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Bash-like Customizable Prompt in Korn Shell

Bash has built-in support for extensive PS1 prompt customization using parameterless macros. As a result many people customize their shell prompts. There is no equivalent built-in support for PS1 customization in ksh93 but such support can easily be added using a discipline function. This post provides an example of such a PS1 discipline function.

Add the following discipline function to your ~/.kshrc and ensure that ~/.kshrc is included in your ~/.profile shell startup script which, by the way, only gets executed at login if ksh93 is your default shell.

function PS1.set
{
    typeset prefix remaining=${.sh.value} var= n= k=
    set -A .sh.lversion ${.sh.version}
 
    while [[ $remaining ]]
    do
        prefix=${remaining%%'\'*}
        remaining=${remaining#$prefix}
        var+="$prefix"
        
        case ${remaining:1:1} in
            A)    var+="\$(printf '%(%R)T')";;
            @)    var+="\$(printf '%(%H:%M %p)T')";;
            d)    var+="\$(printf '%(%a %b:%d)T')";;
            e)    var+="\$'\e'";;
            h)    var+=$(hostname -s);;
            H)    var+=$(hostname);;
            j)    var+="\$(jobs | wc -l)";;
            l)    var+="\$(basename \"\$(tty)\")";;
            n)    var+=$'\n';;
            r)    var+=$'\r';;
            s)    var+="\$(basename \"\$0\")";;
            t)    var+="\$(printf '%(%H:%M:%S)T')";;
            T)    var+="\$(printf '%(%I:%M:%S)T')";;
            u)    var+=$USER;;
            v)    var+="\${.sh.lversion[2]}";;
            V)    var+="\${.sh.lversion[2]} (\${.sh.lversion[1]})";;
            w)    var+="\$(pwd)";;
            W)    var+="\$(basename \"\$(pwd)\")";;
          '#')    var+=!;;
            !)    var+=!;;
          '$')    if (( $(id -u) == 0 ))
                  then 
                      var+='#'
                  else 
                      var+='$'
                  fi;;
          '\')    var+='\\';;
      '['|']')    ;;
        [0-7])    case ${remaining:1:3} in
	               [0-7][0-7][0-7])   k=4;;
                            [0-7][0-7])   k=3;;
                                     *)   k=2;;
                  esac
                  eval n="\$'"${remaining:0:k}"'"
                  var+=$n
                  remaining=${remaining:k}
                  continue ;;
           "")    ;;
            *)    var+='\'${remaining:0:2};;
        esac
        remaining=${remaining:2}
    done
    .sh.value=$var
}


Dave Korn originally published the guts of this discipline function some 11 years ago. I have merely extended the code to include all the Bash PS1 prompt parameterless macros that I am aware of.

Here is a list of the currently supported parameterless macros:

\d : the date in "Weekday Month Date" format (e.g., "Tue May 26")
\e : an ASCII escape character (033)
\h : the hostname up to the first '.'
\H : the hostname
\j : the number of jobs currently managed by the shell
\l : the basename of the shell’s terminal device name
\n : a newline
\r : a carriage return
\s : the name of the shell (basename of $0)
\t : the current time in 24-hour HH:MM:SS format
\T : the current time in 12-hour HH:MM:SS format
\@ : the current time in 12-hour am/pm format
\A : the current time in 24-hour HH:MM format
\u : the username of the current user
\v : the version of ksh93
\V : the version of ksh93 and supported options
\w : the current working directory, with $HOME abbreviated with a tilde
\W : the basename of the current working directory, with $HOME abbreviated with a tilde
\! : the history number of this command
\# : the command number of this command
\$ : if the effective UID is 0, #, otherwise $
\nnn : the character corresponding to the octal number nnn
\\ : a backslash
\[ : begin a sequence of non-printing characters
\] : end a sequence of non-printing characters

Here is a screenshot showing some examples of how to customize the ksh93 PS1 prompt using the above PS1 discipline function:

Note that discipline functions are a feature of later versions of ksh93 and are NOT supported in the original Korn Shell (ksh88) or clones of the Korn Shell such as pdksh.

Enjoy!

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