Bash variables are one of the first things you’ll encounter when using Linux — but there’s a big difference between shell variables, environment variables, and how to make them persist globally.
This guide will take you from the basics, with clear examples.
1. What Is a Variable?
A variable is just a named value stored in memory that the shell (or a program) can use.
MY_NAME="Derek"
echo "Hello, $MY_NAME"
Output:
Hello, Derek
No spaces allowed around the equal sign. Quotes are optional unless your value contains spaces.
2. Shell Variables vs. Environment Variables
Here’s where most confusion starts.
Shell Variable
- Exists only inside your current shell session.
- Other programs cannot see it.
MY_VAR="test"
echo $MY_VAR # works
env | grep MY_VAR # it doesn't exist in the environment variables
Environment Variable
- Exists in the environment of the shell.
- Is exported so that all programs you run can see it.
export MY_VAR="test"
env | grep MY_VAR # shows MY_VAR=test
Now, any command you run (even in that session) can access it.
3. Temporary Variables (Session-Only)
You can set a variable temporarily in two ways:
Option 1: Normal + export
MY_VAR="hello"
export MY_VAR
Or in one line:
export MY_VAR="hello"
This lasts until you close the shell.
Option 2: Inline for One Command
You can set a variable just for a single command:
MY_VAR="hello" some_program
some_program sees MY_VAR, but the variable does not stay in your environment after that command finishes.
4. Reading Variables
You can check what’s currently set:
echo "$MY_VAR" # prints variable contents
set # shows all shell variables
env # shows only exported (environment) variables
5. Unsetting Variables
Remove a variable completely:
unset MY_VAR
6. Making Variables Global (Permanent)
You often want variables to persist across sessions.
To do this, you add them to a shell startup file.
Per-User (Recommended)
Edit ~/.bashrc (or ~/.bash_profile on some systems):
nano ~/.bashrc
Add at the end:
export MY_VAR="hello world"
Then reload:
source ~/.bashrc
Now it will load every time you open a new terminal.
System-Wide (For All Users)
Place them in /etc/environment or /etc/profile.d/custom.sh.
Example /etc/profile.d/myvars.sh:
export COMPANY_NAME="Proport"
export DB_HOST="db.internal"
Save and run:
sudo chmod +x /etc/profile.d/myvars.sh
These will apply to all users on login.
7. Special Built-In Variables
Some variables are set automatically by Bash:
| Variable | Description |
|---|---|
$HOME | Your home directory |
$USER | Your username |
$PATH | Directories searched for commands |
$PWD | Current working directory |
$? | Exit status of last command (0 = success) |
$$ | PID of current shell |
You can modify some of these (e.g. extend $PATH):
export PATH="$PATH:/opt/my-tools/bin"
8. Best Practices ⭐⭐⭐⭐⭐
✅ Quote your variables – prevents problems with spaces:
echo "$MY_VAR"
✅ Use UPPERCASE for environment variables – by convention.
✅ Don’t over-export – only export what other processes need.
✅ Use inline variables for one-off commands – keeps environment clean.
✅ Store permanent variables in .bashrc – so they survive reboots.
9. Quick Visual Summary
# Local shell variable (not visible to programs)
FOO="bar"
# Make it visible to child processes
export FOO
# Or do it in one line
export FOO="bar"
# Or just for one command
FOO="bar" some_program
10. Debugging Tip
Run a program with env in front to see what variables it sees:
env | grep VAULT
Great for checking if something like VAULT_ADDR or VAULT_NAMESPACE is actually being passed before you run vault.
Final Thoughts
If you keep these rules in mind, you’ll never be confused about why a variable “disappears” between commands or why a program can’t see it.
Think of it like working at McDonald’s:
- A shell variable is like telling just your team member at the till.
- An environment variable is like putting it on the kitchen screen for the whole restaurant to see.
- A permanent variable is like updating the store recipe — every shift after that follows it automatically.
Master these, and you’ve definitely earned your ⭐⭐⭐⭐⭐ badge. 😉