Help me to understand some regular expresions usage

Shell Programming and Scripting
1

Can someone explain me how those restatements are constructed

        suffix=${name#*.}
        prefix=${main%%+([0-9])}
        num=10#${num}
  1. What is the logic to use a reg-expr in variable name
  2. In first string - the '#' seems to mean 'everithing after next mached', but the '.' in reg-exp is a one character, here it seems it used litteraly. Why?
  3. I guess '%%' means return part that match next expression? Is it correct?
  4. Why the '()' used in second string? [0-9] - any digit; '+' one or more times; so, +[0-9] should return consecutive numbers from string?! What is the need in '()'
  5. How to understand third line? What is done by that whith string of digits?

Thank you

2

You don't use regular expressions in parameter expansion; you use
filename expansion (a.k.a. wildcard) patterns.

See:
POSIX shell parameter expansions