Print return value after program execution

I am wondering how to set option to auto print return value after every program execution in terminal without typing echo $?.

Is it something that can be setup? Codeblocks has that feature.

Yes, there are two ways. One is to set PROMPT_COMMAND in .bashrc, the other - to set command substitution in PS1 for the echo $? command.

Method 1:

From the bash manual page:

PROMPT_COMMAND

      If set, the value is executed as a command prior to issuing each
      primary prompt.

Whatever you set this variable to, will be run before drawing the prompt each time. Demo:

$> PROMPT_COMMAND=" echo 'Last command exited with'  \$? 'code'  "
Last command exited with 0 code
$> ls /etc/passwd > /dev/null
Last command exited with 0 code
$> ls /etc/asdf > /dev/null
ls: cannot access /etc/asdf: No such file or directory
Last command exited with 2 code
$> 

Note the use of \$? . For permanent change, save it in .bashrc

Method 2

Suppose my PS1 prompt is set like this:

PS1='
user@ubuntu:$> '

If I want to run some program each time this prompt is redrawn on the screen (which is after each preceding command runs), I would need to use command substitution $(. . .) and set it in the prompt like so:

PS1=' [ $? ] 
user@ubuntu: $> '

Demo:

$> PS1=' [ $? ]
> $>_ '
 [ 0 ]
$>_ ls /etc/passwd > /dev/null
 [ 0 ]
$>_ ls /etc/asdf > /dev/null                                                                                                      
ls: cannot access /etc/asdf: No such file or directory
 [ 2 ]
$>_ 

Notice that I split my PS1 into two lines, top will have [ exitcode ] and bottom $> <blank space>' . That is why there is > before $> ' on the second line (The leading > is PS2 prompt for multiline commands ) . Alternatively, you could do something like this ( notice the $'...' structure):

  $> PS1=$'[ $? ] \n$> '                                                                                                  
[ 0 ] 
$> 

A method which I picked from the Arch Wiki is to trap ERR. trap is used in Bash to run commands when a signal is received, or for certain other events. An ERR trap is ran whenever the current command line terminates with an error - the return value is not 0. (If it did terminate normally, the return value would obviously be 0.)

So, for example:

trap 'printf "\ncode %d\n\n" $?' ERR

Then:

$ echo foo
foo
$ false

code 1

$

(Note: no message after the echo command which ran successfully - What does it mean when I type a command and the terminal does nothing?)

The Arch Wiki tip went ahead and colorized the message, so that you get a noticeable yellow message:

EC() { echo -e '\e[1;33m'code $?'\e[m\n'; }
trap EC ERR

Effect:

In effect, all I need to do is keep an eye out for a yellow code in the output to know a command failed.