| Basic values |
|
"Hello world" |
A string |
"${pkgs.bash}/bin/sh" |
A string containing an expression (expands to "/nix/store/hash-bash-version/bin/sh") |
true, false |
Booleans |
123 |
An integer |
./foo.png |
A path (relative to the containing Nix expression) |
| Compound values |
|
{ x = 1; y = 2; } |
A set with attributes named x and y |
{ foo.bar = 1; } |
A nested set, equivalent to { foo = { bar = 1; }; } |
rec { x = "foo"; y = x + "bar"; } |
A recursive set, equivalent to { x = "foo"; y = "foobar"; } |
[ "foo" "bar" ] |
A list with two elements |
| Operators |
|
"foo" + "bar" |
String concatenation |
1 + 2 |
Integer addition |
"foo" == "f" + "oo" |
Equality test (evaluates to true) |
"foo" != "bar" |
Inequality test (evaluates to true) |
!true |
Boolean negation |
{ x = 1; y = 2; }.x |
Attribute selection (evaluates to 1) |
{ x = 1; y = 2; }.z or 3 |
Attribute selection with default (evaluates to 3) |
{ x = 1; y = 2; } // { z = 3; } |
Merge two sets (attributes in the right-hand set taking precedence) |
| Control structures |
|
if 1 + 1 == 2 then "yes!" else "no!" |
Conditional expression |
assert 1 + 1 == 2; "yes!" |
Assertion check (evaluates to "yes!"). See for using assertions in modules |
let x = "foo"; y = "bar"; in x + y |
Variable definition |
with pkgs.lib; head [ 1 2 3 ] |
Add all attributes from the given set to the scope (evaluates to 1) |
| Functions (lambdas) |
|
x: x + 1 |
A function that expects an integer and returns it increased by 1 |
(x: x + 1) 100 |
A function call (evaluates to 101) |
let inc = x: x + 1; in inc (inc (inc 100)) |
A function bound to a variable and subsequently called by name (evaluates to 103) |
{ x, y }: x + y |
A function that expects a set with required attributes x and y and concatenates them |
{ x, y ? "bar" }: x + y |
A function that expects a set with required attribute x and optional y, using "bar" as default value for y |
{ x, y, ... }: x + y |
A function that expects a set with required attributes x and y and ignores any other attributes |
{ x, y } @ args: x + y |
A function that expects a set with required attributes x and y, and binds the whole set to args |
| Built-in functions |
|
import ./foo.nix |
Load and return Nix expression in given file |
map (x: x + x) [ 1 2 3 ] |
Apply a function to every element of a list (evaluates to [ 2 4 6 ]) |
