How to append the date to a string in bash

Question

I have a script that backups my Raspberry Pi

sudo dd bs=1M if=/dev/sda1 of=/home/pi/backup.img
zip -r /home/pi/backup/backup.zip /home/pi/backup.img
cp backup.zip ~/backup

I want to know how I can append the date to the backup.zip file, generated by the second line.

Any tips?

Solution

You can use command substitution to accomplish this.
You might also want to familiarize yourself with the date components:

# Save the file name in a variable so we don't repeat ourselves
outfile="/home/pi/backup/backup.zip.$(date +%Y%m%d)"

sudo dd bs=1M if=/dev/sda1 of=/home/pi/backup.img
zip -r "${outfile}" /home/pi/backup.img
cp "${outfile}" ~/backup

The magic here is the $(date +%Y%m%d). This runs date +%Y%m%d and captures the output which will be the current date in YYYYMMDD format.