Environment Variables

The state every program reads

Environment variables are key/value pairs every running process can read. $HOME, $PATH, $USER, $LANG — all of them shape how programs behave. printenv prints them all; echo $VAR shows one.

Set, export, unset

VAR=value — local to this shell only.
export VAR=value — passed to every child process.
unset VAR — remove it.
VAR=value cmd — set just for one invocation. HTTPS_PROXY=... curl ... is the canonical example.

Why export matters

Without export, the value lives only in the current shell. If you spawn python script.py and the script reads os.environ['VAR'], it sees nothing. Always export for tools to pick it up.

The variables you'll touch

$PATH — executable lookup.
$HOME — your home dir.
$EDITOR — what git commit opens (set to nvim, code -w, cursor -w).
$PAGER — what man uses (set to less -R).
$LANG / $LC_* — locale and character set.
$TERM — terminal type.

Where to set them

Interactive use → ~/.zshrc. Login-time only → ~/.zprofile. The full breakdown is the next lesson; for now remember that one of those files is the right place.

Code

Inspect and set·bash

printenv | head
echo $EDITOR $PAGER $SHELL
# Set for this shell only
FOO=bar
echo $FOO
# Set for children
export FOO=bar
python3 -c 'import os; print(os.environ.get("FOO"))'

Per-command environment·bash

HTTPS_PROXY=http://proxy:8080 curl https://example.com
DEBUG=1 ./run.sh
# Doesn't pollute the shell — verify
echo $DEBUG

The state every program reads

Set, export, unset

Why export matters

The variables you'll touch

Where to set them

Code

External links

Exercise

Progress

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