2.4)  How do I get the current directory into my prompt?

      It depends which shell you are using.  It's easy with some
      shells, hard or impossible with others.

      C Shell (csh):
        Put this in your .cshrc - customize the prompt variable the
        way you want.

            alias setprompt 'set prompt="${cwd}% "'
            setprompt           # to set the initial prompt
            alias cd 'chdir \!* && setprompt'
        
        If you use pushd and popd, you'll also need

            alias pushd 'pushd \!* && setprompt'
            alias popd  'popd  \!* && setprompt'

        Some C shells don't keep a $cwd variable - you can use
        `pwd` instead.

        If you just want the last component of the current directory
        in your prompt ("mail% " instead of "/usr/spool/mail% ")
        you can use

            alias setprompt 'set prompt="$cwd:t% "'
        
        Some older csh's get the meaning of && and || reversed.
        Try doing:

            false && echo bug

        If it prints "bug", you need to switch && and || (and get
        a better version of csh.)

      Bourne Shell (sh):

        If you have a newer version of the Bourne Shell (SVR2 or newer)
        you can use a shell function to make your own command, "xcd" say:

            xcd() { cd $* ; PS1="`pwd` $ "; }

        If you have an older Bourne shell, it's complicated but not
        impossible.  Here's one way.  Add this to your .profile file:

                LOGIN_SHELL=$$ export LOGIN_SHELL
                CMDFILE=/tmp/cd.$$ export CMDFILE
                # 16 is SIGURG, pick a signal that's not likely to be used
                PROMPTSIG=16 export PROMPTSIG
                trap '. $CMDFILE' $PROMPTSIG

        and then put this executable script (without the indentation!),
        let's call it "xcd", somewhere in your PATH

                : xcd directory - change directory and set prompt
                : by signalling the login shell to read a command file
                cat >${CMDFILE?"not set"} <<EOF
                cd $1
                PS1="\`pwd\`$ "
                EOF
                kill -${PROMPTSIG?"not set"} ${LOGIN_SHELL?"not set"}

        Now change directories with "xcd /some/dir".

      Korn Shell (ksh):

        Put this in your .profile file:
                PS1='$PWD $ '
        
        If you just want the last component of the directory, use
                PS1='${PWD##*/} $ '

      T C shell (tcsh)

        Tcsh is a popular enhanced version of csh with some extra
        builtin variables (and many other features):

            %~          the current directory, using ~ for $HOME
            %/          the full pathname of the current directory
            %c or %.    the trailing component of the current directory

        so you can do

            set prompt='%~ '

      BASH (FSF's "Bourne Again SHell")
        
        \w in $PS1 gives the full pathname of the current directory,
        with ~ expansion for $HOME;  \W gives the basename of
        the current directory.  So, in addition to the above sh and
        ksh solutions, you could use

            PS1='\w $ ' 
        or
            PS1='\W $ '