Overview
The export command sets or modifies environment variables in the current Nash shell session. Variables set with export are available to all commands executed in the current session and any subshells.
Syntax
export KEY=VALUE [KEY=VALUE...]
Description
The export command sets environment variables using KEY=VALUE syntax. Multiple variables can be set in a single command. The variables are immediately available to all subsequent commands and persist for the duration of the shell session.
In Nash, variables must be set with export to be available. Unlike standard bash, Nash does not support setting variables without export.
Options
The export command does not accept any flags or options. It only accepts KEY=VALUE assignments.
Examples
Set a Single Variable
export API_KEY=abc123
echo $API_KEY
# Output: abc123
Set Multiple Variables
export HOST=localhost PORT=8080 DEBUG=true
echo $HOST:$PORT
# Output: localhost:8080
Set Variable with Spaces
export MESSAGE="Hello, World!"
echo $MESSAGE
# Output: Hello, World!
Update Existing Variable
export PATH=/custom/bin
env | grep PATH
# Output: PATH=/custom/bin
Append to PATH
export PATH=$PATH:/new/path
echo $PATH
# Output: /usr/local/bin:/usr/bin:/bin:/new/path
Set Empty Value
export EMPTY=
env | grep EMPTY
# Output: EMPTY=
Use Command Substitution
export CURRENT_DIR=$(pwd)
echo $CURRENT_DIR
# Output: /home/user
export DB_HOST=localhost DB_PORT=5432 DB_NAME=myapp
echo "Database: $DB_HOST:$DB_PORT/$DB_NAME"
# Output: Database: localhost:5432/myapp
Practical Use Cases
# Set application configuration
export APP_ENV=production
export LOG_LEVEL=info
export MAX_CONNECTIONS=100
# Verify settings
env | grep APP
API Configuration
# Set API credentials
export API_URL=https://api.example.com
export API_KEY=secret_key_here
export API_TIMEOUT=30
Development Environment
# Set development variables
export NODE_ENV=development
export DEBUG=true
export PORT=3000
# Configure editor
export EDITOR=nano
# Set default pager
export PAGER=less
Build Configuration
# Set build flags
export BUILD_TYPE=release
export TARGET_ARCH=x86_64
export OPTIMIZATION=-O2
Session Customization
# Customize prompt (if supported)
export PS1="[\u@\h \W]\$ "
# Set history size
export HISTSIZE=1000
Variable Naming Conventions
Environment variables are conventionally named in UPPERCASEexport API_KEY=value
export DATABASE_URL=postgres://...
Use underscores to separate words, not hyphens or spacesexport MY_VARIABLE=value # Good
export MY-VARIABLE=value # Bad (won't work)
No spaces around the equals signexport KEY=VALUE # Good
export KEY = VALUE # Bad (won't work)
Variable Expansion
Variables can be referenced in several ways:
export NAME=Alice
# Basic expansion
echo $NAME
# Output: Alice
# Braced expansion (recommended for clarity)
echo ${NAME}
# Output: Alice
# Use in strings
echo "Hello, $NAME!"
# Output: Hello, Alice!
# Use in command substitution
export GREETING="Hello, $(echo $NAME)"
echo $GREETING
# Output: Hello, Alice
Subshell Behavior
Variables are inherited by subshells:
export OUTER=value
# Subshell inherits variable
(echo $OUTER)
# Output: value
# Changes in subshell don't affect parent
(export OUTER=changed; echo $OUTER)
# Output: changed
echo $OUTER
# Output: value (unchanged)
Common Patterns
Load Configuration from File
# config.env contains:
# export API_KEY=abc123
# export API_URL=https://api.example.com
cat config.env
# Then manually export or source if supported
Conditional Export
# Set default if not already set
test -z "$PORT" && export PORT=8080
Export with Fallback
# Use environment variable or default
export LOG_LEVEL=${LOG_LEVEL:-info}
# Note: Parameter expansion may not be fully supported in Nash
Notes
- Variables persist only for the current shell session
- Variables are not saved between Nash sessions
- Use
.nashrc to set variables on every startup
- Variable names are case-sensitive
- Special characters in values should be quoted
- Spaces around
= will cause syntax errors
- Variable names cannot start with numbers
- Avoid overwriting critical system variables like PATH without preserving the original value
Exit Status
The export command always returns exit code 0 (success).
- env - Display all environment variables
- unset - Remove environment variables
- echo - Display variable values
- test - Test variable values and conditions
