Bash string slice

string_slice.sh

string_slice() 
{
  [ -z $2 ] && echo "Usage: string_slice \"string\" start [end]" && return
  
  string=$1
  local len="${#string}"
  local start="$2"
  local end="$3"
  :${end:=0}
  
  if [ ${start} -lt 0 ]; then
    start=$((${len} + ${start}))
  fi
  if [ ${end} -le 0 ]; then
    end=$((${len} + ${end}))
  fi
  start=$((${start} + 1))
  (echo "${string}" | cut -c ${start}-${end}) 2> /dev/null
}