[SOLVED] Stripping the leading zeros but leave a single 0

Issue

So let me start of by saying that I'm new to bash so I would appreciate a simple explanation on the answers you give.

I've got the following block of code:

name="Chapter 0000 (sub s2).cbz "

s=$(echo $name | grep -Eo '[0-9]+([.][0-9]+)?' | tr '\n' ' ' | sed 's/^0*//')

echo $s

readarray -d " " -t myarr <<< "$s"

if [[ $(echo "${myarr[0]} < 100 && ${myarr[0]} >= 10" | bc) -ne 0 ]]; then
    myarr[0]="0${myarr[0]}"
elif [[ $(echo "${myarr[0]} < 10" | bc) -ne 0 ]]; then
    myarr[0]="00${myarr[0]}"
fi

newName="Chapter ${myarr[0]}.cbz"

echo $newName

which (in this case) would end up spitting out:

 2
(standard_in) 1: syntax error
(standard_in) 1: syntax error
Chapter .cbz

(I'm fairly certain that the syntax errors are because ${myarr[0]} is null when doing the comparisons)

This is not the output I want. I want the code to strip leading 0's but leave a single 0 if its all 0.

So the code to really change would be sed 's/^0*//') but I'm not sure how to change it.

(expected outputs:

              in   --->   out
1) chapter 8.cbz   ---> Chapter 008.cbz
2) chapter 1.3.cbz   ---> Chapter 001.3.cbz
3) _23 (sec 2).cbz   ---> Chapter 023.cbz
4) chapter 00009.cbz   ---> Chapter 009.cbz
5) chap 0000112.5.cbz   ---> Chapter 112.5.cbz
6) Chapter 0000 (sub s2).cbz   ---> Chapter 000.cbz

so far the code I got works for 1- 3 but not the leading 0 cases (4-6))

Solution

In pure bash:

#!/bin/bash

for name in \
    'chapter 8.cbz' \
    'chapter 1.3.cbz' \
    '_23 (sec 2).cbz' \
    'chapter 00009.cbz' \
    'chap 0000112.5.cbz' \
    'Chapter 0000 (sub s2).cbz' \
    '_23.2 (sec 2).cbz'
do

##### The relevant part #####

[[ $name =~ ^[^0-9]*([0-9]+)([0-9.]*)[^.]*(\..*)$ ]]

chapter=$(( 10#${BASH_REMATCH[1]} ))
suffix="${BASH_REMATCH[2]}${BASH_REMATCH[3]}"

newName=$(printf 'Chapter %03d%s' "$chapter" "$suffix")

#############################

echo "$newName"

done

Chapter 008.cbz
Chapter 001.3.cbz
Chapter 023.cbz
Chapter 009.cbz
Chapter 112.5.cbz
Chapter 000.cbz
Chapter 023.2.cbz

notes:

• [[ =~ ]] is the way to use an ERE regex in bash. The one that I wrote has two capture groups: one for capturing the first appearing sequence of digits (which should be the chapter number), and one for capturing all the characters that appear after the first dot (included).
• $(( 10#... )) converts a zero prefixed decimal to a normal decimal. This is needed because a number that starts with 0 would mean that's an octal instead of a decimal.
• printf '%03d' converts a number to a decimal of at least 3 digits, padding the left with zeros when it's not the case.

Answered By - Fravadona

Answer Checked By - Candace Johnson (WPSolving Volunteer)