> for FILE in *.txt; do cp $FILE $FILE.bak; sed -e "s/hoge/moge/g" $FILE.bak > $FILE; done

> OLD=hoge; NEW=moge; for FILE in *$OLD; do PREFIX=`expr $FILE : '\(.*\)'$OLD`; SUFFIX=`expr $FILE : $PREFIX$OLD'\(.*\)'`; mv $PREFIX$OLD$SUFFIX $PREFIX$NEW$SUFFIX; done