Rename a bunch of files by zero padding

pad-rename.sh

N=100

# create
for ((i = 1; i <= N; i++)); do 
  touch e-$i.csv
done

# rename
# note %04d - pad to 4 zeros
for ((i = 1; i <= N; i++)); do 
  mv e-$i.csv $(printf e-%04d.csv $i)
done