Code-Memo

Shell variables and environment

Overview

Shell scripts use:

Shell variables: local to the current shell process
Environment variables: exported to child processes

Assignments and expansion

name="Alice"
echo "$name"

Parameter expansion essentials

${var:-default}: use default if unset/empty
${var:?message}: error if unset/empty
${#var}: length
${var%pattern} / ${var%%pattern}: trim suffix
${var#pattern} / ${var##pattern}: trim prefix

Exporting

API_TOKEN="secret"     # shell variable
export API_TOKEN       # becomes environment variable for children

Common env vars

PATH: command lookup path
HOME: user home directory
PWD: current directory
SHELL: login shell
LANG / LC_*: locale settings
TERM: terminal type

Sourcing vs executing

./script.sh: runs in a new process; variable changes do not persist
source script.sh or . script.sh: runs in current shell; changes persist

Arrays (Bash)

items=("a" "b c" "d")
printf '%s\n' "${items[@]}"

Tips

Prefer readonly for constants: readonly APP_NAME="code-memo"
Use declare -r / declare -a / declare -A when clarity helps