#!/bin/bash
# rfe.sh: Renaming file extensions.
#
#         rfe old_extension new_extension
#
# Example:
# To rename all *.gif files in working directory to *.jpg,
#          rfe gif jpg


E_BADARGS=65

case $# in
  0|1)             # The vertical bar means "or" in this context.
  echo "Usage: `basename $0` old_file_suffix new_file_suffix"
  exit $E_BADARGS  # If 0 or 1 arg, then bail out.
  ;;
esac


for filename in *.$1
# Traverse list of files ending with 1st argument.
do
  mv $filename ${filename%$1}$2
  #  Strip off part of filename matching 1st argument,
  #+ then append 2nd argument.
done

exit 0