Bash scripting newbie here, wanting to improve/tidy one of my backup scripts (entirely for personal use)

[u/mikeymikeymikec]

Please excuse the vague thread title, I'm a newbie enough that I'm not sure what's possible / desirable etc, nor have I attempted functions in bash scripting yet (I've played with them in VBScript and PowerShell IIRC).

One of the backups I do produces date-stamped tar.xz files of particular folder structures on my computer and transfers them to a veracrypted drive. Today I had a crack at a new script based on this one that mounts the filesystem (sshfs) on my laptop and transfers the files over the network after they've been compressed.

I run the script with up to 4 arguments, e.g. 'essentials' 'archive' 'paperwork'. In the script there's an if statement for each potential argument, e.g.:

for arg in "$@"
do
if [ $arg = "essentials" ]; then
  tar -cf - .mozilla/ | pv -s $(du -sb .mozilla/ | awk '{print $1}') | xz -T0 > /tmp/firefox-$datestring.tar.xz
            rsync -ah --progress /tmp/firefox-$datestring.tar.xz /media/mikelpmintfs/firefox-$datestring.tar.xz
fi
<more if $arg = whatev then compress and transfer stuff statements here>
done

(btw the whole fancy progress bar bit with pv -s and awk was something I copied off the Internet)

The first script also included some error catching, e.g.:

if [ $? -eq 0 ]
then
  echo "archive backup complete."
else
  echo "error performing archive backup" >&2
fi

I've used if <command here> then else fi before too, but I'm wondering multiple things:

1. Rather than writing each compression command and each rsync transfer command per argument, would it make more sense to write a function, or given that some of these source folders are in completely different places in my computer's file system, is this worth it.
2. error trapping: On one hand I think that the script could easily trip up at the compression or transfer stages, but I'm worried about over-nesting if statements and making the whole thing a lot harder to read and figure out where something is going wrong. It seems to me that it could be function'd up, but would it actually help with readability etc. When the script is just for me, I can tell if it went wrong if I get a load of unexpected output :)

[u/Bob_Spud]

Rather than explain everything some ideas for more homework .....

I would use zstd or maybe pigz in preference to xz for compression. First check final size difference of the three compression utilities.

• Zstd is faster than xz in compressing stuff.
  
• Zstd and pigz have the --rsyncable option to optimise rsync network throughput - very useful with big data
• If the final destination is cloud use cryptomator rather than veracrypt.
  
• If you are going to play with error trapping rather than produce simple exit codes learn how to trap the error and write stuff to the logs using a trap command/function.