I came to this thread hoping someone wrote exactly what you did, otherwise I was going to do it myself. Thanks

For others not aware of this functionality, it is a well documented and old bash feature:

https://tldp.org/LDP/Bash-Beginners-Guide/html/sect_03_04.ht...

If you want to go deeper into the weeds, the parameter substitution bits are also very useful:

https://www.tldp.org/LDP/abs/html/parameter-substitution.htm...