The bash shell has variable PS1 which controls how the prompt is displayed.

You can find many examples of how to customise the prompt: https://duckduckgo.com/?q=Bash+PS1

For a long time I have kept this PS1 around from Raspbian, but today I wondered what everything actually did:

PS1="\[\033]0;\u@\h: \w\007\]\[\e[1;32m\]\h\[\e[1;32m\]:\[\e[1;34m\]\w \[\e[0m\]\\$ "

You can just paste this into bash to see what it looks like. It will show something like this, with your computer’s name as hostname and your cursor blinking at _:

hostname:~ $ _

If you change to a directory, then that directory name is added to the prompt, eg:

hostname:~ $ cd Downloads
hostname:~/Downloads $ _

I started looking into this, and the first part of it baffled me:

PS1="\[\033]0;\u@\h: \w\007\]

So I skipped that for now and focused on the rest, I already knew what these did:

\[\e[1;32m\]\h\[\e[1;32m\]:\[\e[1;34m\]\w \[\e[0m\]\\$ 

The bash colours are explained better by others (with actual colour) at pages such as:

• https://www.shellhacks.com/bash-colors/
• https://www.lihaoyi.com/post/BuildyourownCommandLinewithANSIescapecodes.html
• or just search around for “bash colors” or “ansi colors”

They are explained as:

\[  start non-printing characters
  \e[1;32m  bold green
          \]  end non-printing characters
            \h  hostname
              \[  start non-printing characters
                \e[1;32m  set text color to bold/bright green
                        \]  end non-printing characters
                          :  literal colon character ":"
                           \[  start non-printing characters
                             \e[1;34m  set text color to bold/bright blue
                                     \]  end non-printing characters
                                       \w  current working directory, with home abbreviated as ~
                                         _  a literal space character " "
                                          \[  start non-printing characters
                                            \e[0m  reset text to no color
                                                 \]  end non-printing characters
                                                   \\$

And the last line creates the prompt. If effective UID is 0 (eg: you’ve done sudo -s to open a root shell) then it becomes #, otherwise if you’re a non-root user then it is $.

Now, back to the first part:

PS1="\[\033]0;\u@\h: \w\007\]

We can already spot some of these, such as \] and \] to delimit non-printing characters, \w for the current working directory with ~ for home, and I happen to know \u@\h shows username@hostname. But what are the rest?

The answer is hidden over here on the Ask Ubuntu StackExchange site.

The \033] is an Octal character named ESC, and the ] after it means an “Operating System Command” or OSC.

We can see in the xterm Control Sequence manual that 0; means “Set Text Parameters” and “Change Icon Name and Window Title”. The username@hostname: cwd now makes sense, that’s the graphical terminal window’s title text!

The \007 is an ASCII BEL character, which is used to end the OSC.

So looking at it again:

PS1="\[\033]0;\u@\h: \w\007\]

We can explain this as:

     \[  begin a sequence of non-printing characters
       \033 octal 033 "Esc"
           ]  OSC
            0;  change icon and window name to:
              \u@\h  username@hostname
                   :  a literal colon and space ": "
                     \w  working directory, with home abbreviated as ~
                       \007  octal 007 terminal bell, end the OSC
                           \]  end non-printing characters

The answer I linked on Ask Ubuntu isn’t the most upvoted answer, but it is the correct answer.

Looking at the author of the answer, it shouldn’t come as a surprise that it’s the correct answer.

It’s written by Thomas Dickey, a long-time open source software developer, and maintainer of many low-level pieces of software such as ncurses and xterm itself!