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

Smultron 10.0 - Easy-to-use, powerful te...
Smultron 10 is an elegant and powerful text editor that is easy to use. You can use Smultron 10 to create or edit any text document. Everything from a web page, a note or a script to any single piece... Read more
BetterTouchTool 2.304 - Customize multi-...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom... Read more
Drive Genius 5.0.5 - $49.50 (50% off)
Drive Genius features a comprehensive Malware Scan. Automate your malware protection. Protect your investment from any threat. The Malware Scan is part of the automated DrivePulse utility. DrivePulse... Read more
Apple Keynote 7.3 - Apple's present...
Easily create gorgeous presentations with the all-new Keynote, featuring powerful yet easy-to-use tools and dazzling effects that will make you a very hard act to follow. The Theme Chooser lets you... Read more
Apple Numbers 4.3 - Apple's spreads...
With Apple Numbers, sophisticated spreadsheets are just the start. The whole sheet is your canvas. Just add dramatic interactive charts, tables, and images that paint a revealing picture of your data... Read more
Apple Pages 6.3 - Apple's word proc...
Apple Pages is a powerful word processor that gives you everything you need to create documents that look beautiful. And read beautifully. It lets you work seamlessly between Mac and iOS devices, and... Read more
Smultron 9.4.2 - Easy-to-use, powerful t...
Smultron 9 is an elegant and powerful text editor that is easy to use. Use it to create or edit any text document. Everything from a web page, a note or a script to any single piece of text or code.... Read more
Xcode 9.0 - Integrated development envir...
Xcode includes everything developers need to create great applications for Mac, iPhone, iPad, and Apple Watch. Xcode provides developers a unified workflow for user interface design, coding, testing... Read more
iShowU Instant 1.2.0 - 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
Apple Safari 11.0 - Apple's Web bro...
Note: The direct download link is currently unavailable. It is available in the OS X 10.12.6 release, as well as in the Apple Security Updates. Apple Safari is Apple's web browser that comes with... Read more

The best games to play while you wait fo...
SteamWorld Dig 2 is out this week on PC and Switch, and people are understandably excited. This clever series by Image and Form combines our favorite metroidvania mechanics with an esquisite universe, excellent storytelling, and true wit. While... | Read more »
Drag'n'Boom beginner's gu...
Have you ever wanted to burn and pillage a village as a bloodthirsty dragon? If you answered yes to that question, Drag'n'Boom offers you the perfect chance to do so, casting you as an adorable little dragon that wants to set humankind aflame. It... | Read more »
Thimbleweed Park (Games)
Thimbleweed Park 1.0.0 Device: iOS Universal Category: Games Price: $9.99, Version: 1.0.0 (iTunes) Description: A brand new adventure game from Ron Gilbert and Gary Winnick, creators of the classics Monkey Island and Maniac Mansion!... | Read more »
The best simulation games on mobile
There's nothing like a good sim -- from the seemingly ridiculous to the incredibly mundane, you can be there's a simulation game out there for your every whim. [Read more] | Read more »
INKS guide - how to create works of pinb...
INKS puts a clever new spin on everyone's favorite classic arcade game, pinball. The core mechanics are the same -- keep a little ball pinging around the board for as long as possible without letting it fall into the precarious holes in the board.... | Read more »
Warbands: Bushido (Games)
Warbands: Bushido 1.0 Device: iOS Universal Category: Games Price: $3.99, Version: 1.0 (iTunes) Description: Warbands:Bushido is a miniatures board game with cards, miniatures, dice and beautiful terrains to fight on, with both... | Read more »
The best mobile games like Divinity: Ori...
Divinity: Original Sin 2 launched this week to the excitement of RPG fans everywhere. The game, which derives a lot of of its story and mechanics from old-school isometric RPGs and Dungeons & Dragons, has unseated PlayerUnknown's... | Read more »
Iron Marines guide - beginner tips and t...
Iron Marines is a brilliant RTS title that feels a bit like Starcraft. It's got a sci-fi setting and some of the most spectacular strategy mechanics we've seen in mobile games to date. With that said, the RTS genre can be a bit tricky to break... | Read more »
The best new games we played this week -...
The work week can be tough, but on the bright side, it's almost overandthere are bunches of brand new games to try out this weekend. This week definitely makes up for last week's sleepiness ten-fold. We've got one of the finest RTS game on mobile... | Read more »
Through the Ages (Games)
Through the Ages 1.0.60 Device: iOS Universal Category: Games Price: $9.99, Version: 1.0.60 (iTunes) Description: The offical adaptation of Vlaada Chvátil’s strategy classic, the second best board game ever by Board Game Geek website... | Read more »

Price Scanner via MacPrices.net

Snag a 15-inch 2.2GHz Retina MacBook Pro, App...
Apple has Certified Refurbished 2015 15″ 2.2GHz Retina MacBook Pros available for $1699. That’s $300 off original MSRP, and it’s the lowest price available for a 15″ MacBook Pro currently offered by... Read more
Apple Refurbished 3TB Time Capsule for $279,...
Apple has Certified Refurbished 3TB Time Capsules available for $279 including free shipping plus Apple’s standard one-year warranty. Their price is $120 off MSRP. Read more
19% off Smart Battery Cases for iPhone 7
Amazon has both Black and White Smart Battery Cases for iPhone 7s available for $80.41 including free shipping. Their price is $18.59, or 19%, off MSRP. Read more
Back on sale: 10.5-inch 64GB iPad Pros for $5...
MacMall has 10.5″ 64GB Apple iPad Pros on sale again for $599 including free shipping. That’s $50 off MSRP and the lowest price available for this model from any reseller. Read more
Verizon offers Certified Preowned 16GB iPhone...
Verizon has the 16GB iPhone 6, Certified Preowned, available for $259.99 or $10.83 per month for 24 months. Service plan required. According to Verizon, “All CPO devices have been reconditioned to... Read more
Preorder new iPhone 8 at US Cellular, and tak...
Preorder the new iPhone 8 or iPhone 8 Plus at US Cellular, and take $50 off the prepaid price: – 64GB iPhone 8: $649.99 – 128GB iPhone 8: $799.99 – 64GB iPhone 8 Plus: $749.99 – 128GB iPhone 8 Plus... Read more
12-inch and 9-inch Apple iPad Pros, Certified...
Apple has Certified Refurbished 2016 12″ WiFi iPad Pros available starting at $589. An Apple one-year warranty is included with each model, and shipping is free: – 32GB 12″ iPad Pro WiFi: $589... Read more
QuickerTek Announces Solar PV Chargers for US...
Wichita, Kansas based QuickerTek has announced its new 30 Watt and 60 Watt USB Type-C Solar Juicz Chargers. These solar panels are the only products of their kind, featuring the USB 3.1 adapter cable... Read more
Apple refurbished 128GB iPhone 6s and 6s Plus...
Apple has Certified Refurbished 128GB iPhone 6s and 6s Plus’ available for up to $100 off the price of new models. Space Gray, Silver, Gold, and Rose Gold models are available. Each phone comes... Read more
13-inch 2.3GHz Silver MacBook Pros on sale fo...
B&H Photo has 2017 13″ 2.3GHz Silver MacBook Pros in stock today and on sale for $100 off MSRP, each including free shipping plus NY & NJ sales tax only: – 13-inch 2.3GHz/128GB Silver... Read more

Jobs Board

*Apple* News Product Marketing Mgr., Publish...
Job Summary The Apple News Product Marketing Manager will work closely with a cross-functional group to assist in defining and marketing new features and services. Read more
Development Operations and Site Reliability E...
Development Operations and Site Reliability Engineer, Apple Payment Gateway Job Number: 57572631 Santa Clara Valley, California, United States Posted: Jul. 27, 2017 Read more
*Apple* Solutions Consultant - Apple Inc. (U...
…about helping others on a team while also delighting customers? As an Apple Solutions Consultant (ASC), you will discover customers needs and help connect them Read more
Software/Data Engineer, *Apple* Media Produ...
Job Summary Apple Media Products is the team behind the App Store, Apple Music, iTunes, and many other high profile products on iPhone, Mac and AppleTV. Our Data Read more
SW Engineer , *Apple* Media - Apple Inc. (U...
Job Summary Our team is responsible for exposing Apple Media content and services to the world, and building the infrastructure for next generation internal and Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.