This is the command output need to be matched:
[snr_core.serconsole.con info] Telnet console listening to port 42365.
(the port number changes every time)

Code to test it:

#!/tools/AGRtools/bin/expect
exp_internal 1

set timeout 10

spawn bash
set bashId $spawn_id

send_user -i $bashId "\n"
send_user -i $bashId "\[snr_core.serconsole.con info\] Telnet console listening to port 42365.\n"
expect -i $bashId -re "\[snr_core.serconsole.con info\] Telnet console listening to port \[0-9]*\." {send_user "The output is $expect_out(0,string)\n"}

====================================
It send_user a line, the same as the expected output, then catch it and display $expect_out(0,string).

This is the debug output:

spawn bash
parent: waiting for sync byte
parent: telling child to go ahead
parent: now unsynchronized from child
spawn: returns {115854}

[snr_core.serconsole.con info] Telnet console listening to port 42365.

expect: does "" (spawn_id exp4) match regular expression "[snr_core.serconsole.con info] Telnet console listening to port [0-9]*."? no
antxec10:/user_workspace/master/tools/AcpTestTool:
expect: does "\u001b]0;ecuser@antxec10:~/user_workspace/master/tools/AcpTestTool\u0007\u001b[?1034hantxec10:/user_workspace/master/tools/AcpTestTool:" (spawn_id exp4) match regular expression "[snr_core.serconsole.con info] Telnet console listening to port [0-9]*."? no
expect: timed out

I also tried different escape sequences, brace, double/triple backslash etc., no luck.

Appreciate for any help

isn't it possible an invisible character produced ?

expect -i $bashId -re "\[snr_core.serconsole.con\s+info\]\s+Telnet\s+console\s+listening\s+to\s+port\s+\[0-9]+\."  {send_user "The output is $expect_out(0,string)\n"}

This code to match the send_user line, there is no invisible character.
I try

expect -i $bashId -re "\[snr_core.serconsole.con\s+info\]\s+Telnet\s+console\s+listening\s+to\s+port\s+\[0-9]+\."  {send_user "The output is $expect_out(0,string)\n"}

It does not work.

send_user just logs text to stdout it doesn't send it to the bash command as input, so you cant use expect to test for it.

This the real output:
>>> run_test_analysis()
[Info] Running DataCapture and Validation for Test(1).
[Info] Test(1) passed.
>>>

command run_test_analysis() will output Test(1) passed or failed. I want to catch the line:
[Info] Test(1) xxxxx.

.....
exp_send -i $bashId "run_test_analysis()\r"
expect -i $bashId -re "\[Info\] Test\(1\) .*\."    
set testResult [lindex [split $expect_out(0,string) " ."] end-1]
send_user "\nTest(1): $testResult\n"
....

I use different sequences in expect:
expect -i $bashId -re "\\\[Info\\\] Test\(1\) .\."
expect -i $bashId -re "\\[Info\\] Test\(1\) .\."
expect -i $bashId -re "\[Info\] Test\(1\) ."
expect -i $bashId -re ".*Test(1)."
expect -i $bashId -re ".* Test\(1\) .*"
expect -i $bashId -re ".Test(1) \[a-z]\."

Also tried global pattern match, no one work.
Can someone shed some light on it?
Thanks