ref
-- https://docstore.mik.ua/orelly/unix/upt/ch08_19.htm

` 		backquotes 		Command substitution
" 		double quote		Weak quotes
' 		single quote		Strong quotes
\ 		back slash		Single-character quote
$ var 		dolar sign		Variable
${var-default}  			If var not set, use default .
? 					Match one character. 	
* 					Match zero or more characters.