What does the below regular expression means?

Question

Can anyone explain what the below regex means

"^[0-9]{1,20}$"

Answer 1

Basically it says that the string to check is a number of up to 20 characters.

^ => Start of string

[0-9] => matches numbers

{1,20} => 1 to 20 repetitions of the condition left to it

$ => end of string