Shell Programming and Scripting

#!/bin/ksh

usage ()
{
     echo " Usage: $0 <opt1> <opt2> <opt3> <opt4>"
}

if [ $# -lt 3 ]; then
        usage
        exit;
fi

prog -a $1 -b $2 -c $3 -d $4 2>&1 | tee -a ~/$1.log

#!/bin/ksh

usage ()
{
     echo " Usage: $0 <opt1> <opt2> <opt3> <opt4>"
}

if [ $# -lt 3 ]; then
        usage
        exit;
fi

if [ -z $4 ]; then
  prog -a $1 -b $2 -c $3 2>&1 | tee -a ~/$1.log
else
  prog -a $1 -b $2 -c $3 -d $4 2>&1 | tee -a ~/$1.log
fi

#!/bin/ksh

usage ()
{
     echo " Usage: $0 <opt1> <opt2> <opt3> [<opt4>]"
}

[[ $# -lt 3 ]] && { usage; exit; }

prog -a $1 -b $2 -c $3 ${4:+-d $4} 2>&1 | tee -a ~/$1.log

...
if [ -z "$4" ]; then
...

${parameter:+word}

       If  parameter  is  set  and is non-null, substitute word. Otherwise
       substitute nothing.

usage ()
{
     echo " Usage: $0 -a value -b value -c value [ -d value ]" >&2
     exit 1
}

#####################
a=""
b=""
c=""
d=""
# parse options
while [ $# -gt 0 ]
do
        case "$1" in
                -a) a="$2" ; shift ;;
                -b) b="$2" ; shift ;;
                -c) c="$2" ; shift ;;
                -d) d="$2" ; shift ;;
                --) shift; break ;;
                -*) usage ;;
                *) break ;;  # arguments ...
        esac
        shift
done
# now $* include arguments
[ "$a" = "" ] && usage
[ "$b" = "" ] && usage
[ "$c" = "" ] && usage

if [ "$d" = "" ] ; then
      prog -a "$a" -b "$b" -c "$c" 2>&1 | tee -a ~/"$a".log 
else
     prog -a "$a" -b "$b" -c "$c" -d "$d" 2>&1 | tee -a ~/"$a".log
fi