unix shellscript for renaming multiple files by removing a string from all filenames

# folder: no trailing slash $1 
# str:    string to remove  $2

folder=$1
str=$2
echo $folder $str

files=`ls -1 $folder`
 for file in $files ; do
  echo $file
  tc=`echo $file | sed s/$str//`
  echo $tc
  if [ -f $folder/$file ];
  then
    mv $folder/$file $folder/$tc
  #echo $tc
  #echo $folder/$file $folder/$tc
  fi
done

exit 1