Whodo - Display who do what

The script

##########################################################################
# Description
#        Show who is logged on and what he is doing.
#        This program works like the System V "whodo" command.
##########################################################################

PN=`basename "$0"`                # Program name
VER=`echo '$Revision: 1.2 $' | cut -d' ' -f2`

Usage () {
    echo "$PN - who is doing what, $VER (stv '95)
usage: $PN [-l] [-h] [user]
    -h: suppress the heading
    -l: long form of output" >&2
    exit 1
}

Msg () {
    for i
    do echo "$PN: $i" >&2
    done

}

Fatal () { Msg "$@"; exit 1; }

LongOutput=no
Header=yes
while [ $# -gt 0 ]
do
    case "$1" in
        -l)     LongOutput=yes;;
        -h)     Header=no;;
        --)     shift; break ;;
        -*)     Usage;;
        *)      break ;;                # First file name
    esac

    shift
done

[ $# -gt 0 ] && User="$1"

if [ "$LongOutput" = no ]
then
    [ $Header = yes ] && {
     date
        uname -n
    }

    # Sample output of who:

    #    heiner   console Apr 26 08:18
    who |
        while read Name Tty Mon Day Time Host Rest
  do
            [ -n "$User" -a "$User" != "$Name" ] && continue
         echo "
$Tty    $Name   $Time"
      case "$Tty" in
                *tty*)  T=`echo "$Tty" | sed -e 's:.*tty\(..\).*:\1:'`;;
                *)      T=`echo "$Tty" | sed -e 's:/dev/\(..\).*:\1:'`;;
      esac


     # Sample output of ps -c:
     #   PID TT STAT  TIME COMMAND
     #   327 p2 IW    0:19 ksh
         ps -ct"$T" | tail +2 |
                while read pid tty stat time command
          do
                 echo "    $Tty  $pid    $time   $command"
          done

  done
else
    # Long form: use "w" output format
    if [ $Header = yes ]
    then FirstLine=1
    else FirstLine=3
    fi

    if [ -z "$User" ]
    then
        w
    else
        w | grep "$User"
    fi | tail +$FirstLine

fi