Using regular expressions(REs) is just like using REs in other common languages (C#, java, php, python...). REs in bash has two syntaxes,
extended, which are defined in IEEE POSIX standard. The basic syntax is the default mode in bash.
Commonly used metacharacters used in bash are
bracket expression. Used to match a selection of characters.
dot sign matches any single character.
*, +, ?
matches a preceding item zero or more times, one or more times, zero or one time, resp.
matches the empty string in the start, or the end of a line.