# env — Manage Environment Variables in the Shell > View, set, export and unset environment variables in the shell – plus PATH management, .env files and the portable env shebang. Source: https://www.jpkc.com/db/en/cheatsheets/shell-system/env/ Environment variables control how programs behave: from the search `PATH` and the locale `LANG` to API keys and proxy settings. `env` is the tool you reach for to inspect those variables, set one cleanly for a single invocation, or reset the environment entirely – and together with the shell builtins `export` and `unset` you manage the whole lifecycle. This guide walks you through the commands you actually use day to day, from a quick lookup to a clean, reproducible environment. ## View Variables `env` — List all environment variables. ```bash env ``` `env | sort` — List all environment variables sorted alphabetically. ```bash env | sort ``` `printenv` — Print all environment variables (same as env). ```bash printenv ``` `printenv ` — Print the value of a specific variable. ```bash printenv HOME ``` `echo $` — Print a variable's value using shell expansion. ```bash echo $PATH ``` `env | grep ` — Search for variables matching a pattern. ```bash env | grep -i proxy ``` ## Set & Export `export =` — Set and export a variable (available to child processes). ```bash export EDITOR=vim ``` `=` — Set a shell variable (NOT exported to child processes). ```bash MY_VAR=hello ``` `export ` — Export an already-set shell variable. ```bash MY_VAR=hello && export MY_VAR ``` `export -p` — List all exported variables with their values. ```bash export -p ``` `declare -x =` — Declare and export a variable (Bash). ```bash declare -x API_KEY=abc123 ``` ## Unset & Remove `unset ` — Remove a variable completely. ```bash unset TEMP_VAR ``` `export -n ` — Unexport a variable (keep as shell variable only). ```bash export -n MY_VAR ``` `env -u ` — Run a command with a variable removed from environment. ```bash env -u http_proxy curl https://example.com ``` ## Inline & Temporary `= ` — Set a variable for a single command only. ```bash NODE_ENV=production node app.js ``` `env = ` — Run a command with a temporary variable (explicit). ```bash env LANG=C sort data.txt ``` `env -i ` — Run a command with a completely empty environment. ```bash env -i /bin/bash --norc ``` `env -i HOME=$HOME PATH=$PATH ` — Run with clean environment but keep essentials. ```bash env -i HOME=$HOME PATH=$PATH bash -c 'env' ``` ## PATH Management `echo $PATH` — Show the current PATH (colon-separated directories). ```bash echo $PATH ``` `export PATH=":$PATH"` — Prepend a directory to PATH (searched first). ```bash export PATH="$HOME/.local/bin:$PATH" ``` `export PATH="$PATH:"` — Append a directory to PATH (searched last). ```bash export PATH="$PATH:/opt/myapp/bin" ``` `echo $PATH | tr ':' '\n'` — Show PATH entries one per line. ```bash echo $PATH | tr ':' '\n' ``` `which ` — Show which PATH entry a command resolves to. ```bash which python3 ``` ## Common Patterns `source .env` — Load variables from a .env file into the current shell. ```bash source .env ``` `export $(grep -v '^#' .env | xargs)` — Export all non-comment lines from a .env file. ```bash export $(grep -v '^#' .env | xargs) ``` `${VAR:-default}` — Use a default value if variable is unset or empty. ```bash echo ${PORT:-8080} ``` `${VAR:?error message}` — Error and exit if variable is unset or empty. ```bash echo ${DATABASE_URL:?DATABASE_URL must be set} ``` `env -0 | sort -z | tr '\0' '\n'` — Safely list variables (handles values with newlines). ```bash env -0 | sort -z | tr '\0' '\n' ``` ## Conclusion `env` is more than just "list all variables": with `env VAR=value command` you set a variable cleanly for exactly one invocation without touching your shell environment, and with `env -i` you launch a program in a completely empty environment – ideal for reproducible builds and for debugging variable-related issues. `env` is also ubiquitous in the shebang `#!/usr/bin/env python3`: instead of hard-coding a fixed interpreter path, the program is looked up via `PATH`, which keeps scripts portable across systems and virtual environments. A security note: secrets such as API keys or passwords are not truly private as environment variables – depending on the system they show up in `/proc//environ` and are inherited by child processes. For real secrets, dedicated secret managers or files with restrictive permissions are the better choice. And be careful with the popular `export $(grep -v '^#' .env | xargs)`: it breaks on values containing spaces or quotes – for complex `.env` files, prefer `set -a; source .env; set +a`. ## Further Reading - [Wikipedia: Environment variable](https://en.wikipedia.org/wiki/Environment_variable) – fundamentals of environment variables and how they are inherited by child processes - [GNU Coreutils: env invocation](https://www.gnu.org/software/coreutils/manual/html_node/env-invocation.html) – the official reference for env, including `-i`, `-u` and `-0` ## Related Commands - [bash](https://www.jpkc.com/db/en/cheatsheets/shell-system/bash/) – the shell where variables are set, exported and expanded - [id](https://www.jpkc.com/db/en/cheatsheets/shell-system/id/) – shows the user and group IDs that help shape the environment's behaviour - [sudo](https://www.jpkc.com/db/en/cheatsheets/shell-system/sudo/) – run commands with different privileges, including `-E` to preserve the environment