15

I'm new to bash and would like my prompt to show something that in tcsh was trivial, yet after a good google search I still cannot do.

I would like my prompt to include only the current and parent directories like this:

/parent/currentdir $

In tcsh this is achieved by:

set prompt = "%C2 %"

However in bash so far I have only found that I have to parse pwd to obtain the same output.

Isn't there a simpler way, like doing:

export PS1="$(some_command) $" 
  • 2
    In theory, PS1='\w \$'; PROMPT_DIRTRIM=2 should give you the bash equivalent, but that doesn't work properly on my system. – Mikel Jul 18 '15 at 23:15
  • It doesn't work at all on mine: GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin14). – twalbaum Aug 7 '15 at 23:19
  • PROMPT_DIRTRIM was introduced in Bash 4. I just tested on Ubuntu 16.04 under WSL and it worked great! – Mike Branski Dec 8 '17 at 18:08
18

Bash's prompt control features are rather static. If you want more control, you can include variables in your prompt; make sure you haven't turned off the promptvars option.

PS1='${PWD#"${PWD%/*/*}/"} \$ '

Note the single quotes: the variable expansions must happen at the time the prompt is displayed, not at the time the PS1 variable is defined.

If you want more control over what is displayed, you can use command substitutions. For example, the snippet above loses the ~ abbreviation for the home directory.

PS1='$(case $PWD in
        $HOME) HPWD="~";;
        $HOME/*/*) HPWD="${PWD#"${PWD%/*/*}/"}";;
        $HOME/*) HPWD="~/${PWD##*/}";;
        /*/*/*) HPWD="${PWD#"${PWD%/*/*}/"}";;
        *) HPWD="$PWD";;
      esac; printf %s "$HPWD") \$ '

This code is rather cumbersome, so instead of sticking it into the PS1 variable, you can use the PROMPT_COMMAND variable to run code to set HPWD and then use that in your prompt.

PROMPT_COMMAND='case $PWD in
        $HOME) HPWD="~";;
        $HOME/*/*) HPWD="${PWD#"${PWD%/*/*}/"}";;
        $HOME/*) HPWD="~/${PWD##*/}";;
        /*/*/*) HPWD="${PWD#"${PWD%/*/*}/"}";;
        *) HPWD="$PWD";;
      esac'
PS1='$HPWD \$'

Since the shortened prompt only changed on a directory change, you don't need to recalculate it each time a prompt is displayed. Bash doesn't provide a hook that runs on a current directory change, but you can simulate it by overriding cd and its cousins.

cd () { builtin cd "$@" && chpwd; }
pushd () { builtin pushd "$@" && chpwd; }
popd () { builtin popd "$@" && chpwd; }
chpwd () {
  case $PWD in
    $HOME) HPWD="~";;
    $HOME/*/*) HPWD="${PWD#"${PWD%/*/*}/"}";;
    $HOME/*) HPWD="~/${PWD##*/}";;
    /*/*/*) HPWD="${PWD#"${PWD%/*/*}/"}";;
    *) HPWD="$PWD";;
  esac
}
PS1='$HPWD \$'

Note that you don't need to, and should not, export PS1, since it's a shell setting, not an environment variable. A bash PS1 setting wouldn't be understood by other shells.

P.S. If you want a nice interactive shell experience, switch to zsh, where all of these (prompt % expansions largely encompassing tcsh's, chpwd, etc.) are native features.

PS1='%2~ %# '
  • 2
    This should have been the accepted and most upvoted answer. – LarsH Jun 21 '16 at 12:28
2

The syntax for obtaining the parent and current directories is taken from Munai's answer.

However, as noted by Gilles, that code only shows the current directory at the time .bashrc is loaded, but it won't change as you navigate the system to other folders.

Having this in your .bashrc file makes the prompt automatically updated to your current directory:

prompt_command () {
    PS1='$(basename $(dirname "$PWD"))/$(basename "$PWD") $ '
}
PROMPT_COMMAND=prompt_command
  • 1
    Is defining prompt_command() supposed to do something, on its own? It doesn't for me. Did you mean to also use prompt_command() in redefinitions of cd & co, like Gilles did? Or did you mean PROMPT_COMMAND='...'? – LarsH Jun 21 '16 at 12:27
  • 2
    Also, this command fails when $PWD contains a space. – LarsH Jun 21 '16 at 12:37
  • 1
    Thank you for bringing me back to this. Quoted the $PWDs to allow for spaces and included the final command. My current prompt is more complex than this, therefore the need for the prompt_command definition. Otherwise, PS1=... works on its on. – twalbaum Jul 8 '16 at 20:36
  • Any ideas for cleaning up the output when navigating to /? As written, you get /// $ – ezrock Nov 10 '17 at 18:14
0

Prompt string can be easily changed in bash by editing the shell variable PS1. It stands for Prompt String 1. More info here.

For now fire up your bash shell.

vi ~/.bashrc

Append the PS1 definition in the file

`export PS1="$(basename $(dirname $PWD))/$(basename $PWD)"`

More tutorials here and here, to help you tweak it even more.

  • 1
    I understand how to modify the prompt. My question is how to get only the current and parent directories, not the whole path. – twalbaum Jul 18 '15 at 20:50
  • @twalbaum edited my answer – Munai Das Udasin Jul 18 '15 at 20:59
  • glad to help @twalbaum :) – Munai Das Udasin Jul 18 '15 at 21:04
  • 1
    This sets the prompt to the current directory at the time .bashrc is loaded, the prompt won't change if you cd into another directory! @twalbaum – Gilles Jul 19 '15 at 21:16
  • @Gilles it does for me. – twalbaum Jul 19 '15 at 21:19
0

May be simpler one with "~" for Home directory.

function PWDN {
  echo "${PWD/#$HOME/~}" | rev | cut -d "/" -f1 -f2 | rev
}
0
export PS1='[\u@\h $(basename $(dirname ${PWD}))/$(basename ${PWD})]\$ '
export PROMPT_COMMAND='echo -ne "\033]0;$(basename $(dirname $PWD))/$(basename ${PWD})\007"'

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