ext-modify.sh

#!/bin/bash
if [ $1 == 'help' ] || [ $1 == '?' ]; then
	echo "Modifies extension of a group of files in current directory"
	echo "usage: ext-modify.sh [old extension] [new extension]"
	exit 0
fi
OLDEXT=$1
NEWEXT=$2
echo "This script modifies the extension of a group of existing files."
if [ -z "$1" ]; then
	echo "Enter the current extension without a period:"
	read OLDEXT
	echo "Enter the new extension without a period:"
	read NEWEXT
else
	echo "Using arguments..."
fi
if test -n "$(find -name '*.'$OLDEXT -print -quit)" 
then
	echo "Found existing file extension."
else
	echo "ERROR: There are no existing files with the extension you specified."
	exit 0
fi
for file in *.$OLDEXT
do
	mv -v "$file" "${file%.$OLDEXT}.$NEWEXT"
done
count=(*.$NEWEXT)
if [ ${#count[@]} == 1 ]; then
	echo "${#count[@]}" "file had its extension modified."
else
	echo "${#count[@]}" "files had their extension modified."
fi
exit 0