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

Set environment variables with export and confirm their values.

sample_env_setup.sh

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

Run the following command:

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.

sample_export_later.sh

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

The following example demonstrates this:

bash export_later.sh
VERSION: 1.2.3

Check common environment variables.

sample_show_env.sh

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

Run the following command:

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.

sample_path_add.sh

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

Run the following command:

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

Common Mistake 1: export in a child shell does not propagate to the parent

Variables exported in a child process (subshell or script) are not visible in the parent shell that called it.

bash set_var.sh
echo $MY_VAR
（empty — the variable was set only inside the script）

Use source (or .) to run the script in the current shell so the variable is available after.

source set_var.sh
echo $MY_VAR
hello

Common Mistake 2: Overwriting PATH entirely makes standard commands unavailable

Setting PATH without preserving its existing value removes all default command directories.

export PATH="/home/okabe/bin"
ls
bash: ls: command not found

Prepend the new directory while keeping the existing value.

export PATH="/home/okabe/bin:$PATH"

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.