pad filenames left with zeros

pad_filenames_zeros

→ ls
file1.txt   file14.txt  file19.txt  file23.txt  file28.txt  file32.txt  file37.txt  file41.txt  file46.txt  file50.txt  file55.txt  file6.txt
file10.txt  file15.txt  file2.txt   file24.txt  file29.txt  file33.txt  file38.txt  file42.txt  file47.txt  file51.txt  file56.txt  file7.txt
file11.txt  file16.txt  file20.txt  file25.txt  file3.txt   file34.txt  file39.txt  file43.txt  file48.txt  file52.txt  file57.txt  file8.txt
file12.txt  file17.txt  file21.txt  file26.txt  file30.txt  file35.txt  file4.txt   file44.txt  file49.txt  file53.txt  file58.txt  file9.txt
file13.txt  file18.txt  file22.txt  file27.txt  file31.txt  file36.txt  file40.txt  file45.txt  file5.txt   file54.txt  file59.txt
~/tmp/files  2014-11-26 12:09:55
→ for f in $(ls); do newnum=$(ruby -e "/file(?<num>\d+).txt/ =~ '$f'; puts num.rjust(2,'0')"); mv $f file$newnum.txt; done
mv: ‘file10.txt’ and ‘file10.txt’ are the same file
mv: ‘file11.txt’ and ‘file11.txt’ are the same file
mv: ‘file12.txt’ and ‘file12.txt’ are the same file
mv: ‘file13.txt’ and ‘file13.txt’ are the same file
mv: ‘file14.txt’ and ‘file14.txt’ are the same file
mv: ‘file15.txt’ and ‘file15.txt’ are the same file
mv: ‘file16.txt’ and ‘file16.txt’ are the same file
mv: ‘file17.txt’ and ‘file17.txt’ are the same file
mv: ‘file18.txt’ and ‘file18.txt’ are the same file
mv: ‘file19.txt’ and ‘file19.txt’ are the same file
mv: ‘file20.txt’ and ‘file20.txt’ are the same file
mv: ‘file21.txt’ and ‘file21.txt’ are the same file
mv: ‘file22.txt’ and ‘file22.txt’ are the same file
mv: ‘file23.txt’ and ‘file23.txt’ are the same file
mv: ‘file24.txt’ and ‘file24.txt’ are the same file
mv: ‘file25.txt’ and ‘file25.txt’ are the same file
mv: ‘file26.txt’ and ‘file26.txt’ are the same file
mv: ‘file27.txt’ and ‘file27.txt’ are the same file
mv: ‘file28.txt’ and ‘file28.txt’ are the same file
mv: ‘file29.txt’ and ‘file29.txt’ are the same file
mv: ‘file30.txt’ and ‘file30.txt’ are the same file
mv: ‘file31.txt’ and ‘file31.txt’ are the same file
mv: ‘file32.txt’ and ‘file32.txt’ are the same file
mv: ‘file33.txt’ and ‘file33.txt’ are the same file
mv: ‘file34.txt’ and ‘file34.txt’ are the same file
mv: ‘file35.txt’ and ‘file35.txt’ are the same file
mv: ‘file36.txt’ and ‘file36.txt’ are the same file
mv: ‘file37.txt’ and ‘file37.txt’ are the same file
mv: ‘file38.txt’ and ‘file38.txt’ are the same file
mv: ‘file39.txt’ and ‘file39.txt’ are the same file
mv: ‘file40.txt’ and ‘file40.txt’ are the same file
mv: ‘file41.txt’ and ‘file41.txt’ are the same file
mv: ‘file42.txt’ and ‘file42.txt’ are the same file
mv: ‘file43.txt’ and ‘file43.txt’ are the same file
mv: ‘file44.txt’ and ‘file44.txt’ are the same file
mv: ‘file45.txt’ and ‘file45.txt’ are the same file
mv: ‘file46.txt’ and ‘file46.txt’ are the same file
mv: ‘file47.txt’ and ‘file47.txt’ are the same file
mv: ‘file48.txt’ and ‘file48.txt’ are the same file
mv: ‘file49.txt’ and ‘file49.txt’ are the same file
mv: ‘file50.txt’ and ‘file50.txt’ are the same file
mv: ‘file51.txt’ and ‘file51.txt’ are the same file
mv: ‘file52.txt’ and ‘file52.txt’ are the same file
mv: ‘file53.txt’ and ‘file53.txt’ are the same file
mv: ‘file54.txt’ and ‘file54.txt’ are the same file
mv: ‘file55.txt’ and ‘file55.txt’ are the same file
mv: ‘file56.txt’ and ‘file56.txt’ are the same file
mv: ‘file57.txt’ and ‘file57.txt’ are the same file
mv: ‘file58.txt’ and ‘file58.txt’ are the same file
mv: ‘file59.txt’ and ‘file59.txt’ are the same file
~/tmp/files  2014-11-26 12:10:04
→ ls
file01.txt  file06.txt  file11.txt  file16.txt  file21.txt  file26.txt  file31.txt  file36.txt  file41.txt  file46.txt  file51.txt  file56.txt
file02.txt  file07.txt  file12.txt  file17.txt  file22.txt  file27.txt  file32.txt  file37.txt  file42.txt  file47.txt  file52.txt  file57.txt
file03.txt  file08.txt  file13.txt  file18.txt  file23.txt  file28.txt  file33.txt  file38.txt  file43.txt  file48.txt  file53.txt  file58.txt
file04.txt  file09.txt  file14.txt  file19.txt  file24.txt  file29.txt  file34.txt  file39.txt  file44.txt  file49.txt  file54.txt  file59.txt
file05.txt  file10.txt  file15.txt  file20.txt  file25.txt  file30.txt  file35.txt  file40.txt  file45.txt  file50.txt  file55.txt
~/tmp/files  2014-11-26 12:10:07
→