nix/doc/manual/src/language/operators.md

Operators

The table below lists the operators in the Nix language, in order of precedence (from strongest to weakest binding).

Name	Syntax	Description	Associativity	Precedence
Select	e . attrpath [ or def ]	Select attribute denoted by the attribute path attrpath from set e. (An attribute path is a dot-separated list of attribute names.) If the attribute doesn’t exist, return def if provided, otherwise abort evaluation.	none	1
Application	e1 e2	Call function e1 with argument e2.	left	2
Arithmetic Negation	- e	Arithmetic negation.	none	3
Has Attribute	e ? attrpath	Test whether set e contains the attribute denoted by attrpath; return true or false.	none	4
List Concatenation	e1 ++ e2	List concatenation.	right	5
Multiplication	e1 * e2,	Arithmetic multiplication.	left	6
Division	e1 / e2	Arithmetic division.	left	6
Addition	e1 + e2	Arithmetic addition.	left	7
Subtraction	e1 - e2	Arithmetic subtraction.	left	7
String Concatenation	string1 + string2	String concatenation.	left	7
Not	! e	Boolean negation.	none	8
Update	e1 // e2	Return a set consisting of the attributes in e1 and e2 (with the latter taking precedence over the former in case of equally named attributes).	right	9
Less Than	e1 < e2,	Arithmetic/lexicographic comparison.	none	10
Less Than or Equal To	e1 <= e2	Arithmetic/lexicographic comparison.	none	10
Greater Than	e1 > e2	Arithmetic/lexicographic comparison.	none	10
Greater Than or Equal To	e1 >= e2	Arithmetic/lexicographic comparison.	none	10
Equality	e1 == e2	Equality.	none	11
Inequality	e1 != e2	Inequality.	none	11
Logical AND	e1 && e2	Logical AND.	left	12
Logical OR	e1 || e2	Logical OR.	left	13
Logical Implication	e1 -> e2	Logical implication (equivalent to !e1 || e2).	none	14