= String operations

== String concatenation

String concatenation uses the `+` operator.

[source]
....
nix-repl> "Hello, " + "world!"
"Hello, world!"
....

== String interpolation

You can use the `${_variable_}` syntax to insert the value of a variable within a string.

[source]
....
nix-repl> name = "Wombat"

nix-repl> "Hi, I'm ${name}."
"Hi, I'm Wombat."
....

[IMPORTANT]
====
You cannot mix numbers and strings.
Earlier we set `a = 7`, so the following expression fails.

[source]
....
nix-repl> "My favourite number is ${a}."
error:
       … while evaluating a path segment

         at «string»:1:25:

            1| "My favourite number is ${a}."
             |                         ^

       error: cannot coerce an integer to a string
....
Nix does provide functions for converting between types; we'll see these in <<_built_in_functions>>.
====

== Useful built-in functions for strings

Nix provides some built-in functions for working with strings;
a few examples are shown below.
For more information on these and other built-in functions, see the Nix Manual
(https://nixos.org/manual/nix/stable/language/builtins).

How long is this string?

[source]
....
nix-repl> builtins.stringLength "supercalifragilisticexpialidocious"
34
....

Given a starting position and a length, extract a substring.
The first character of a string has index `0`.

[source]
....
nix-repl> builtins.substring 3 6 "hayneedlestack"
"needle"
....

Convert an expression to a string.

[source]
....
nix-repl> builtins.toString 7
"7"

nix-repl> builtins.toString (3*4 + 1)
"13"
....