I'm sorry! On rereading your original post, I realize you are using double quotes:

 $exp->send("$command ; echo COMMAND_RET:$? | sed 's/^/COMMAND_OUT: /g
+'; echo -n END_; echo EXPECT\n");

[download]

So your command is not actually what you send over the wire. Use 

my $cmd = "$command ; echo COMMAND_RET:$? | sed 's/^/COMMAND_OUT: /g';
+ echo -n END_; echo EXPECT\n";
warn "Sending command [$cmd]";
$exp->send($cmd);

[download]

for debugging such issues. Personally, when dealing with interpolating data into strings, I prefer sprintf over plain interpolation:

my $cmd = sprintf q{%s; echo COMMAND_RET:$? | sed 's/^/COMMAND_OUT: /g
+'; echo -n END_; echo EXPECT\n}, $command;
warn "Sending command [$cmd]";
$exp->send($cmd);

[download]

In reply to Re^3: Incorrect value 0 reported in command execution return value variable $?, when trying with expect->send command by Corion
in thread Incorrect value 0 reported in command execution return value variable $?, when trying with expect->send command by Davewhite

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