set timeout -1

spawn ./question.sh

set item "Deleted Item with ID: "
append item [lindex $argv 0]
append item " and do cleanup? \[Y/n\]"

expect "Would you like to specify inputs and execute the script? \[Y/n\]"
send -- "Y\r"

expect {

      $item {
            send "Y\r"
            exp_continue
      }
      " and do cleanup? \[Y/n\]" {
            send "n\r"
            exp_continue
      }
}

When ever I have the square braces involved the expect is not matching and does not send the answer (Y/N) back.

The same when I remove the square braces from the question and the answer scripts expect works fine, the changed question and answer scripts as below.

question.sh:

 #!/bin/bash
echo "Would you like to specify inputs and execute the script? Y/n"
read $REPLY

echo "Deleted Item with ID: 50 and do cleanup? Y/n"
read $REPLY

echo "Deleted Item with ID: 51 and do cleanup? Y/n"
read $REPLY

echo "Deleted Item with ID: 52 and do cleanup? Y/n"
read $REPLY

answer.exp:

#!/usr/bin/expect -f

set timeout -1

spawn ./question.sh

set item "Deleted Item with ID: "
append item [lindex $argv 0]
append item " and do cleanup? Y/n"

expect "Would you like to specify inputs and execute the script? Y/n"
send -- "Y\r"

expect {

      $item {
            send "Y\r"
            exp_continue
      }
      " and do cleanup? Y/n" {
            send "n\r"
            exp_continue
      }
}

Answer 1

The expect command matches against tcl string match style wildcard patterns by default, so [Y/n] is trying to match one of the characters Y, forward slash or n.

Solutions:

1. Add more backslashes:

append item " and do cleanup? \\\[Y/n\\\]"

so it turns into \[Y/N\].

2. Use braces instead:

append item { and do cleanup? \[Y/n\]}

to prevent the substitution of backslashes.

3. Tell expect to do an exact match by using the -ex option before each pattern:

#!/usr/bin/expect -f

set timeout -1

spawn ./question.sh

set item "Deleted Item with ID: "
append item [lindex $argv 0]
append item " and do cleanup? \[Y/n\]"

expect -ex "Would you like to specify inputs and execute the script? \[Y/n\]"
send -- "Y\r"

expect {

      -ex $item {
            send "Y\r"
            exp_continue
      }
      -ex " and do cleanup? \[Y/n\]" {
            send "n\r"
            exp_continue
      }
}