TweetFollow Us on Twitter

Environment Variables What they are and how to use them

Volume Number: 23 (2007)
Issue Number: 07
Column Tag: MacEnterprise

Environment Variables

What they are and how to use them

By Philip Rinehart, Yale University

HISTORY

As with any Unix operating system, Macintosh OS X recognizes the use of environment variables. For a quick refresher, environment variables are traditionally used in shell scripts to retrieve information about the operating environment. Common environment variables are used each time a new Terminal session is launched, including PATH, HOME, and other less common variables. OS X extends this concept with application bundles and Launch Services. Let's begin by examining the traditional use of environment variables by OS X and their associated scope.

The Terminal

The single most common invocation of environment variables is when the Terminal application is launched. Each time a new shell is opened by the Terminal application, a new session is created with system wide environment variables. Let's look at the two environment variables that are created for each session in a standard Tiger installation.

PATH

The PATH environment variable is probably the single most common variable that is changed in any terminal session. In a standard OS X installation, the file /etc/profile is used to set the PATH variable. It is also used for any remote session when connected to any remote machine with ssh. By default, the variable is set at PATH="/bin:/sbin:

/usr/bin:/usr/sbin". Why might one change this default value? What if useful binaries live in other directories?

As an example, a standard fink or macports installation installs binaries either in /sw or /opt/local/bin. In this case, the modification of profile to reflect the directory is important. For Macports, open profile in an editor and add /opt/local/bin to the PATH. Any session created with the Terminal application or via ssh will now search the PATH including /opt/local/bin. Any binary that has been installed in /opt/local/bin is now available to a Terminal session or a remote ssh session.

One quick note: be careful when setting the PATH system wide, as the PATH is searched beginning with the first directory listed. When installing macports, or fink for that matter, if the directory is listed first, the binaries installed by these collections are used first. This might be problematic if the system binary is what is desired when calling any program.

PS1

PS1 is created for each new Terminal window through use a second file in /etc, bashrc. This file creates the custom command prompt, showing hostname, current working directory, and username. This file can also be altered, as profile can, so that any user logging into the system has an identical command prompt. Note though, the bashrc file is only read when using the bash shell (the default shell in OS X 10.4), not when using other shells such as tcsh, or zsh.

One last bit about OS X, and the use of the Terminal application. Environment variables can be set in any Terminal window. It is important to note that any newly set environment variables are not inherited if a new shell session is invoked, and cannot, therefore, be depended on. For this reason, it is best practice, at least, to edit profile to apply environment variables for each user on the host operating system.

Graphical User Interface applications

OS X has the unique ability to use a plist stored in ~/.MacOSX/environment.plist to access any environment variable. The plist is registered by loginwindow, so that non-Terminal based applications could use environment variables for their operation. However, one environment variable, DYLD_LIBRARY_PATH, was noted as a security risk in Security Update 2007-004. As noted on the MacEnterprise list, the change in behavior affected some applications, most notably the IBM Workplace Forms Viewer, used for governmental grant applications. If the environment.plist method is subject to change, is there a more reliable method to access environment variables? Yes, application specific environment variables!

Application-specific environment variables

Prior to launching any application, environment variables can be set in the info.plist file within an application bundle. Launch Services then reads the environment variable, and uses it for dynamic configuration of the application. This method is exactly what was used from a suggestion by Josh Wisenbaker, and implemented by Ben Hanes. Let's look at how it works.

By default, an application created in XCode includes a bare bones Info.plist file. The file contains basic information about the application bundle. It commonly contains information about the application, copyright, icon file information as well as other application specific information. It really is up to the developer to specify information as listed in the Apple Runtime Configuration Guidelines. For the purpose of this article, the particular key of interest is LSEnvironment. It is a dictionary value, and contains a complete list of environment variables that are read prior to launch of the application bundle. Launch Services reads the variables, and uses them when the application is launched. It is important to note, this use of environment variable only works when the application is launched from the Finder. Let's return to the example application that created problems to see how this works in practice.

The first step is opening the application bundle. Most bundles are similar to Figure 1 below.


Figure 1.

The file that needs to be edited for any application bundle to register an environment variable is Info.plist. Opening the IBM Workplace Forms Viewer Info.plist, add the environment variables required by this application. Here is the relevant dictionary that is added:

   <key>LSEnvironment</key>
   <dict>
      <key>DYLD_LIBRARY_PATH</key>
      <string>/Applications/IBM Workplace Forms/IBM Workplace Forms Viewer.app/Contents/¬
      MacOS:/Applications/IBM Workplace Forms/IBM Workplace Forms Viewer.app/Contents/¬
      MacOS/API/70/system</string>
      <key>PUREEDGE_INI</key>
      <string>/Applications/IBM Workplace Forms/IBM Workplace Forms Viewer.app/Contents/MacOS/PureEdgeAPI.ini</string>
   </dict>

Take a close look, the key is specified in this example as documented by Apple's Developer documentation, LSEnvironment. Two separate environmental variables are then set, DYLD_LIBRARY_PATH, and PUREEDGE_INI. Other applications can use this exact method, including SyBase SQL Anywhere 9 and USAnimation's Harmony.

Armed with the knowledge of how to set environment variables, both for the terminal and for Finder based applications, it should be trivial to correct applications which do not function as expected if environment variables are not set. Until next month, see you on the lists!


Philip Rinehart is co-chair of the steering committee leading the Mac OS X Enterprise Project (macenterprise.org) and is the Lead Mac Analyst at Yale University. He has been using Macintosh Computers since the days of the Macintosh SE, and Mac OS X since its Developer Preview Release. Before coming to Yale, he worked as a Unix system administrator for a dot-com company. He can be reached at: philip.rinehart@yale.edu.

The MacEnterprise project is a community of IT professionals sharing information and solutions to support Macs in an enterprise. We collaborate on the deployment, management, and integration of Mac OS X client and server computers into multi-platform computing environments.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Navicat Premium Essentials 15.0.11 - Pro...
Navicat Premium Essentials is a compact version of Navicat which provides basic and necessary features you will need to perform simple administration on a database. It supports the latest features... Read more
Delicious Library 3.9 - Import, browse a...
Delicious Library allows you to import, browse, and share all your books, movies, music, and video games with Delicious Library. Run your very own library from your home or office using our... Read more
ffWorks 2.0.1 - Convert multimedia files...
ffWorks, focused on simplicity, brings a fresh approach to the use of FFmpeg, allowing you to create ultra-high-quality movies without the need to write a single line of code on the command-line.... Read more
TeamViewer 15.3.2682 - Establish remote...
TeamViewer gives you remote control of any computer or Mac over the Internet within seconds or can be used for online meetings. Find out why more than 200 million users trust TeamViewer! Free for non... Read more
Affinity Designer 1.8.1 - Vector graphic...
Affinity Designer is an incredibly accurate vector illustrator that feels fast and at home in the hands of creative professionals. It intuitively combines rock solid and crisp vector art with... Read more
Wireshark 3.2.2 - Network protocol analy...
Wireshark is one of the world's foremost network protocol analyzers, and is the standard in many parts of the industry. It is the continuation of a project that started in 1998. Hundreds of... Read more
Affinity Photo 1.8.1 - Digital editing f...
Affinity Photo - redefines the boundaries for professional photo editing software for the Mac. With a meticulous focus on workflow it offers sophisticated tools for enhancing, editing and retouching... Read more
iShowU Instant 1.3.2 - Full-featured scr...
iShowU Instant gives you real-time screen recording like you've never seen before! It is the fastest, most feature-filled real-time screen capture tool from shinywhitebox yet. All of the features you... Read more
NeoFinder 7.5.1 - Catalog your external...
NeoFinder (formerly CDFinder) rapidly organizes your data, either on external or internal disks, or any other volumes. It catalogs and manages all your data, so you stay in control of your data... Read more
App Tamer 2.5 - Efficiently manage your...
App Tamer tames your processor-monopolizing apps and keeps them from chewing up excessive CPU time and battery life. Powered by a unique AutoStop feature, App Tamer stops each application when you... Read more

Latest Forum Discussions

See All

Amon Amarth Berserker is a side-scrollin...
Amon Amarth Berserker is the latest game from Ride & Crash and serves as a follow up to the previous title that was simply called Amon Amarth. It's available now as a premium title for both iOS and Android. [Read more] | Read more »
Team up with your guildmates to take on...
MU Origin 2's latest update is now live and brings with it two new Abyss-related events to challenge Guilds. There are also a few new features that will allow players to enhance their costumes, an increased level cap and more. [Read more] | Read more »
Build Your Own Apple Arcade, For $400
Apple Arcade has been out for a little over a month, and I’m not entirely thrilled with it. It’s definitely an interesting idea, but it leaves a lot to be desired, especially in fulfilling its commitment to letting folks “play anywhere.” Still, at... | Read more »
Creepy Little Monsters is a cute, monste...
Creepy Little Monsters is a retro throwback that sees you traversing tricky puzzle-platformer levels as a one-eyed monster. It aims to offer a fresh take on 80s and 90s classics of the genre, and it's out right now for iOS and Android. [Read more... | Read more »
Tyrant's Arena delivers intense her...
Tyrant's Arena is an intense midcore multiplayer actioner where you'll compete in tricky 3v3 matches to crush your opponents and earn neat rewards. It comes to us from developer Kroy Games, and it's now available for pre-registration on iOS and... | Read more »
Mobile Games Starter Kit
Over here at 148Apps, we regularly dive deep into the latest and greatest mobile games hitting the App Store, but that’s not always what people are looking for when searching for a new mobile game. Some folks just want to dip their toes into... | Read more »
Unresolved is a hard-hitting narrative a...
Ghofran Akil's Unresolved in an upcoming text-based adventure game that sees you playing as a mother attempting to find her disappeared husband during the Lebanese Civil War. [Read more] | Read more »
Marvel Strike Force introduces new brawl...
FoxNext's squad-based RPG Marvel Strike Force is set to receive some fresh characters from the X-Men and Iron Man series. They'll arrive as part of the game's latest update, which follows a sizable spending boycott on the title due to complaints... | Read more »
Speed Dating for Ghosts is a narrative a...
Speed Dating for Ghosts originally released on Steam back 2018, since then it has received honourable mentions for narrative during the Independent Games Festival. Now it's made its way over to iOS devices where it's available as a premium title... | Read more »
Fast-paced multiplayer title Tennis Star...
Tennis Stars: Ultimate Clash is the latest free-to-play tennis title to hit iOS and Android. It's said to be a fairly casual experience, offering easy-to-learn controls and fast-paced, mobile-friendly matches. [Read more] | Read more »

Price Scanner via MacPrices.net

Back in stock! Apple’s 4-core and 6-core 2018...
Apple has Certified Refurbished 2018 Mac minis available on their online store for $120-$170 off the cost of new models. Each mini comes with a new outer case plus a standard Apple one-year warranty... Read more
10″ 128GB iPads on sale today at Amazon for $...
Amazon has new 10.2″ 128GB WiFI iPads for $100 off Apple’s MSRP. These are the same iPads sold by Apple in their retail and online stores. Note that some sale prices may be restricted to certain... Read more
Orcam MyEye 2 Is Inspiration Apple Needs To M...
EDITORIAL: 02.28.20- It’s no secret that Apple is planning to further expand into the wearables segment, working quietly behind the scenes to create its own smart glasses — as rumors have suggested... Read more
Boost Mobile 1-day Flash Sale: $100 off all A...
Boost Mobile is offering Apple’s 2019 iPhone 11 and 11 Pro models for $100 off MSRP. Boost is also offering the same $100 discount on new previous-generation iPhone XS, XR, X, 8, and 7 models. For... Read more
13″ 1.4GHz Silver MacBook Pros on sale for $1...
B&H Photo has new 2019 13″ 1.4GHz Silver MacBook Pros on sale for $150 off Apple’s MSRP today with prices starting at $1149. Overnight shipping is free to many addresses in the US. These are the... Read more
Apple resellers offer $150-$170 discounts on...
Amazon has new 2019 13″ MacBook Airs on sale for $150-$170 off Apple’s MSRP, with prices starting at $949, each including free shipping. These are the same MacBook Airs Apple sells in their retail... Read more
B&H is again offering $100 discounts on M...
B&H Photo has 4-Core and 6-Core Mac minis on sale for $100 off Apple’s standard MSRP, with prices starting at only $699. Overnight shipping is free to many US addresses: – 3.6GHz Quad-Core mini... Read more
B&H Photo drops iMac prices, offers model...
B&H Photo has new 2019 21″ and 27″ 5K iMacs in stock today and on sale for up to $250 off Apple’s MSRP, with prices starting at only $999. These are the same iMacs sold by Apple in their retail... Read more
Flash sale! 11″ 64GB WiFi iPad Pro for $674,...
Walmart has the 11″ 64GB WiFi iPad Pro on sale on their online store today for $674. That’s $125 off Apple’s MSRP for this model and the cheapest price available from any Apple reseller. Choose free... Read more
Sale! Get the 256GB 13″ Silver MacBook Air fo...
Amazon has new 2019 13″ 1.6GHz/256GB MacBook Airs, in Silver, on sale today for only $999 shipped. Their price is $300 off Apple’s MSRP for this model, and it’s the cheapest price for a 256GB MacBook... Read more

Jobs Board

Windows/ *Apple* Technical Support Engineer...
Windows/ Apple Technical Support Engineer Key Role: Serve as a part of a dynamic corporate technical support group. Provide Tier III technical support and monthly Read more
Medical Assistant - *Apple* Valley Clinic -...
…professional, quality care to patients in the ambulatory setting at the M Health Fairview Apple Valley Clinic, located in Apple Valley, MN. Join the **M Health Read more
Medical Assistant - *Apple* Valley Clinic -...
…professional, quality care to patients in the ambulatory setting at the M Health Fairview Apple Valley Clinic, located in Apple Valley, MN. Join the **M Health Read more
Geek Squad Advanced Repair *Apple* Professi...
**764652BR** **Job Title:** Geek Squad Advanced Repair Apple Professional **Job Category:** Store Associates **Store NUmber or Department:** 000245- Apple Read more
Medical Assistant - *Apple* Valley Clinic -...
…professional, quality care to patients in the ambulatory setting at the M Health Fairview Apple Valley Clinic, located in Apple Valley, MN. Join the **M Health Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.