Linux CLI 23 🐧 printenv and export commands - KandZ

Environment variables are key-value pairs that the shell and its child processes use to store information — your username, home directory, default editor, and much more. The printenv and export commands let you view and set these variables.

What Are Environment Variables?

Environment variables are dynamic values that affect how processes run.

Variable	Description
`HOME`	User’s home directory
`USER`	Current username
`PATH`	Directories the shell searches for commands
`PWD`	Present working directory
`LANG`	Default language setting
`HOSTNAME`	Name of the computer
`DISPLAY`	X display (`:0` = first display)
`SHELL`	Current shell program
`EDITOR`	Default text editor
`TERM`	Terminal type

Key point: Environment variables are inherited by child processes — that’s why they’re called “environment.”

Viewing Variables — `printenv`

printenv USER
printenv DISPLAY
printenv LANG
printenv PATH
printenv SHELL
printenv PWD

Command	Description
`printenv`	Show all environment variables
`printenv USER`	Show a specific variable
`printenv DISPLAY`	Show X display
`printenv PATH`	Show command search path

Examples

Show all variables:

$ printenv
SHELL=/bin/bash
USER=kronos
HOME=/home/kronos
PATH=/usr/local/bin:/usr/bin:/bin
PWD=/home/kronos
LANG=en_US.UTF-8
HOSTNAME=olympos
DISPLAY=:0
TERM=xterm-256color
...

Specific variables:

$ printenv USER
kronos

$ printenv HOME
/home/kronos

$ printenv PATH
/usr/local/bin:/usr/bin:/bin

$ printenv SHELL
/bin/bash

$ printenv PWD
/home/kronos

$ printenv DISPLAY
:0

$ printenv LANG
en_US.UTF-8

$ printenv HOSTNAME
olympos

The `echo $VAR` Alternative

You can also view a variable with echo:

$ echo $USER
kronos

$ echo $HOME
/home/kronos

$ echo $PATH
/usr/local/bin:/usr/bin:/bin

$ echo $USER $HOME
kronos /home/kronos

$ echo "User: $USER, Home: $HOME"
User: kronos, Home: /home/kronos

echo vs printenv:

Aspect	`echo $VAR`	`printenv VAR`
Speed	Faster	Slightly slower
Formatting	Can mix with text	Prints raw value
Exit code	Always 0	Non-zero if not found
Use case	In scripts	Checking if variable exists

Best practice:

# For display — either works
echo $USER
printenv USER

# For scripting — use printenv to check existence
if printenv MY_VAR > /dev/null; then
    echo "MY_VAR is set"
fi

Common Environment Variables

Variable	Purpose	Example Value
`HOME`	Home directory	`/home/kronos`
`USER`	Username	`kronos`
`PATH`	Command search path	`/usr/bin:/bin`
`PWD`	Present working directory	`/home/kronos`
`LANG`	Language/locale	`en_US.UTF-8`
`HOSTNAME`	Machine name	`olympos`
`DISPLAY`	X display	`:0`
`SHELL`	Current shell	`/bin/bash`
`EDITOR`	Default text editor	`vim` or `nano`
`TERM`	Terminal type	`xterm-256color`
`PS1`	Shell prompt format	`\u@\h:\w\$`
`OLDPWD`	Previous directory	`/var/log`
`LOGNAME`	Login name	`kronos`
`UID`	User ID	`1000`

Setting Variables — `export`

export test="kronos"
echo $test
printenv test

Command	Description
`export VAR=value`	Set and export a variable
`export VAR`	Mark existing variable for export
`export -p`	List all exported variables
`export -f func`	Export a function
`export -n VAR`	Remove export flag

Temporary Variables

Local variable (not exported):

$ test="kronos"
$ echo $test
kronos

$ bash    # Open a new shell
$ echo $test
# (empty — not inherited!)
$ exit

Exported variable (inherited by children):

$ export test="kronos"
$ echo $test
kronos

$ bash    # Open a new shell
$ echo $test
kronos    # ✅ Inherited!
$ exit

Key difference:

Type	Command	Inherited by child processes?
Shell variable	`VAR=value`	❌ No
Environment variable	`export VAR=value`	✅ Yes

Verifying Export

$ export test="kronos"
$ echo $test
kronos

$ printenv test
kronos

$ env | grep test
test=kronos

The `set` Command

Without arguments, set prints all variables — including shell variables and functions:

$ set
BASH=/bin/bash
BASH_VERSION=5.1.16
HOME=/home/kronos
HOSTNAME=olympos
...

With arguments, set is used to configure shell options:

$ set -e           # Exit on error
$ set -x           # Debug mode (print each command)
$ set +x           # Disable debug mode

set vs export:

Command	Purpose
`set`	Show all variables (shell + environment + functions)
`export`	Show only environment variables
`export -p`	Show only exported variables

Examples:

# All variables
$ set | head -20

# Only environment variables
$ export -p

# Environment variables (alternative)
$ env

Exporting Functions

$ myfunc() {
    echo "Hello from myfunc!"
}

$ export -f myfunc
$ bash
$ myfunc
Hello from myfunc!
$ exit

Use case: Pass helper functions to sub-shells or scripts.

Making Variables Permanent

echo "export VAR_NAME='value'" >> ~/.bashrc
source ~/.bashrc

Step-by-step:

1. Add to ~/.bashrc:

$ echo "export VAR_NAME='value'" >> ~/.bashrc

2. Reload the config:

$ source ~/.bashrc

3. Verify:

$ echo $VAR_NAME
value

Example — Setting a Permanent Variable

# Set EDITOR permanently
$ echo "export EDITOR='nano'" >> ~/.bashrc
$ source ~/.bashrc

$ echo $EDITOR
nano

# Now any program using $EDITOR will use nano
$ crontab -e     # Opens in nano

More examples:

# Add a custom directory to PATH
echo 'export PATH="$PATH:$HOME/bin"' >> ~/.bashrc
source ~/.bashrc

# Set default language
echo "export LANG='en_US.UTF-8'" >> ~/.bashrc

# Set Java home
echo "export JAVA_HOME='/usr/lib/jvm/java-17-openjdk'" >> ~/.bashrc
echo 'export PATH="$JAVA_HOME/bin:$PATH"' >> ~/.bashrc
source ~/.bashrc

Complete Example Session

# ============================================
# PART 1: VIEWING VARIABLES WITH PRINTENV
# ============================================

$ printenv USER
kronos

$ printenv HOME
/home/kronos

$ printenv PATH
/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin

$ printenv SHELL
/bin/bash

$ printenv PWD
/home/kronos

$ printenv LANG
en_US.UTF-8

$ printenv HOSTNAME
olympos

$ printenv DISPLAY
:0

# All variables
$ printenv | head -15
SHELL=/bin/bash
PWD=/home/kronos
LOGNAME=kronos
HOME=/home/kronos
LANG=en_US.UTF-8
...

# ============================================
# PART 2: VIEWING WITH ECHO
# ============================================

$ echo $USER
kronos

$ echo $HOME
/home/kronos

$ echo "User: $USER, Shell: $SHELL"
User: kronos, Shell: /bin/bash

$ echo $PATH
/usr/local/bin:/usr/bin:/bin

# ============================================
# PART 3: SETTING TEMPORARY VARIABLES
# ============================================

# Shell variable (not exported)
$ test="kronos"
$ echo $test
kronos

$ bash
$ echo $test
# (empty — not inherited)
$ exit

# Environment variable (exported)
$ export test="kronos"
$ echo $test
kronos

$ printenv test
kronos

$ bash
$ echo $test
kronos    # ✅ Inherited!
$ exit

# ============================================
# PART 4: LISTING EXPORTED VARIABLES
# ============================================

$ export -p
declare -x HOME="/home/kronos"
declare -x LANG="en_US.UTF-8"
declare -x PATH="/usr/local/bin:/usr/bin:/bin"
declare -x SHELL="/bin/bash"
declare -x USER="kronos"
...

$ env | head -10
SHELL=/bin/bash
PWD=/home/kronos
LOGNAME=kronos
HOME=/home/kronos
...

# ============================================
# PART 5: SET COMMAND
# ============================================

# Show all variables
$ set | head -20
BASH=/bin/bash
BASHOPTS=checkwinsize:cmdhist:...
BASH_VERSION=5.1.16(1)
...

# Enable debug mode
$ set -x
+ echo hello
hello
$ set +x
# Disable debug mode

# ============================================
# PART 6: MAKING VARIABLES PERMANENT
# ============================================

# Add to ~/.bashrc
$ echo "export EDITOR='nano'" >> ~/.bashrc
$ echo "export MY_NAME='kronos'" >> ~/.bashrc

# Reload
$ source ~/.bashrc

# Verify
$ echo $EDITOR
nano
$ echo $MY_NAME
kronos

# ============================================
# PART 7: PRACTICAL EXAMPLES
# ============================================

# Custom command path
$ mkdir -p ~/bin
$ echo 'export PATH="$PATH:$HOME/bin"' >> ~/.bashrc
$ source ~/.bashrc
$ echo $PATH
/usr/local/bin:/usr/bin:/bin:/home/kronos/bin

# Set Java environment
$ echo 'export JAVA_HOME="/usr/lib/jvm/java-17-openjdk"' >> ~/.bashrc
$ echo 'export PATH="$JAVA_HOME/bin:$PATH"' >> ~/.bashrc
$ source ~/.bashrc
$ java -version

# Development environment
$ echo "export NODE_ENV='development'" >> ~/.bashrc
$ echo "export DEBUG=true" >> ~/.bashrc
$ source ~/.bashrc

# ============================================
# PART 8: EXPORT FUNCTIONS
# ============================================

$ greet() {
    echo "Hello, $USER!"
}

$ export -f greet
$ bash
$ greet
Hello, kronos!
$ exit

# ============================================
# PART 9: UNEXPORT AND UNSET
# ============================================

# Remove export flag (keeps variable)
$ export -n test
$ echo $test       # Still works
kronos
$ bash
$ echo $test       # Not inherited
# (empty)
$ exit

# Remove variable entirely
$ unset test
$ echo $test
# (empty)

Quick Reference

Viewing Variables

Command	Description
`printenv`	Show all environment variables
`printenv VAR`	Show specific variable
`echo $VAR`	Show variable (quick)
`env`	Show all env variables
`set`	Show all variables + functions
`export -p`	Show only exported variables

Setting Variables

Command	Description
`VAR=value`	Shell variable (not exported)
`export VAR=value`	Environment variable (exported)
`export -f func`	Export a function
`export -n VAR`	Remove export flag
`unset VAR`	Remove variable entirely

Common Variables

Variable	Meaning
`HOME`	Home directory
`USER`	Username
`PATH`	Command search path
`PWD`	Current directory
`SHELL`	Current shell
`LANG`	Language setting
`HOSTNAME`	Machine name
`EDITOR`	Default editor
`DISPLAY`	X display
`TERM`	Terminal type

Best Practices

✅ Do This:

# Check a variable before using it
if [ -z "$EDITOR" ]; then
    export EDITOR=nano
fi

# Use quotes when displaying variables
echo "$HOME"                    # ✅
echo "$USER is logged in"

# Add to PATH correctly
export PATH="$PATH:$HOME/bin"   # ✅ Append, don't replace

# Make permanent in ~/.bashrc
echo 'export EDITOR=nano' >> ~/.bashrc
source ~/.bashrc

# Use printenv to check existence
if printenv MY_VAR > /dev/null 2>&1; then
    echo "MY_VAR is set"
fi

# Export only what's needed
export PROJECT_HOME="/home/kronos/projects"

❌ Don’t Do This:

# Don't forget to export when you need inheritance
test="value"          # ❌ Not inherited by children
export test="value"   # ✅

# Don't replace PATH — always append
export PATH="/home/kronos/bin"          # ❌ Breaks commands!
export PATH="$PATH:/home/kronos/bin"    # ✅

# Don't store secrets in ~/.bashrc
export PASSWORD="secret123"   # ❌ Insecure!

# Don't forget to source after editing
nano ~/.bashrc
# ... add export ...
source ~/.bashrc              # ✅ Required

# Don't use single quotes when you need expansion
echo 'User: $USER'            # ❌ Shows $USER literally
echo "User: $USER"            # ✅ Expands

# Don't overwrite important variables
export HOME="/tmp"            # ❌ Breaks everything!

Common Pitfalls

Pitfall	Problem	Solution
Forgot `export`	Variable not inherited	Add `export`
Replaced PATH	Commands not found	Use `$PATH:` prefix
`'$VAR'` in quotes	Literal `$VAR` shown	Use `"$VAR"`
Edited `.bashrc` without source	Changes not applied	`source ~/.bashrc`
Variable lost after reboot	Not saved	Add to `~/.bashrc`
Spaces around `=`	Error	`VAR=value` (no spaces)

Real-World Examples

1. Add Custom Scripts Directory

# Create the directory
$ mkdir -p ~/bin

# Add to PATH permanently
$ echo 'export PATH="$PATH:$HOME/bin"' >> ~/.bashrc
$ source ~/.bashrc

# Now any script in ~/bin can be run from anywhere
$ cp myscript.sh ~/bin/
$ chmod +x ~/bin/myscript.sh
$ myscript.sh    # ✅ Works from anywhere

2. Set Default Editor

# Set nano as default editor
$ echo 'export EDITOR=nano' >> ~/.bashrc
$ source ~/.bashrc

# Now uses nano
$ crontab -e       # Opens in nano
$ git commit       # Uses nano for commit message
$ visudo           # Uses nano

3. Development Environment Variables

# Add to ~/.bashrc
export NODE_ENV=development
export DATABASE_URL="postgres://localhost:5432/myapp"
export API_KEY="dev-key-12345"
export DEBUG=true

source ~/.bashrc

4. Java Development Setup

# Add to ~/.bashrc
export JAVA_HOME="/usr/lib/jvm/java-17-openjdk"
export PATH="$JAVA_HOME/bin:$PATH"
export MAVEN_HOME="/opt/maven"
export PATH="$MAVEN_HOME/bin:$PATH"

source ~/.bashrc
$ java -version
openjdk version "17.0.2"

5. Display Variable in Shell Prompt

# Add to ~/.bashrc
export PS1='[\u@\h \W]\$ '
# Result: [kronos@olympos ~]$

6. Temporary Override for a Command

# Change locale just for one command
$ LANG=es_ES.UTF-8 date
jue 15 ene 2024 10:35:22 UTC

# Back to normal
$ date
Mon Jan 15 10:35:25 UTC 2024

7. Conditional Variable

# In a script
if [ -z "$DEPLOY_ENV" ]; then
    export DEPLOY_ENV="staging"
fi

echo "Deploying to: $DEPLOY_ENV"

8. Show What’s Changed

# Compare current env with defaults
$ printenv | sort > current-env.txt
$ diff /etc/environment current-env.txt

Visual: Variable Inheritance

┌──────────────────────────────────────────────┐
│           Parent Shell (bash)                │
│                                              │
│  VAR="value"          ← Shell variable       │
│  export EVAR="value"  ← Environment variable │
│                                              │
└─────────────────┬────────────────────────────┘
                  │ forks
                  ▼
┌──────────────────────────────────────────────┐
│           Child Process (bash)               │
│                                              │
│  echo $VAR            → (empty!)             │
│  echo $EVAR           → value ✅             │
│                                              │
│  Only EVAR is inherited!                     │
└──────────────────────────────────────────────┘

Summary

Command	Purpose	Example
`printenv`	View env variables	`printenv USER`
`echo $VAR`	Quick view	`echo $HOME`
`export VAR=value`	Set env variable	`export EDITOR=nano`
`export -p`	List exported	`export -p`
`export -n VAR`	Remove export flag	`export -n test`
`unset VAR`	Delete variable	`unset test`
`set`	Show all variables	`set \| head`
`env`	Show env variables	`env`

Key takeaways:

Environment variables are key-value pairs inherited by child processes
printenv shows all env variables — printenv VAR shows one
echo $VAR is a quick way to view — great in scripts
Shell variables (VAR=x) are not inherited — environment variables (export VAR=x) are
export -p lists only exported variables
export -f func exports a function to sub-shells
export -n VAR removes the export flag (keeps variable)
unset VAR removes the variable entirely
Permanent variables go in ~/.bashrc — then source ~/.bashrc
Never replace PATH — always append with $PATH:newdir
Common variables: HOME, USER, PATH, PWD, SHELL, LANG, EDITOR, DISPLAY

Remember: The key distinction is between shell variables (local to the current shell) and environment variables (inherited by child processes). Use export to make a variable available everywhere. Use printenv to view environment variables and echo $VAR for quick checks. For permanent changes, add to ~/.bashrc and remember to source it. And when modifying PATH, always use $PATH:newdir — never replace the whole thing!

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