The constructs are compound commands and expressions.
A compound command is a comma-separated list of commands enclosed in square pairs: [command1, ..., commandN].
An expression is a set of operands connected by operators according to well-defined rules. The operands are: constants, variables and expressions in round brackets (). The operators are: arithmetic, comparison and logic.
- () (parentheses)
-  (square brackets)
- , (comma)