mv 1.txt.txt 01.txt
mv 1.xls 01.xls
mv 2.txt 02.txt
mv 2.xls 02.xls
mv 3.txt 03.txt
mv 3.xls 03.xls
mv 4.txt 04.txt
mv 4.xls 04.xls
mv 5.txt 05.txt
mv 6.txt 06.txt
mv 6.xls 06.xls
mv 7.txt 07.txt
mv 7.xls 07.xls
mv 8.txt 08.txt
mv 8.xls 08.xls