Environment variables: Difference between revisions
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<lang slate>Environment variables at: 'PATH'. |
<lang slate>Environment variables at: 'PATH'. |
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"==> '/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games'"</lang> |
"==> '/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games'"</lang> |
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=={{header|Smalltalk}}== |
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Use the [http://pharo.gemtalksystems.com/book/PharoTools/OSProcess OSProcess] library to gain access to environment variables: |
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<lang smalltalk> |
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OSProcess thisOSProcess environment at: #HOME. |
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OSProcess thisOSProcess environment at: #PATH. |
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OSProcess thisOSProcess environment at: #USER. |
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</lang> |
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=={{header|Standard ML}}== |
=={{header|Standard ML}}== |
Revision as of 13:07, 28 May 2014
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>
Alternative version using Matreshka
Uses Matreshka.
<lang Ada>with Ada.Wide_Wide_Text_IO;
with League.Application; with League.Strings;
procedure Main is
function "+" (Item : Wide_Wide_String) return League.Strings.Universal_String renames League.Strings.To_Universal_String;
begin
Ada.Wide_Wide_Text_IO.Put_Line (League.Application.Environment.Value (+"HOME").To_Wide_Wide_String);
end Main;</lang>
ALGOL 68
<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
<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>
- include <stdio.h>
int main() {
puts(getenv("HOME")); return 0;
}</lang>
C++
<lang cpp>#include <cstdlib>
- 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>
COBOL
<lang cobol> IDENTIFICATION DIVISION.
PROGRAM-ID. Environment-Vars.
DATA DIVISION. WORKING-STORAGE SECTION. 01 home PIC X(75).
PROCEDURE DIVISION.
- *> Method 1.
ACCEPT home FROM ENVIRONMENT "HOME" DISPLAY home
- *> Method 2.
DISPLAY "HOME" UPON ENVIRONMENT-NAME ACCEPT home FROM ENVIRONMENT-VALUE
GOBACK .</lang>
CoffeeScript
<lang coffeescript>for var_name in ['PATH', 'HOME', 'LANG', 'USER']
console.log var_name, process.env[var_name]</lang>
D
<lang d>import std.stdio, std.process;
void main() {
auto home = getenv("HOME");
}</lang>
<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.
<lang lisp>(lispworks:environment-variable "USER")</lang>
<lang lisp>(sb-ext:posix-getenv "USER")</lang>
<lang lisp>(ccl:getenv "USER")</lang>
<lang lisp>(getenv "HOME")</lang> Ways to do this in some other implementations are listed in the Common Lisp Cookbook.
Delphi /Pascal
<lang Delphi>program EnvironmentVariable;
{$APPTYPE CONSOLE}
uses SysUtils;
begin
WriteLn('Temp = ' + GetEnvironmentVariable('TEMP'));
end.</lang>
E
<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>
Erlang
<lang Erlang> os:getenv( "HOME" ). </lang>
Euphoria
<lang euphoria>puts(1,getenv("PATH"))</lang>
F#
<lang fsharp>open System
[<EntryPoint>] let main args =
printfn "%A" (Environment.GetEnvironmentVariable("PATH")) 0</lang>
Factor
<lang factor>"HOME" os-env print</lang>
Forth
<lang forth>s" HOME" getenv type</lang>
Fortran
<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
Groovy
<lang groovy>System.getenv().each { property, value -> println "$property = $value"}</lang>
Haskell
<lang haskell>import System.Environment main = do getEnv "HOME" >>= print -- get env var
getEnvironment >>= print -- get the entire environment as a list of (key, value) pairs</lang>
HicEst
<lang HicEst>CHARACTER string*255
string = "PATH=" SYSTEM(GEteNV = string)</lang>
Icon and Unicon
<lang Icon>procedure main(arglist)
if *envars = 0 then envars := ["HOME", "TRACE", "BLKSIZE","STRSIZE","COEXPSIZE","MSTKSIZE", "IPATH","LPATH","NOERRBUF"]
every v := !sort(envars) do
write(v," = ",image(getenv(v))|"* not set *")
end</lang>
J
<lang j>2!:5'HOME'</lang>
Java
<lang java>System.getenv("HOME") // get env var System.getenv() // get the entire environment as a Map of keys to values</lang>
JavaScript
The JavaScript language has no facilities to access the computer: it relies on the host environment to provide it.
<lang javascript>var shell = new ActiveXObject("WScript.Shell"); var env = shell.Environment("PROCESS"); WScript.echo('SYSTEMROOT=' + env.item('SYSTEMROOT'));</lang>
Joy
<lang joy>"HOME" getenv.</lang>
Julia
<lang julia>ENV["HOME"]</lang>
K
<lang K>_getenv "HOME"</lang>
Lasso
<lang Lasso>#!/usr/bin/lasso9
define getenv(sysvar::string) => { local(regexp = regexp( -find = `(?m)^` + #sysvar + `=(.*?)$`, -input = sys_environ -> join('\n'), -ignorecase )) return #regexp ->find ? #regexp -> matchString(1) }
stdoutnl(getenv('HOME')) stdoutnl(getenv('PATH')) stdoutnl(getenv('USER')) stdoutnl(getenv('WHAT'))</lang> Output:
/Users/rosetta /opt/local/bin:/opt/local/sbin:/usr/local/bin/:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/opt/X11/bin rosetta
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>
LSL
Rez a box on the ground, and add the following as a New Script. <lang LSL>default { state_entry() { llOwnerSay("llGetTimestamp()="+(string)llGetTimestamp()); llOwnerSay("llGetEnergy()="+(string)llGetEnergy()); llOwnerSay("llGetFreeMemory()="+(string)llGetFreeMemory()); llOwnerSay("llGetMemoryLimit()="+(string)llGetMemoryLimit()); } }</lang> Output:
llGetTimestamp()=2012-07-18T01:26:12.133137Z llGetEnergy()=1.230000 llGetFreeMemory()=16000 llGetMemoryLimit()=65536
Lua
<lang lua>print( os.getenv( "PATH" ) )</lang>
Maple
<lang Maple>getenv("PATH");</lang>
Mathematica
<lang Mathematica>Environment["PATH"]</lang>
MATLAB / Octave
<lang MATLAB> getenv('HOME')
getenv('PATH') getenv('USER')</lang>
Mercury
<lang mercury>:- module env_var.
- - interface.
- - import_module io.
- - pred main(io::di, io::uo) is det.
- - implementation.
- - import_module maybe, string.
main(!IO) :-
io.get_environment_var("HOME", MaybeValue, !IO), ( MaybeValue = yes(Value), io.write_string("HOME is " ++ Value ++ "\n", !IO) ; MaybeValue = no, io.write_string("environment variable HOME not set\n", !IO) ).</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>
NetRexx
When NetRexx runs under a JVM, system ENVIRONMENT variables are complimented by JVM system properties. This sample shows how to get both. <lang NetRexx>/* NetRexx */ options replace format comments java crossref symbols nobinary
runSample(arg) return
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ method sysEnvironment(vn = ) public static
if vn.length > 0 then do envName = vn envValu = System.getenv(envName) if envValu = null then envValu = say envName '=' envValu end else do envVars = System.getenv() key = String loop key over envVars.keySet() envName = key envValu = String envVars.get(key) say envName '=' envValu end key end return
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ method sysProperties(vn = ) public static
if vn.length > 0 then do propName = vn propValu = System.getProperty(propName) if propValu = null then propValu = say propName '=' propValu end else do sysProps = System.getProperties() key = String loop key over sysProps.keySet() propName = key propValu = sysProps.getProperty(key) say propName '=' propValu end key end return
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ method runSample(arg) public static
parse arg ev pv . if ev = then ev = 'CLASSPATH' if pv = then pv = 'java.class.path' say '-'.left(80, '-').overlay(' Environment "'ev'" ', 5) sysEnvironment(ev) say '-'.left(80, '-').overlay(' Properties "'pv'" ', 5) sysProperties(pv) say say '-'.left(80, '-').overlay(' Environment ', 5) sysEnvironment() say '-'.left(80, '-').overlay(' Properties ', 5) sysProperties() say return
</lang> Output:
---- Environment "CLASSPATH" --------------------------------------------------- CLASSPATH = /usr/local/NetRexx/runlib/NetRexxR.jar:. ---- Properties "java.class.path" ---------------------------------------------- java.class.path = /usr/local/NetRexx/runlib/NetRexxR.jar:. ---- Environment --------------------------------------------------------------- HOME = /Users/nrxuser HISTCONTROL = ignoredups USER = nrxuser ZBASHRC = 1 COMMAND_MODE = unix2003 CLASSPATH = /usr/local/NetRexx/runlib/NetRexxR.jar:. SHELL = /bin/bash . . . ---- Properties ---------------------------------------------------------------- java.vm.specification.name = Java Virtual Machine Specification sun.cpu.endian = little sun.io.unicode.encoding = UnicodeBig sun.os.patch.level = unknown file.separator = / java.vendor = Oracle Corporation sun.java.launcher = SUN_STANDARD java.specification.vendor = Oracle Corporation user.home = /Users/nrxuser java.class.path = /usr/local/NetRexx/runlib/NetRexxR.jar:. java.vm.vendor = Oracle Corporation java.runtime.name = Java(TM) SE Runtime Environment . . .
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>getenv("HOME")</lang>
<lang parigp>externstr("echo $HOME")</lang>
In older versions, the command must effectively be triple-quoted: <lang parigp>extern("echo \"\\\"$HOME\\\"\"")</lang> The shell sees <lang bash>echo "\"$HOME\""</lang> which causes it to return
"/home/username"
so that the result is interpreted by GP as a string.
Leaving out the quotation marks allows external commands to return expressions that are then evaluated by GP. For example, <lang parigp>extern("echo Pi")</lang> causes the shell to send Pi back to GP, which interprets the result and returns
%1 = 3.141592653589793238462643383
Perl
The %ENV
hash maps environment variables to their values:
<lang perl>print $ENV{HOME}, "\n";</lang>
Perl 6
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>$Env:Path</lang> To get a complete listing of all environment variables one can simply query the appropriate drive for its contents: <lang powershell>Get-ChildItem Env:</lang>
Prolog
SWI-Prolog has the built in function getenv.
?- getenv('TEMP', Temp).
PureBasic
PureBasic has the built in funtion <lang PureBasic>GetEnvironmentVariable("Name")</lang> Example <lang PureBasic>If OpenConsole()
PrintN("Path:"+#CRLF$ + 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>
Racket
<lang racket>
- lang racket
(getenv "HOME") </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 identifies the pool in which the environmental variables are named. In addition, each operation system (OS) has their own definition as well. This makes it problematic in the accessing/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
- R4
- ROO
for the DOS shell under Microsoft Windows (any version).
(Also successfully tested with Regina under the bash shell in UNIX.)
<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
- Personal REXX
- Regina
- Open Object Rexx
for the DOS shell under Microsoft Windows (any version).
(Also successfully tested with Regina and ooRexx under the bash shell in UNIX.)
<lang rexx>/*REXX program shows how to get an environmental variable under Windows*/
x=value('TEMP',,'ENVIRONMENT')</lang>
The brexx interpreter provides a getenv function for accessing environment variables:
<lang rexx>x=getenv("PATH") /* Get the contents of the path environment variable */</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 environment variable names to their values: <lang ruby>ENV['HOME']</lang>
Run BASIC
<lang runbasic>' ------- Major environment variables ------------------------------------------- 'DefaultDir$ - The folder path where program files are read/written by default 'Platform$ - The operating system on which Run BASIC is being hosted 'UserInfo$ - This is information about the user's web browser 'UrlKeys$ - Contains informational parameters from the URL submitted when the user connected 'UserAddress$ - Contains the IP address of the user 'ProjectsRoot$ - The folder path where Run BASIC keeps programming projects 'ResourcesRoot$ - The folder path where Run BASIC keeps web-servable files 'Err$ - A description of the last runtime error 'Err - A numeric code for the last runtime error (errors that have no code use zero) 'EventKey$ - The id of the object that generated the last user event 'RowIndex - The numeric index of the table or database accessor link that generated the last user event
print "User Info is : ";UserInfo$
print "Platform is : ";Platform$
print "Url Keys is : ";UrlKeys$
print "User Address is: ";UserAddress$
print "Event Key is : ";EventKey$
print "Default Dir is : ";DefaultDir$</lang>
Output: User Info is : Mozilla/5.0 (Windows NT 6.1) AppleWebKit/535.11 (KHTML, like Gecko) Chrome/17.0.963.79 Safari/535.11 Platform is : win32 Url Keys is : none User Address is: 127.0.0.1 Event Key is : none Default Dir is : c:\rbp101
Scala
<lang scala>object Environment_variables extends App {
val variablesToUse = List("PATH", "HOME", "HOMEPATH", "USERNAME") println((for { y <- sys.env x <- variablesToUse if y._1 == x } yield y).sorted.toMap.mkString("\n"))
}</lang>
Seed7
Seed7 provides the function getenv, to get the value of an environment variable. Environment variables are highly operating system dependent. Some variables such as HOME are not always defined and others like PATH use an operating system dependent format (different delimiters). Seed7 provides the functions homeDir and getSearchPath to get the home directory and the search path in an operating system independent manner.
<lang seed7>$ 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>
Smalltalk
Use the OSProcess library to gain access to environment variables:
<lang smalltalk> OSProcess thisOSProcess environment at: #HOME. OSProcess thisOSProcess environment at: #PATH. OSProcess thisOSProcess environment at: #USER. </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
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>$env(HOME)</lang>
TXR
TXR can treat the environment vector as text stream:
<lang txr>@(next :env)
@(collect)
@VAR=@VAL
@(end)</lang>
A recently added gather
directive is useful for extracting multiple items of data from an unordered stream of this kind (not only the environment vector):
<lang txr>@(next :env)
@(gather)
HOME=@home
USER=@user
PATH=@path
@(end)</lang>
What if some of the variables might not exist? Gather has some discipline for that. The following means that three variables are required (the gather construct fails if they are not found), but shell
is optional with a default value of /bin/sh
if it is not extracted from the data:
<lang txr>@(next :env)
@(gather :vars (home user path (shell "/bin/sh")))
HOME=@home
USER=@user
PATH=@path
SHELL=@shell
@(end)</lang>
From TXR Lisp, the environment is available via the (env)
function, which returns a raw list of "name=value
strings. The (env-hash)
function returns a hash from environment keys to their values.
<lang bash>$ ./txr -p "(mapcar (env-hash) '(\"HOME\" \"USER\" \"PATH\"))" ("/home/kaz" "kaz" "/home/kaz/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/home/kaz/bin"</lang>
Here, the hash is being used as a function to filter several environment keys to their values via mapcar
.
Platform note: On POSIX, environment variables, which are extracted using extern char **environ
are assumed to contain UTF-8. On Windows, the GetEnvironmentStringsW
function is used to obtain the environment vector as wide character data.
UNIX Shell
In the Unix Shell Language, environment variables are available as ordinary variables:
<lang bash>echo "$HOME"</lang>
An ordinary variable can be marked as an environment variable with the export
command:
<lang bash>export VAR</lang>
Now child processes launched by the shell will have an environment variable called VAR
.
The Unix command "env" will print out all of the environment variables as key=value pairs on standard output.
Ursala
The argument to the main program is a record initialized by the run-time system in which one of the fields (environs) contains the environment as a list of key:value pairs. <lang Ursala>#import std
- executable ('parameterized',)
showenv = <.file$[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>
XPL0
This task was particularly worthwhile because it revealed a discrepancy in the way 32-bit XPL0 accessed the environment block. A small mod to Tran's PMODE.ASM DPMI was required to make the 32-bit protected-mode version work the same as the 16-bit real-mode versions.
<lang XPL0>include c:\cxpl\codes; \intrinsic 'code' declarations string 0; \use zero-terminated strings int CpuReg, PspSeg, EnvSeg, I, J, C; char EnvVar; [CpuReg:= GetReg; \access CPU registers PspSeg:= CpuReg(9); \get segment address of our PSP EnvSeg:= Peek(PspSeg,$2C) + Peek(PspSeg,$2D)<<8; EnvVar:= "PATH"; \environment variable I:= 0; loop [J:= 0;
loop [C:= Peek(EnvSeg,I); I:= I+1; if C = 0 then quit; if C = EnvVar(J) then [J:= J+1; if J = 4 then [Text(0, EnvVar); \show env. var. loop [C:= Peek(EnvSeg,I); \ and rest of I:= I+1; \ its string if C = 0 then exit; ChOut(0, C); ]; ]; ] else J:= 5; \line must start with environment variable ]; if Peek(EnvSeg,I) = 0 then quit; \double 0 = env. var. not found ];
]</lang>
Output:
PATH=\masm6;C:\;C:\CXPL;C:\UTIL;C:\DOS;C:\BORLANDC\BIN
zkl
<lang zkl>System.getenv("HOME") /home/craigd System.getenv() //--> Dictionary of all env vars</lang>
- Programming Tasks
- Programming environment operations
- Environment variables
- Initialization
- Ada
- ALGOL 68
- AutoHotkey
- AWK
- BASIC
- ZX Spectrum Basic
- Batch File
- BBC BASIC
- C
- C++
- C sharp
- Clojure
- COBOL
- CoffeeScript
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