Interpolation of Values

In addition to its core functionality, PlatformIO introduces support for interpolation, allowing values to incorporate format strings that reference other values from different sections.

The interpolation feature adheres to the following syntax:

  • ${<variable>}, where <variable> represents the name of a supported built-in variable (refer to the table below for details).

  • ${<section>.<option>}, with <section> denoting a value from the [<section>] group, and <option> representing the first item in the pair <option> = value.





Incorporate built-in variables using their designated names. The following variables are supported:

  • PROJECT_DIR - represents the current project directory

  • PROJECT_HASH - corresponds to the hash of the project path

  • UNIX_TIME - indicates the current Unix time, represented by 10 digits

/tmp/pio-workspaces/${PROJECT_HASH} refers to the new directory /tmp/pio-workspaces/project_name-8f66e9463d/


Embed operating system environment variable by a name

${sysenv.HOME} refers to the user home directory on Unix machine


Embed value from Section [platformio]

${platformio.packages_dir} refers to the path of packages_dir


Embed default value from Section [env]

${env.debug_build_flags} refers to the default debugging flags


Embed value from another section.

${extra.lib_deps} embeds library dependencies declared in the section named extra


Embed value from the current section without declaring a section name

${this.board} refers to the “board” value of the current section


Embed environment name of the current section. The section must start with env: prefix

${this.__env__} will embed “foo” value being declared in the “env:foo” section

  • Interpolation can span multiple levels

  • Interpolation can be applied only for the option’s value

  • Multiple interpolations are allowed

  • The Section [platformio] and Section [env] sections are reserved and could not be used as a custom section. Some good section names might be extra or custom.


If you need to share common configuration options between build environments, please take a look at “Global scope” in Section [env] or extends option which allows extending of other sections.


; COMMON options
; Each "[env:***]" extends this "[env]" by default
framework = arduino
build_flags = -D VERSION=1.2.3

; CUSTOM options
; You need manually inject these options into a section
; using ${extra.<name_of_option>} (see below)
lib_deps_builtin =
lib_deps_external =

platform = atmelavr
board = uno
lib_deps =
platform_packages =
test_speed = 9600
test_testing_command =

platform = espressif32
board = esp32dev
build_flags = ${env.build_flags} -Wall
lib_deps =
  knolleary/PubSubClient @ ~2.6
  paulstoffregen/OneWire @ ^2.3.5

; Keep sensitive data in environment variables
; Unix
; export WIFI_SSID='\"my\ ssid\ name\"'
; export WIFI_PASS='\"my\ password\"'
; Windows
; set WIFI_SSID='"my ssid name"'
; set WIFI_PASS='"my password"'


Be careful with special characters in system environment variables on Unix systems, especially when they are used as the value for preprocessor directives. Symbols like $, &, ~, etc must be explicitly escaped, for example:

export WIFI_PASS='\"my\~p\&a\\\$\$\$\$word\"'