# Define Environment Variables for a Container
LLMS index: [llms.txt](/llms.txt)
---
This page shows how to define environment variables for a container
in a Kubernetes Pod.
## Before you begin
You need to have a Kubernetes cluster, and the kubectl command-line tool must
be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a
cluster, you can create one by using
minikube
or you can use one of these Kubernetes playgrounds:
## Define an environment variable for a container
When you create a Pod, you can set environment variables for the containers
that run in the Pod. To set environment variables, include the `env` or
`envFrom` field in the configuration file.
The `env` and `envFrom` fields have different effects.
`env`
: allows you to set environment variables for a container, specifying a value directly for each variable that you name.
`envFrom`
: allows you to set environment variables for a container by referencing either a ConfigMap or a Secret.
When you use `envFrom`, all the key-value pairs in the referenced ConfigMap or Secret
are set as environment variables for the container.
You can also specify a common prefix string.
You can read more about [ConfigMap](/docs/tasks/configure-pod-container/configure-pod-configmap/#configure-all-key-value-pairs-in-a-configmap-as-container-environment-variables)
and [Secret](/docs/tasks/inject-data-application/distribute-credentials-secure/#configure-all-key-value-pairs-in-a-secret-as-container-environment-variables).
This page explains how to use `env`.
In this exercise, you create a Pod that runs one container. The configuration
file for the Pod defines an environment variable with name `DEMO_GREETING` and
value `"Hello from the environment"`. Here is the configuration manifest for the
Pod:
apiVersion: v1
kind: Pod
metadata:
name: envar-demo
labels:
purpose: demonstrate-envars
spec:
containers:
- name: envar-demo-container
image: gcr.io/google-samples/hello-app:2.0
env:
- name: DEMO_GREETING
value: "Hello from the environment"
- name: DEMO_FAREWELL
value: "Such a sweet sorrow"
1. Create a Pod based on that manifest:
```shell
kubectl apply -f https://k8s.io/examples/pods/inject/envars.yaml
```
1. List the running Pods:
```shell
kubectl get pods -l purpose=demonstrate-envars
```
The output is similar to:
```
NAME READY STATUS RESTARTS AGE
envar-demo 1/1 Running 0 9s
```
1. List the Pod's container environment variables:
```shell
kubectl exec envar-demo -- printenv
```
The output is similar to this:
```
NODE_VERSION=4.4.2
EXAMPLE_SERVICE_PORT_8080_TCP_ADDR=10.3.245.237
HOSTNAME=envar-demo
...
DEMO_GREETING=Hello from the environment
DEMO_FAREWELL=Such a sweet sorrow
```
Note:
The environment variables set using the env or envFrom field
override any environment variables specified in the container image.
Note:
Environment variables may reference each other, however ordering is important.
Variables making use of others defined in the same context must come later in
the list. Similarly, avoid circular references.
## Using environment variables inside of your config
Environment variables that you define in a Pod's configuration under
`.spec.containers[*].env[*]` can be used elsewhere in the configuration, for
example in commands and arguments that you set for the Pod's containers.
In the example configuration below, the `GREETING`, `HONORIFIC`, and
`NAME` environment variables are set to `Warm greetings to`, `The Most
Honorable`, and `Kubernetes`, respectively. The environment variable
`MESSAGE` combines the set of all these environment variables and then uses it
as a CLI argument passed to the `env-print-demo` container.
Environment variable names may consist of any [printable ASCII characters](https://www.ascii-code.com/characters/printable-characters) except '='.
```yaml
apiVersion: v1
kind: Pod
metadata:
name: print-greeting
spec:
containers:
- name: env-print-demo
image: bash
env:
- name: GREETING
value: "Warm greetings to"
- name: HONORIFIC
value: "The Most Honorable"
- name: NAME
value: "Kubernetes"
- name: MESSAGE
value: "$(GREETING) $(HONORIFIC) $(NAME)"
command: ["echo"]
args: ["$(MESSAGE)"]
```
Upon creation, the command `echo Warm greetings to The Most Honorable Kubernetes` is run on the container.
## What's next
* Learn more about [environment variables](/docs/tasks/inject-data-application/environment-variable-expose-pod-information/).
* Learn about [using secrets as environment variables](/docs/concepts/configuration/secret/#using-secrets-as-environment-variables).
* See [EnvVarSource](/docs/reference/generated/kubernetes-api/v1.36/#envvarsource-v1-core).
