#!/bin/sh

# SubStr.sh
# Mon Mar 30 17:10:41 PST 2009
# Chieh Cheng
# http://www.CynosureX.com/

# GNU General Public License (GPL) Version 2, June 1991

  scriptName=`basename "$0"`

  extractEnd ()
  {
    string="$1"
    begin=$2

    length=`StrLen.sh "${string}"`
    chars=`expr ${length} - ${begin}`
    regExp="`genRegEx ${chars}`$"
    echo "${string}" | grep -o "${regExp}" | head -1
  }

  genRegEx ()
  {
    chars=$1
    expression=""
    count=0
    while [ ${count} -lt ${chars} ]
    do
      expression="${expression}."
      count=`expr ${count} + 1`
    done
    echo "${expression}"
  }

  usage ()
  {
    echo "  Usage:   ${scriptName} \"string\" \"begin index\" [ \"end index\" ]"
    echo
    echo "             begin index - inclusive"
    echo "             end   index - exclusive"
  }

  if [ $# -ge 2 ] && [ $# -le 3 ]
  then
    str="$1"
    begin=$2

    if [ $# -eq 3 ]
    then
      end=$3
    else
      end=999999999999999999
    fi

    if [ ${begin} -gt ${end} ]
    then
      tmp=${end}
      end=${begin}
      begin=${tmp}
    fi

    if [ ${begin} -ne ${end} ]
    then
      len=`StrLen.sh "${str}"`

      if [ ${begin} -lt ${len} ]
      then
        if [ ${end} -le ${len} ]
        then
          chars=${end}
          regExp="^`genRegEx ${chars}`"
          result=`echo "${str}" | grep -o "${regExp}" | head -1`

          extractEnd "${result}" ${begin}
        else
          extractEnd "${str}" ${begin}
        fi
      fi
    fi
  else
    usage
  fi