hello, may i know how can i find and change string in multiple file...i had refer some of the post here .. but found that all is about find and change string in a file only..let say i want to change all occurences of the string 'hei' to 'hello' in only the file with extension .txt....how i can do that.....thanks in advance...

#/bin/ksh
for file in `find . -name '*.txt' -type f -print` ; do
echo $file
sed -e 's/hei/hello/' $file > $file.tmp
mv $file.tmp $file
done