variable-interpolation.md

Variable interpolation

A value may reference another variable with ${NAME}. References are resolved when you read the value with get(), not when the file is loaded.

SITE_URL = http://lvh.me
PAGE_URL = ${SITE_URL}/page

DotENV::get('PAGE_URL'); // "http://lvh.me/page"

Multiple references on one line

Any number of references may appear in a single value:

HOST = localhost
PORT = 8080
ADDR = ${HOST}:${PORT}

DotENV::get('ADDR'); // "localhost:8080"

Nested references

A referenced value may itself contain references; they are resolved recursively:

A = root
B = ${A}/b
C = ${B}/c

DotENV::get('C'); // "root/b/c"

Resolution source

${NAME} is resolved with the same lookup that get() uses ($_ENV → $_SERVER → getenv()), so a reference can point at a real environment variable, not just another line in the same file.

How the referenced value is inserted

A reference is replaced with the string cast of the referenced value, then the whole surrounding value is coerced as usual. So referencing a coerced type behaves like PHP's (string) cast:

NAME value	${NAME} inserts	WRAP=${NAME} becomes
"text"	text	"text"
13	13	13 (int)
true	1	1 (int)
false	(empty)	""
null	(empty)	""

A non-scalar referenced value (an array or object loaded from a .env.php file) inserts an empty string.

Missing references

A reference to an undefined name resolves to an empty string:

VALUE = ${DOES_NOT_EXIST}suffix

DotENV::get('VALUE'); // "suffix"

Circular references

A reference back to a name that is still being resolved (a self-reference or a cycle) is replaced with an empty string instead of recursing forever. Any literal text around the reference is kept:

A = ${A}
B = ${C}
C = ${B}
D = ${D}-tail

DotENV::get('A'); // ""
DotENV::get('B'); // ""
DotENV::get('C'); // ""
DotENV::get('D'); // "-tail"   (the cyclic ${D} is dropped, "-tail" remains)