rename batch files, and add leading zero's before underscore

Question

I have multiple files Batch1_00000001 till Batch9999_00000001 containing the following filenames:

Batch1_00000001.pdf
Batch10_00000001.pdf
Batch100_00000001.pdf
Batch1000_00000001.pdf

First of all I want to remove the word Batch and add the letter b to the front of the filenames. After that I want to add up to three leading zero's at the start. So that b1_00000001.pdf becomes b0001_00000001.pdf like:

b0001_00000001.pdf
b0010_00000001.pdf
b0100_00000001.pdf
b1000_00000001.pdf

Does anyone have a solution to break it all down, or make a single regex rename solution? Thanks in advance!

Answer 1

You can try:

#!/bin/bash
cd /directory_contain_files
for file in *.pdf; do
        index=$(echo $file | cut -d'_' -f1 | grep -o "[0-9]*")
        if [[ $index -lt 10 ]]; then
                index="000$index"
        elif [[ $index -lt 100 ]]; then
                index="00$index"
        elif [[ $index -lt 1000 ]]; then
                index="0$index"
        fi
        mv $file b${index}_00000001.pdf
done