Need help reprogramming a short batch program to macOS bash - bash

Question

I've written a batch program (long time ago now) to backup my data from one external drive to another. It scans the drive, makes a directory file of all the folders in it, and counts the number of lines (and thus folders). From there it reads from that file, one line at a time, and copies the contents of each folder in the list in the directory file to the other drive, only copying what was new or modified from the last time it copied, and if something was on the backup drive, that had been deleted from the source drive, it left it there. It just kept adding, not deleting. This was intentional, don't worry.
Here is the script:
#echo off
set /p Drive=The Archive Drive Letter:
cls
set /p Drive2=The Archive II Drive Letter:
dir %Drive%:\ /B >directory
#setlocal enableextensions enabledelayedexpansion
set lines=0
:the
set location=directory
set /a "lines = lines + 1"
set curr=1
for /F "delims=" %%a in ('type %location%') do (
for %%b in (!lines!) do (
if !curr!==%%b set foldername=%%a
)
set /a "curr = curr + 1"
)
xcopy "%drive%:\%foldername%" "%Drive2%:\THE ARCHIVE Backup\%foldername%\" /S /M /Y
timeout -t 2
goto :the
endlocal
I need help with making an identical program to run under MacOS bash.
I have experimented with the equivalent commands and researched how things are done in bash, but I have very limited experience with using MacOS.
I appreciate that some things are done differently under bash, such as drive naming. In my batch script above, I have a call for a user variable to confirm the drive letters, but that was only a failsafe in case drive letters change (as they do). However under MacOS drives are called via names, which I won't be changing so that part of the code I'm happy to remove.
In my specific case,
The source drive is located at "/Volumes/The ARCHIVE"
The destination drive is located at "/Volumes/The ARCHIVE II"
Any help is much appreciated, and I'm happy to take on any ideas that may improve my somewhat messy approach to things.
Thanks!
Edit:
I ran the command (with the -n switch), and after having some difficulties with the “bad interpreter” error, which I’ve solved, I’m returned a list of all my files on the source drive. I assume this will return to none after one backup, and only subsequent changes on the source drive??
Also, I’m returned a line that says “total size is 528045001932” I assume this is in bytes, and therefore when converted to gigabytes comes to 528GB, or 491GB (depends on 1024 vs 1000 bytes per kilobyte). Only thing is, my total amount of data on the source drive is more than that. Does that mean that rsync has missed some data, or has it skipped some of it because it found matches on the destination drive?

Answer 1

Just use rsync. You could set a cron job to run a bash script that rsync's one directory to another.
just save the following as something like copier.sh
#!/bin/bash
rsync -rv /Volumes/ARCH /Volumes/ARCH2
then add the file to crontab.
Check the man pages for rsync and crontab if you need help
EDIT:
I forget MacOS prefers you to use launchd now. You should read up on how to use launchd but I'll give you an example that may or may not work.
Create a plist file called something like com.directoryCopier.plist and place it in the /Library/LaunchDaemons directory. The file should look something like this:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Label</key>
<string>com.directoryCopier</string>
<key>ProgramArguments</key>
<array>
<string>/Users/Path/To/copier.sh</string>
</array>
<key>StartInterval</key>
<integer>86400</integer>
<key>StandardErrorPath</key>
<string>/tmp/copier.err</string>
<key>StandardOutPath</key>
<string>/tmp/copier.out</string>
<key>RunAtLoad</key>
<true/>
</dict>
</plist>
Start the service by rebooting or by entering the command
sudo launchctl load /Library/LaunchDaemons/com.directoryCopier.plist
You can read more here
https://developer.apple.com/library/content/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/CreatingLaunchdJobs.html
I probably left some stuff out but I'm sure someone will correct me.
Good luck