env is a

shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard o ...

command Command may refer to: Computing * Command (computing), a statement in a computer language * COMMAND.COM, the default operating system shell and command-line interpreter for DOS * Command key, a modifier key on Apple Macintosh computer keyboards * ...

for

Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, an ...

and

Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also i ...

s. It is used to either print a list of

environment variable An environment variable is a dynamic-named value that can affect the way running processes will behave on a computer. They are part of the environment in which a process runs. For example, a running process can query the value of the TEMP envi ...

s or run another utility in an altered environment without having to modify the currently existing environment. Using env, variables may be added or removed, and existing variables may be changed by assigning new values to them. In practice, env has another common use. It is often used by shell scripts to launch the correct interpreter. In this usage, the environment is typically not changed.

History

The version of env bundled in

GNU GNU () is an extensive collection of free software (383 packages as of January 2022), which can be used as an operating system or can be used in parts with other operating systems. The use of the completed GNU tools led to the family of operat ...

coreutils The GNU Core Utilities or coreutils is a package of GNU software containing implementations for many of the basic tools, such as cat, ls, and rm, which are used on Unix-like operating systems. In September 2002, the ''GNU coreutils'' were cr ...

was written by Richard Mlynarik, David MacKenzie, and Assaf Gordon. It first appeared in 4.4BSD, and is a part of POSIX.1 (with the option only). GNU's has been extended to handle signals and the current directory. FreeBSD's supports a custom search path. Extensions found in both versions include , for unsetting variables, and , for splitting arguments (mainly in shebang).

Examples

To print out the set of current environment variables: env To create a new environment without any existing environment variables for a new shell: env -i /bin/sh To execute the X application

xcalc The X.Org Foundation is a non-profit corporation chartered to research, develop, support, organize, administrate, standardize, promote, and defend a free and open accelerated graphics stack. This includes, but is not limited to, the following p ...

and have it appear on a different display (i.e., with a modified environment whether the specified environment variable is replaced with the new value): env DISPLAY=foo.bar:1.0 xcalc Note that this use of env is often unnecessary since most shells support setting environment variables in front of a command: DISPLAY=foo.bar:1.0 xcalc env may also be used in the

hashbang In computing, a shebang is the character sequence consisting of the characters number sign and exclamation mark () at the beginning of a script. It is also called sharp-exclamation, sha-bang, hashbang, pound-bang, or hash-pling. When a text fil ...

line of a script to allow the interpreter to be looked up via the PATH. For example, here is the code of a

Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (pro ...

script: #!/usr/bin/env python3 print("Hello, World!") In this example, /usr/bin/env is the full

path A path is a route for physical travel – see Trail. Path or PATH may also refer to: Physical paths of different types * Bicycle path * Bridle path, used by people on horseback * Course (navigation), the intended path of a vehicle * Desire p ...

of the env command. The environment is not altered. Note that it is possible to specify the interpreter without using env, by giving the full path of the python interpreter. A problem with that approach is that on different computer systems, the exact path may be different. By instead using env as in the example, the interpreter is searched for and located at the time the script is run (more precisely, env does a system call to execvp, which does the job of locating the interpreter and launching it). This makes the script more

portable Portable may refer to: General * Portable building, a manufactured structure that is built off site and moved in upon completion of site and utility work * Portable classroom, a temporary building installed on the grounds of a school to provide ...

, but also increases the risk that the wrong interpreter is selected because it searches for a match in every directory on the executable search path. It also suffers from the same problem in that the path to the env binary may also be different on a per-machine basis.

References

External links

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. * * * * * {{Core Utilities commands Standard Unix programs Unix SUS2008 utilities Inferno (operating system) commands IBM i Qshell commands Environment variables

History

Examples

See also

References

External links