2.sh

#!/usr/bin/env bash
set -eu
echo '
    spawn ./1.sh
    expect >
    send cmd1\n
    expect "\nd "   ;# it matches
    send quit\n
' | expect -d

gistfile1.txt

$ ./2.sh
expect version 5.45                                                                   [6/91679]
argv[0] = expect  argv[1] = -d
set argc 0                                                                                     
set argv0 "expect"                             
set argv ""                                    
executing commands from command file           
spawn ./1.sh                                   
parent: waiting for sync byte
parent: telling child to go ahead                                                              
parent: now unsynchronized from child
spawn: returns {31239}
                                                                                               
expect: does "" (spawn_id exp6) match glob pattern ">"? no
>                                              
expect: does "> " (spawn_id exp6) match glob pattern ">"? yes
expect: set expect_out(0,string) ">"           
expect: set expect_out(spawn_id) "exp6"
expect: set expect_out(buffer) ">"             
send: sending "cmd1\n" to { exp6 }

expect: does " " (spawn_id exp6) match glob pattern "d"? no
cmd1

expect: does " cmd1\r\n" (spawn_id exp6) match glob pattern "d"? yes
expect: set expect_out(0,string) "d"
expect: set expect_out(spawn_id) "exp6"
expect: set expect_out(buffer) " cmd"
send: sending "quit\n" to { exp6 }