Linux env

env command

Syntax:

env [OPTION]... [-][NAME=VALUE]... [COMMAND [ARG]...]

Options of env command

  1. Without any argument: print out a list of all environment variables
    • Syntax: env
  2. -i or –ignore-environment or only –: runs a command with an empty environment
    • Syntax: env -i your_command
    • Example: env -i /bin/sh
  3. -u or –unset: remove variable from the environment
    • Syntax: env -u variable_name
  4. -0 or –null: End each output line with NULL, not newline
    • Syntax: env -0
  5. –version: Display version information and exit
    • Syntax: env --version
  6. –help: Display a help message and exit
    • Syntax: env --help

Environment Variables

To set a global ENV

$ export NAME=Value
or
$ set NAME=Value

To set a local ENV

$ NAME=Value

To set user wide ENVs

~/.bashrc, ~/.bash_profile, ~/.bash_login, ~/.profile

$ sudo vi ~/.bashrc
export NAME=Value
$ source ~/.bashrc

To set system wide ENVs

/etc/environment, /etc/profile, /etc/profile.d/, /etc/bash

$ sudo -H vi /etc/environment
NAME=Value

Unset environment variables

$ unset NAME
or
$ NAME=''

Some commonly used ENVs in Linux

$USER: Gives current user's name.
$PATH: Gives search path for commands.
$PWD: Gives the path of present working directory.
$HOME: Gives path of home directory.
$HOSTNAME: Gives name of the host.
$LANG: Gives the default system language.
$EDITOR: Gives default file editor.
$UID: Gives user ID of current user.
$SHELL: Gives location of current user's shell program.

Example

echo $HOSTNAME
echo $SHELL
echo $HISTSIZE
echo $USER
echo $PATH
echo $PWD
echo $LANG
echo $HOME
echo $RANDOM