Accessing environment variables within a Docker container using shell commands

To access environment variables within a Docker container using shell commands, you can follow these steps:

Set Environment Variables: When you run a Docker container, you can set environment variables using the -e or --env flag. For example:

docker run -e MY_VARIABLE=example_value -it my_image

Access Environment Variables: Once you’re inside the Docker container, you can use shell commands to access these variables. Here’s how you can do it with different shells:

Bash / Sh: Use the echo command to display the value of an environment variable.

echo $MY_VARIABLE

Fish: Use the echo command as well, but access the variable slightly differently.

echo $MY_VARIABLE

List All Environment Variables: If you want to see all the environment variables available in the container, use the env or printenv command.

env
# or
printenv

Use Environment Variables in Scripts: You can also use environment variables within scripts that run inside the container. For example, in a bash script:

#!/bin/bash
echo "The value of MY_VARIABLE is: $MY_VARIABLE"

#!/bin/bash
echo "The value of MY_VARIABLE is: $MY_VARIABLE"

Exporting Variables: If you need to set a new environment variable inside the container for use by subsequent commands, use the export command.

export NEW_VARIABLE="new_value"

Pass Environment Variables from a File: You can also pass environment variables from a file using the –env-file flag when running the container.

docker run --env-file my_env_file.txt -it my_image