#!/bin/bash

printHelp ()
{
  echo "Usage: $0 -f find -r replace FILES_TO_RENAME*"
  echo -e "\t-f The text to find in the filename"
  echo -e "\t-r The text used to replace with in the filename"
  exit 1
}

while getopts "f:r:" opt; do
  case "$opt" in
    r ) replace="$OPTARG"    ;;
    f ) fnd="$OPTARG"        ;;
    ? ) printHelp            ;;
  esac
done

shift $(( $OPTIND - 1 ))

if [ -z $replace ] || [ -z $fnd ]
then
  echo "Need a string to find and a string to replace";
  printHelp
fi

for i in $@
do
  newname=$(echo $i | sed "s/$fnd/$replace/")
  mv $i $newname
  echo "Renamed file $i to $newname"
done