In certain contexts, expression values also serve as “truth values;” i.e.,
they determine what should happen next as the program runs. This
section describes how awk defines “true” and “false”
and how values are compared.
Truth Values: What is ``true'' and what is ``false''.
Typing and Comparison: How variables acquire types and how this
affects comparison of numbers and strings with
‘<’, etc.
Boolean Ops: Combining comparison expressions using boolean
operators ‘||’ (``or''), ‘&&’
(``and'') and ‘!’ (``not'').
Conditional Exp: Conditional expressions select between two
subexpressions under control of a third
subexpression.