For convenience, I'll define the prompt and command first:

   set command date      ;# our remote command
   set prompt  "% "      ;# our shell or whatever prompt we have

Now we can do useful things:

   expect $prompt        ;# wait for prompt
   send   $command\r     ;# send command
   expect $prompt\r\n    ;# discard command echo

Finally, match and save the result and discard the next prompt:

   expect -re (.*)\r\n$prompt\r\n

Now the result is in $expect_out(1,string).

If you want to read more about this, start on page 113 of [BOOK Exploring Expect].  This idiom is difficult for some programmers.  The point is that [Expect] never gives direct access to "the result of a (foreign) command"; it simply transacts [send]-expect dialogues, and the developer
has to know how to subtract out prompts, newlines, and other conventional decorations.

[PS]: If the result might be more than 2000 characters, you'll need to use the [match_max] command to increase the buffer space.

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"[Remote input-output with Expect]"
gives
a model for line-oriented result access.

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The example above didn't work for me (yes, I know that the above is not a complete programme).
The following is an example which works on my [FreeBSD] 4.7 machine.

   set prompt ">>> "   ;# our shell or whatever prompt we have
   set command "date"  ;# the command whose output we want to catch

   spawn bash          ;# spawn the bash 

   expect "$prompt"    ;# wait for prompt

   send   "$command\r" ;# send command
   expect "$command\r" ;# discard command echo

   expect -re "(.*)\r" ;# match and save the result


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Get in the habit of using [exp_send] instead of [send] when using Expect.  If you later decide to add [Tk] to your [script] you will not collide with Tk's send command.
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[Category Expect]