Environment variables

Environment variables
You are encouraged to solve this task according to the task description, using any language you may know.

Show how to get one of your process's environment variables. The available variables vary by system; some of the common ones available on Unix include PATH, HOME, USER.

Ada

Print a single environment variable. <lang ada>with Ada.Environment_Variables; use Ada.Environment_Variables; with Ada.Text_Io; use Ada.Text_Io;

procedure Print_Path is begin

  Put_Line("Path : " & Value("PATH"));

end Print_Path;</lang> Print all environment variable names and values. <lang ada>with Ada.Environment_Variables; use Ada.Environment_Variables; with Ada.Text_Io; use Ada.Text_Io;

procedure Env_Vars is

  procedure Print_Vars(Name, Value : in String) is
  begin
     Put_Line(Name & " : " & Value);
  end Print_Vars;

begin

  Iterate(Print_Vars'access);

end Env_Vars;</lang>

ALGOL 68

Works with: ALGOL 68G version Any - tested with release mk15-0.8b.fc9.i386 - getenv is not part of the standard's prelude

<lang algol68>print((getenv("HOME"), new line))</lang>

AutoHotkey

<lang autohotkey>EnvGet, OutputVar, Path MsgBox, %OutputVar%</lang>

AWK

The ENVIRON array contains the values of the current environment: <lang awk>$ awk 'BEGIN{print "HOME:"ENVIRON["HOME"],"USER:"ENVIRON["USER"]}' HOME:/home/suchrich USER:SuchRich</lang> Environment variables can also be assigned to awk variables before execution, with (-v) options: <lang awk>$ awk -v h=$HOME -v u=$USER 'BEGIN{print "HOME:"h,"USER:"u}' HOME:/home/suchrich USER:SuchRich</lang>

BASIC

<lang qbasic>x$ = ENVIRON$("path") PRINT x$ </lang>

ZX Spectrum Basic

The ZX Spectrum does not use environmental variables in a traditional sense. However, it does provide a set of system variables held at a fixed memory address:

<lang zxbasic> 10 PRINT "The border colour is "; PEEK (23624): REM bordcr 20 PRINT "The ramtop address is "; PEEK (23730) + 256 * PEEK (23731): REM ramtop 30 POKE 23609,50: REM set keyboard pip to 50 </lang>

Batch File

Batch files don't have any other kind of variables except environment variables. They can be accessed by enclosing the variable name in percent signs: <lang dos>echo %Foo%</lang> For interactive use one can use set to view all environment variables or all variables starting with a certain string: <lang dos>set set Foo</lang>

BBC BASIC

Works with: BBC BASIC for Windows

<lang bbcbasic> PRINT FNenvironment("PATH")

     PRINT FNenvironment("USERNAME")
     END
     
     DEF FNenvironment(envar$)
     LOCAL buffer%, size%
     SYS "GetEnvironmentVariable", envar$, 0, 0 TO size%
     DIM buffer% LOCAL size%
     SYS "GetEnvironmentVariable", envar$, buffer%, size%+1
     = $$buffer%</lang>

C

<lang c>#include <stdlib.h>

1. include <stdio.h>

int main() {

 puts(getenv("HOME"));
 return 0;

}</lang>

C++

<lang cpp>#include <cstdlib>

1. include <cstdio>

int main() {

  puts(getenv("HOME"));
  return 0;

}</lang>

C#

<lang csharp>using System;

namespace RosettaCode {

   class Program {
       static void Main() {
           string temp = Environment.GetEnvironmentVariable("TEMP");
           Console.WriteLine("TEMP is " + temp);
       }
   }

}</lang>

Clojure

<lang lisp> (System/getenv "HOME") </lang>

D

Library: phobos

<lang d>import std.stdio, std.process;

void main() {

   writeln(getenv("HOME"));

}</lang>

Library: tango

<lang d>import tango.sys.Environment;

void main() {

   auto home = Environment("HOME");

}</lang>

Common Lisp

Access to environment variables isn't a part of the Common Lisp standard, but most implementations provide some way to do it.

Works with: LispWorks

<lang lisp>(lispworks:environment-variable "USER")</lang>

Works with: SBCL

<lang lisp>(sb-ext:posix-getenv "USER")</lang>

Works with: Clozure CL

<lang lisp>(ccl:getenv "USER")</lang>

Ways to do this in some other implementations are listed in the Common Lisp Cookbook.

Delphi

<lang Delphi>program EnvironmentVariable;

{$APPTYPE CONSOLE}

uses SysUtils;

begin

 WriteLn('Temp = ' + GetEnvironmentVariable('TEMP'));

end.</lang>

E

Works with: E-on-Java

<lang e><unsafe:java.lang.System>.getenv("HOME")</lang>

Eiffel

The feature get returns the value of an environment variable. get is defined in the library class EXECUTION_ENVIRONMENT. So the class APPLICATION inherits from EXECUTION_ENVIRONMENT in order to make get available.

<lang eiffel >class

   APPLICATION

inherit

   EXECUTION_ENVIRONMENT

create

   make

feature {NONE} -- Initialization

   make
           -- Retrieve and print value for environment variable `USERNAME'.
       do
           print (get ("USERNAME"))
       end

end</lang>

Emacs Lisp

<lang lisp>(getenv "HOME")</lang>

Euphoria

<lang euphoria>puts(1,getenv("PATH"))</lang>

Factor

<lang factor>"HOME" os-env print</lang>

Forth

Works with: GNU Forth

<lang forth>s" HOME" getenv type</lang>

Fortran

Works with: any Fortran compiler

<lang fortran> program show_home implicit none character(len=32) :: home_val  ! The string value of the variable HOME integer  :: home_len  ! The actual length of the value integer  :: stat  ! The status of the value:

                              !  0 = ok
                              !  1 = variable does not exist
                              ! -1 = variable is not long enought to hold the result

call get_environment_variable('HOME', home_val, home_len, stat) if (stat == 0) then

   write(*,'(a)') 'HOME = '//trim(home_val)

else

   write(*,'(a)') 'No HOME to go to!'

end if end program show_home </lang>

Go

Simply: <lang go> package main

import (

   "fmt"
   "os"

)

func main() {

   fmt.Println(os.Getenv("SHELL"))

}</lang> Output:

/bin/bash

Alternatively:

Library function os.Environ returns all environment variables. You're on your own then to parse out the one you want. Example: <lang go>package main

import (

   "fmt"
   "os"
   "strings"

)

func main() {

   s := "SHELL"
   se := s + "="
   for _, v := range os.Environ() {
       if strings.HasPrefix(v, se) {
           fmt.Println(s, "has value", v[len(se):])
           return
       }
   }
   fmt.Println(s, "not found")

}</lang> Output:

SHELL has value /bin/bash

Haskell

<lang haskell>import System.Environment main = do getEnv "HOME" >>= print -- get env var

         getEnvironment >>= print -- get the entire environment as a list of (key, value) pairs</lang>

HicEst

<lang HicEst>CHARACTER string*255

string = "PATH=" SYSTEM(GEteNV = string)</lang>

Icon and Unicon

Works with: Unicon

<lang Icon>procedure main(arglist)

if *envars = 0 then envars := ["HOME", "TRACE", "BLKSIZE","STRSIZE","COEXPSIZE","MSTKSIZE", "IPATH","LPATH","NOERRBUF"]

every v := !sort(envars) do

  write(v," = ",image(getenv(v))|"* not set *")

end</lang>

J

<lang j>2!:5'HOME'</lang>

Java

<lang java>System.getenv("HOME") // get env var System.getenv() // get the entire environment as a Map of keys to values</lang>

JavaScript

The JavaScript language has no facilities to access the computer: it relies on the host environment to provide it.

Works with: JScript

<lang javascript>var shell = new ActiveXObject("WScript.Shell"); var env = shell.Environment("PROCESS"); WScript.echo('SYSTEMROOT=' + env.item('SYSTEMROOT'));</lang>

Joy

<lang joy>"HOME" getenv.</lang>

Liberty BASIC

Built-in variables

<lang lb>print StartupDir$ print DefaultDir$</lang>

Other variables

<lang lb>print GetEnvironmentVariable$("USERNAME")

   print GetEnvironmentVariable$("USERPROFILE") ' equivalent to UNIX HOME variable
   print GetEnvironmentVariable$("PATH")
   end

function GetEnvironmentVariable$(lpName$)

   'get the value of an environment variable
   nSize = 1024

[Retry]

   lpBuffer$ = space$(nSize)

   calldll #kernel32, "GetEnvironmentVariableA", _
       lpName$   as ptr, _
       lpBuffer$ as ptr, _
       nSize     as ulong, _
       result    as ulong

   select case
       ' buffer too small
       case result > nSize
       nSize = result
       goto [Retry]

       ' variable found
       case result > 0
       GetEnvironmentVariable$ = left$(lpBuffer$, result)
   end select

end function</lang>

Lua

<lang lua>print( os.getenv( "PATH" ) )</lang>

Mathematica

<lang Mathematica>Environment["PATH"]</lang>

MUMPS

ANSI MUMPS doesn't allow access to the operating system except possibly through the View command and $View function, both of which are implementation specific. Intersystems' Caché does allow you to create processes with the $ZF function, and if the permissions for the Caché process allow it you can perform operating system commands.

In Caché on OpenVMS in an FILES-11 filesystem ODS-5 mode these could work:

<lang MUMPS> Set X=$ZF(-1,"show logical")

Set X=$ZF(-1,"show symbol")</lang>

NewLISP

<lang NewLISP>> (env "SHELL") "/bin/zsh" > (env "TERM") "xterm" </lang>

NSIS

While common environment variables exist as constants within the NSIS script compilation environment (see NSIS documentation), arbitrarily-named environment variables' values may be retrieved using ExpandEnvStrings. <lang nsis>ExpandEnvStrings $0 "%PATH%" ; Retrieve PATH and place it in builtin register 0. ExpandEnvStrings $1 "%USERPROFILE%" ; Retrieve the user's profile location and place it in builtin register 1. ExpandEnvStrings $2 "%USERNAME%" ; Retrieve the user's account name and place it in builtin register 2.</lang>

Objective-C

[[NSProcessInfo processInfo] environment] returns an NSDictionary of the current environment. <lang objc>[[[NSProcessInfo processInfo] environment] objectForKey:@"HOME"]</lang>

OCaml

<lang ocaml>Sys.getenv "HOME"</lang>

Oz

<lang oz>{System.showInfo "This is where Mozart is installed: "#{OS.getEnv 'OZHOME'}}</lang>

PARI/GP

<lang parigp>system("echo $HOME")</lang>

Pascal

See Delphi

Perl

The %ENV hash maps environment variables to their values: <lang perl>print $ENV{HOME}, "\n";</lang>

Perl 6

Works with: Rakudo version #24 "Seoul"

The %*ENV hash maps environment variables to their values: <lang perl6>say %*ENV<HOME>;</lang>

PHP

The $_ENV associative array maps environmental variable names to their values: <lang php>$_ENV['HOME']</lang>

PicoLisp

<lang PicoLisp>: (sys "TERM") -> "xterm"

(sys "SHELL")

-> "/bin/bash"</lang>

PowerShell

Environment variables can be found in the Env: drive and are accessed using a special variable syntax: <lang powershell>$Env:Path</lang> To get a complete listing of all environment variables one can simply query the appropriate drive for its contents: <lang powershell>Get-ChildItem Env:</lang>

PureBasic

PureBasic has the built in funtion <lang PureBasic>GetEnvironmentVariable("Name")</lang>

Example <lang PureBasic>If OpenConsole()

 PrintN("Path:"+#CRLF$ + GetEnvironmentVariable("PATH"))
 PrintN(#CRLF$+#CRLF$+"NUMBER_OF_PROCESSORS= "+ GetEnvironmentVariable("NUMBER_OF_PROCESSORS"))

 PrintN(#CRLF$+#CRLF$+"Press Enter to quit.")
 Input() 
 CloseConsole()

EndIf</lang>

Python

The os.environ dictionary maps environmental variable names to their values: <lang python>import os os.environ['HOME']</lang>

R

<lang R>Sys.getenv("PATH")</lang>

REBOL

<lang REBOL>print get-env "HOME"</lang>

Retro

<lang Retro>here "HOME" getEnv here puts</lang>

REXX

Each REXX interpreter sets its own rules by what identify the environmental variables are named.
In addition, each operation system (OS) hase their own definition as well.
This makes it problamatic in the acessing/acquiring of environmental variables.
Most programmers know what REXX interpreter they are using, and furthermore, they also
know what operating system they are writing the REXX program for, so most programmers hard-wire
(explicitly code) the "access-name" of the system environmental variables into the program.

The following will work for Regina and R4 for the DOS shell under Windows (any version). <lang rexx> /*REXX program shows how to get an environmental variable under Windows*/

x=value('TEMP',,'SYSTEM') </lang> The following will work for PC/REXX and Regina for the DOS shell under Windows (any version). <lang rexx> /*REXX program shows how to get an environmental variable under Windows*/

x=value('TEMP',,'ENVIRONMENT') </lang> Other REXX interpreters have their own requirements to identify the SYSTEM environment.
VM/CMS has something called GLOBALV (global variables) and are of three types:
* temporary (lasting only for execution of the REXX program),
* temporary (lasting only for LOGON or CMS session),
* permanent.

As such, CMS has its own command interface for these variables.

Ruby

The ENV hash maps environmental variable names to their values: <lang ruby>ENV['HOME']</lang>

Seed7

<lang seed7>$ include "seed7_05.s7i";

const proc: main is func

 begin
   writeln(getenv("HOME"));
 end func;</lang>

Slate

<lang slate>Environment variables at: 'PATH'. "==> '/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games'"</lang>

Standard ML

<lang sml>OS.Process.getEnv "HOME"</lang> returns an option type which is either SOME value or NONE if variable doesn't exist

SNOBOL4

Works with: Macro Spitbol

Works with: CSnobol

The host(4) function returns a known environment variable. <lang SNOBOL4> output = host(4,'PATH') end</lang>

Tcl

The env global array maps environmental variable names to their values: <lang tcl>$env(HOME)</lang>

UNIX Shell

In the Unix Shell Language, environment variables are available as ordinary variables: <lang bash>echo $HOME</lang> An ordinary variable can be marked as an environment variable with the export command: <lang bash>export VAR</lang> Now child processes launched by the shell will have an environment variable called VAR.

The Unix command "env" will print out all of the environment variables as key=value pairs on standard output.

Ursala

The argument to the main program is a record initialized by the run-time system in which one of the fields (environs) contains the environment as a list of key:value pairs. <lang Ursala>#import std

1. executable ('parameterized',)

showenv = <.file$[contents: --<>]>+ %smP+ ~&n-={'TERM','SHELL','X11BROWSER'}*~+ ~environs</lang> The rest of this application searches for the three variables named and displays them on standard output. Here is a bash session.

$ showenv
<
   'TERM': 'Eterm',
   'SHELL': '/bin/bash',
   'X11BROWSER': '/usr/bin/firefox'>

Vedit macro language

<lang vedit>Get_Environment(10,"PATH") Message(@10)</lang>

Or with short keywords: <lang vedit>GE(10,"PATH") M(@10)</lang>