export / env / printenv

Export a variable as an environment variable.

export VARNAME=value
export VARNAME   # Export an already-defined variable

List all environment variables.

env
printenv

Display a specific environment variable.

printenv VARNAME
echo $VARNAME

Set an environment variable only for a single command.

VARNAME=value command

Command / Variable	Description
export VAR=value	Defines a variable and sets it as an environment variable.
export VAR	Exports an existing shell variable so child processes can access it.
env	Lists all current environment variables.
printenv	Lists environment variables (similar to env).
printenv VAR	Displays the value of the specified environment variable only.
unset VAR	Removes an environment variable.
$PATH	A colon-separated list of directories searched for commands.
$HOME	The path to the current user's home directory.
$USER	The name of the currently logged-in user.
$SHELL	The path to the current shell.
$PWD	The path to the current working directory.
$LANG	The current locale setting.

Set environment variables with export and confirm their values.

env_setup.sh

export APP_ENV=production
export DB_HOST=localhost
echo "APP_ENV: $APP_ENV"
echo "DB_HOST: $DB_HOST"

bash env_setup.sh
APP_ENV: production
DB_HOST: localhost

You can also export an existing shell variable as an environment variable after the fact.

export_later.sh

VERSION="1.2.3"
export VERSION
echo "VERSION: $VERSION"

bash export_later.sh
VERSION: 1.2.3

Check common environment variables.

show_env.sh

echo "User: $USER"
echo "Home: $HOME"
echo "Shell: $SHELL"
echo "Current dir: $PWD"

bash show_env.sh
User: alice
Home: /home/alice
Shell: /bin/bash
Current dir: /home/alice/project

Add a new directory to $PATH. The convention is to prepend it while keeping the existing value intact.

path_add.sh

export PATH="$HOME/bin:$PATH"
echo "First entry in PATH: $(echo $PATH | cut -d: -f1)"

bash path_add.sh
First entry in PATH: /home/alice/bin

Set an environment variable only for a single command. It does not affect the rest of the script.

LANG=C ls --help 2>&1 | head -1
Usage: ls [OPTION]... [FILE]...

Use printenv to display the value of a specific environment variable.

printenv HOME
/home/alice
printenv SHELL
/bin/bash

Shell variables are only available within the current shell, but once you export them, they are passed to child processes (subshells and external commands). By writing export statements in a configuration file (such as ~/.bashrc or ~/.bash_profile), environment variables are set automatically every time a new shell starts.

When adding to '$PATH', the convention is '$ export PATH="$HOME/bin:$PATH"' — prepend the new directory while preserving the existing value. Overwriting $PATH entirely will make standard commands unavailable.

For the basics of defining and referencing variables, see Defining and Referencing Variables.