Shell Programming and Scripting

I am new to bash. But I need read a snippet of script. I saw some expression like this below. I can figure it out by coding a snippet.

But I fount that the curly bracket("{}") have so much use. Could you please give some tutorial about the curly bracket, or some sort of summary about it?

I will really appreciate it.
Thank you in advance.

1. ${1%%[0-9]*} It means to intercept $1 from the place digits begins, and assign the non-digits to $1. If $1 starts with num then just assign null to $1

2. ${{1//[^0-9a-zA-Z_]/_} This means to replace all elements if it is not digits, alphabets or underscore with underscore.

Please use code tags as required by forum rules!

Not sure what you want to know. Your interpretations are correct. All ${...} are parameter expansions or array references, see there in man bash. Other use of {...} is concatenating a command list, and creating sequences in brace expansions. Again, man bash will help.

Please use google before asking such easy questions here.