Environment Variables

Overview

In this sample application, the POSIX setenv(), function is used to populate several environment variables in C. Then, all environment variables are then printed.

If the user sets a new value for the ALERT environment variable, it is printed to standard output, and then cleared via unsetenv().

Building and Running

This project outputs to the console. It can be built and executed on QEMU as follows:

west build -b qemu_riscv32 samples/posix/env
west build -t run

Sample Output

The program below shows sample output for a specific Zephyr build.

BOARD=qemu_riscv32
BUILD_VERSION=zephyr-v3.5.0-5372-g3a46f2d052c7
ALERT=

Setting Environment Variables

The shell command below shows how to create a new environment variable or update the value associated with an existing environment variable.

The C code that is part of this sample application displays the value associated with the ALERT environment variable and then immediately unsets it.

uart:~$ posix env set ALERT="Happy Friday!"
uart:~$ ALERT="Happy Friday!"
uart:~$ posix env set HOME="127.0.0.1"
uart:~$

Getting Environment Variables

The shell command below may be used to display the value associated with one environment variable.

uart:~$ posix env get BOARD
qemu_riscv32

The shell command below may be used to display all environment variables and their associated values.

uart:~$ posix env get
BOARD=qemu_riscv32
BUILD_VERSION=zephyr-v3.5.0-5372-g3a46f2d052c7
ALERT=

Unsetting Environment Variables

The shell command below may be used to unset environment variables.

uart:~$ posix env unset BOARD