I believe this is what they call “prompt engineering”.
username@hostname:~/pwd
rm /
rm: cannot remove '/': Is a directory
username@hostname:~/pwd
^C
username@hostname:~/pwd
I set the color of the colon : to the 8-bit color corresponding to the Exit status of the last executed command ($?). 0 is success, which maps to black, which is usually the background color, which makes it invisible until copied and pasted somewhere else. Any other value (1-255) makes it visible.
Everything else is pretty basic.
bash
PS1='\[\e[1;32m\]\u@\h\[\e[38;5;$?m\]:\[\e[34m\]\w\[\e[0m\] '
You might see \033 for octal character 33 instead of \e for escape. Hexadecimal \x1b and decimal \27 didn’t work.
The outer enclosing square brackets \[\] around each escape sequence may appear to be optional at first, but after testing, I found that omitting them causes weird behavior.
zsh
PS1='%B%F{green}%n@%m%b%F{%?}:%B%F{blue}%~%f%b '
| bash1 | zsh2 | ||
|---|---|---|---|
| Start boldface mode Set foreground color green | \e[1;32m | ||
| Start boldface mode | %B | ||
| Set foreground color green | %F{green} | ||
| username of the current user | \u | %n | username |
literal @ character | @ | @ | @ |
| hostname up to the first ’.‘. | \h | %m | hostname |
| stop boldface mode | %b | ||
Set foreground color $? | \e[38;5;$?m | %F{%?} | |
literal : character | : | : | : |
| Set foreground color blue | \e[34m | %F{blue} | |
$PWD with $HOME replaced by a ’~‘. | \w | %~ | ~/pwd |
| All attributes become turned off | \e[0m | ||
| stop using a different foreground color | %f | ||
| stop boldface mode | %b | ||
| literal space character | | | |