command execute with error when use expect in shell script while work fine in pure shell - bash

Question

I try to start all the exited docker containers deployed in separated servers, so basically i should execute the essential command below
[ $(docker ps -a | grep Exited | wc -l) -ne 0 ] && docker start $(docker ps -a | grep Exited | cut -d' ' -f1)
It worked fine like in pure linux shell , but then error occured(show below) when i try to use expect to "send" the "essential" command. (local ip is 241,remote end is 209)
[root#localhost start_shell_dir]# spawn ssh root#192.168.1.209
root#192.168.1.209's password:
Last login: Fri Oct 15 22:23:25 2021 from 192.168.1.241
[root#localhost ~]# invalid command name "0"
while executing
"0 -ne 0 "
invoked from within
"send "[ 0 -ne 0 ] && docker start ""
The error log shows i have already log in the remote machine, and something wrong when i execute the docker command.
Glenn jackman from the comment area shows me the basic rule for tcl,then i realize expect does command substitutions before sending real command. We may see it from execute bash -x script.sh .
[root#localhost start_shell_dir]# bash -x startContainer.sh
+ read ip pass
+ read ip pass
+ /usr/bin/expect
[root#localhost start_shell_dir]# ++ docker ps -a
++ grep Exited
++ wc -l
++ docker ps -a
++ grep Exited
++ cut '-d ' -f1
spawn ssh root#192.168.1.209
root#192.168.1.209's password:
Last login: Fri Oct 15 22:37:56 2021 from 192.168.1.241
[root#localhost ~]# invalid command name "0"
while executing
"0 -ne 0 "
invoked from within
"send "[ 0 -ne 0 ] && docker start ""
Anyway, the final command that work for me is the command showed below(replace double quotes with braces and with backslash before $() to keep it as an ordinary character rather than pre-parse it).
send {[ \$(docker ps -a | grep Exited | wc -l) -ne 0 ] && docker start \$(docker ps -a | grep Exited | cut -d' ' -f1)}
#!/bin/bash
# my original script with error
while read ip pass
do
{
/usr/bin/expect <<-END
spawn ssh root#$ip
expect {
"yes/no" { send "yes\r";exp_continue }
"password:" { send "$pass\r" }
}
expect "#"
send "[ $(docker ps -a | grep Exited | wc -l) -ne 0 ] && docker start $(docker ps -a | grep Exited | cut -d' ' -f1)"
expect eof
END
}&
done<apps_ip.txt

Answer 1

Like the shell, Tcl (and expect) allows interpolation with double quotes. Tcl uses square brackets for command substitution (in the same way that the shell uses $(...))
Use curly braces to protect the contents of that string (analogous to the shell's single quotes):
send {[ $(docker ps -a | grep Exited | wc -l) -ne 0 ] && docker start $(docker ps -a | grep Exited | cut -d' ' -f1)}
#....^.............................................................................................................^
# and don't forget to hit Enter
send "\r"
See https://www.tcl-lang.org/man/tcl8.6/TclCmd/Tcl.htm for the few syntax rules of Tcl.