env

env

The env command in Unix-like operating systems is used to manage the environment for processes. It can be used to display the current environment variables, set new environment variables, or run commands with a modified environment. Here's an overview of the env command and its usage:

Overview of env

Purpose: The env command is used to run a command in a modified environment or to display the current environment variables.

Basic Syntax

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

Common Uses and Examples

1. Display Environment Variables:

   • Running env without any arguments will list all the current environment variables and their values.

     env

     Example output:

     PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
     HOME=/home/user
     USER=user
     SHELL=/bin/bash

2. Run a Command with Modified Environment Variables:

   • You can use env to set environment variables for a single command execution without altering the global environment.

     env VAR=value command

     For example, to run echo $VAR with VAR set to hello:

     env VAR=hello echo $VAR

     Output:

     hello

3. Remove All Environment Variables:

   • You can use the -i or --ignore-environment option to clear all environment variables and run a command in a clean environment.

     env -i command

     For example, to run a shell with no environment variables:

     env -i /bin/bash --noprofile --norc

4. Unset an Environment Variable:

   • You can use env to run a command with specific environment variables unset.

     env -u VAR command

     For example, to run printenv without the USER environment variable:

     env -u USER printenv

Practical Examples

1. Temporary PATH Modification:

   • Run a command with a modified PATH variable without changing the global PATH.

     env PATH=/custom/path:$PATH some_command

2. Debugging with a Clean Environment:

   • Run a script or command in a clean environment to debug issues caused by environment variables.

     env -i /path/to/script.sh

3. Setting Multiple Variables:

   • You can set multiple environment variables for a command execution.

     env VAR1=value1 VAR2=value2 command

     For example:

     env DB_HOST=localhost DB_USER=root /path/to/db_connect_script.sh

Environment Variables

Environment variables are key-value pairs that influence the behavior of processes and applications in the shell. Common environment variables include:

• PATH: Specifies the directories to search for executable files.

• HOME: Indicates the home directory of the current user.

• USER: Represents the name of the current user.

• SHELL: Specifies the path to the current shell.

Conclusion

The env command is a versatile tool for managing environment variables and running commands in customized environments. It's particularly useful for testing, debugging, and scripting, allowing precise control over the execution environment.

help

env [options] [variable=value]

Print or set environment variables.

Options:

-i, --ignore-environment   Do not inherit environment variables from the parent shell.
-u, --unset   Unset environment variable.
-l, --list   List all environment variables.
-v, --verbose   Print each variable and its value.
-P, --path   Print the current $PATH.
-S, --secure   Print environment variables in a secure way.

Examples:

    env
    env HOME=/home/user
    env -i
    env -u HOME
    env -l
    env -v
    env -P
    env -S