Operators

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

Name	Syntax	Associativity	Description	Precedence
Select	e `.` attrpath [ `or` def ]	none	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.	1
Application	e1 e2	left	Call function e1 with argument e2.	2
Arithmetic Negation	`-` e	none	Arithmetic negation.	3
Has Attribute	e `?` attrpath	none	Test whether set e contains the attribute denoted by attrpath; return `true` or `false`.	4
List Concatenation	e1 `++` e2	right	List concatenation.	5
Multiplication	e1 `*` e2,	left	Arithmetic multiplication.	6
Division	e1 `/` e2	left	Arithmetic division.	6
Addition	e1 `+` e2	left	Arithmetic addition.	7
Subtraction	e1 `-` e2	left	Arithmetic subtraction.	7
String Concatenation	string1 `+` string2	left	String concatenation.	7
Not	`!` e	none	Boolean negation.	8
Update	e1 `//` e2	right	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).	9
Less Than	e1 `<` e2,	none	Arithmetic comparison.	10
Less Than or Equal To	e1 `<=` e2	none	Arithmetic comparison.	10
Greater Than	e1 `>` e2	none	Arithmetic comparison.	10
Greater Than or Equal To	e1 `>=` e2	none	Arithmetic comparison.	10
Equality	e1 `==` e2	none	Equality.	11
Inequality	e1 `!=` e2	none	Inequality.	11
Logical AND	e1 `&&` e2	left	Logical AND.	12
Logical OR	e1 `\|\|` e2	left	Logical OR.	13
Logical Implication	e1 `->` e2	none	Logical implication (equivalent to `!e1 \|\
e2`).	14