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.

 
AAPL
$105.22
Apple Inc.
+0.39
MSFT
$46.13
Microsoft Corpora
+1.11
GOOG
$539.78
Google Inc.
-4.20

MacTech Search:
Community Search:

Software Updates via MacUpdate

OS X Server 4.0 - For OS X 10.10 Yosemit...
Designed for OS X and iOS devices, OS X Server makes it easy to share files, schedule meetings, synchronize contacts, develop software, host your own website, publish wikis, configure Mac, iPhone,... Read more
TotalFinder 1.6.12 - Adds tabs, hotkeys,...
TotalFinder is a universally acclaimed navigational companion for your Mac. Enhance your Mac's Finder with features so smart and convenient, you won't believe you ever lived without them. Tab-based... Read more
BusyCal 2.6.3 - Powerful calendar app wi...
BusyCal is an award-winning desktop calendar that combines personal productivity features for individuals with powerful calendar sharing capabilities for families and workgroups. BusyCal's unique... Read more
calibre 2.7 - Complete e-library managem...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital... Read more
Skitch 2.7.3 - Take screenshots, annotat...
With Skitch, taking, annotating, and sharing screenshots or images is as fun as it is simple.Communicate and collaborate with images using Skitch and its intuitive, engaging drawing and annotating... Read more
Delicious Library 3.3.2 - Import, browse...
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
Art Text 2.4.8 - Create high quality hea...
Art Text is an OS X application for creating high quality textual graphics, headings, logos, icons, Web site elements, and buttons. Thanks to multi-layer support, creating complex graphics is no... Read more
Live Interior 3D Pro 2.9.6 - Powerful an...
Live Interior 3D Pro is a powerful yet very intuitive interior designing application. View Video Tutorials It has every feature of Live Interior 3D Standard, plus some exclusive ones: Create multi... Read more
The Hit List 1.1.7 - Advanced reminder a...
The Hit List manages the daily chaos of your modern life. It's easy to learn - it's as easy as making lists. And it's powerful enough to let you plan, then forget, then act when the time is right.... Read more
jAlbum Pro 12.2.4 - Organize your digita...
jAlbum Pro has all the features you love in jAlbum, but comes with a commercial license. With jAlbum, you can create gorgeous custom photo galleries for the Web without writing a line of code!... Read more

Latest Forum Discussions

See All

Rami Ismail Opens Up distribute​() for D...
Rami Ismail Opens Up distribute​() for Developers Posted by Jessica Fisher on October 24th, 2014 [ permalink ] Rami Ismail, Chief Executive of Business and Development at indie game studio | Read more »
Great Hitman GO Goes on Sale and Gets Ne...
Great Hitman GO Goes on Sale and Gets New Update – Say That Three Times Fast Posted by Jessica Fisher on October 24th, 2014 [ permalink ] | Read more »
Rival Stars Basketball Review
Rival Stars Basketball Review By Jennifer Allen on October 24th, 2014 Our Rating: :: RESTRICTIVE BUT FUNUniversal App - Designed for iPhone and iPad Rival Stars Basketball is a fun mixture of basketball and card collecting but its... | Read more »
Rubicon Development Makes Over a Dozen o...
Rubicon Development Makes Over a Dozen of Their Games Free For This Weekend Only Posted by Jessica Fisher on October 24th, 2014 [ permalink ] | Read more »
I Am Dolphin Review
I Am Dolphin Review By Jennifer Allen on October 24th, 2014 Our Rating: :: NEARLY FIN-TASTICUniversal App - Designed for iPhone and iPad Swim around and eat nearly everything that moves in I Am Dolphin, a fun Ecco-ish kind of game... | Read more »
nPlayer looks to be the ultimate choice...
Developed by Newin Inc, nPlayer may seem like your standard video player – but is aiming to be the best in its field by providing high quality video play performance and support for a huge number of video formats and codecs. User reviews include... | Read more »
Fighting Fantasy: Caverns of the Snow Wi...
Fighting Fantasy: Caverns of the Snow Witch Review By Jennifer Allen on October 24th, 2014 Our Rating: :: CLASSY STORYTELLINGUniversal App - Designed for iPhone and iPad Fighting Fantasy: Caverns of the Snow Witch is a sterling... | Read more »
A Few Days Left (Games)
A Few Days Left 1.01 Device: iOS Universal Category: Games Price: $3.99, Version: 1.01 (iTunes) Description: Screenshots are in compliance to App Store's 4+ age rating! Please see App Preview for real game play! **Important: Make... | Read more »
Toca Boo (Education)
Toca Boo 1.0.2 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0.2 (iTunes) Description: BOO! Did I scare you!? My name is Bonnie and my family loves to spook! Do you want to scare them back? Follow me and I'll... | Read more »
Intuon (Games)
Intuon 1.1 Device: iOS Universal Category: Games Price: $.99, Version: 1.1 (iTunes) Description: Join the battle with your intuition in a new hardcore game Intuon! How well do you trust your intuition? Can you find a needle in a... | Read more »

Price Scanner via MacPrices.net

Weekend sale: 13-inch 128GB MacBook Air for $...
Best Buy has the 2014 13-inch 1.4GHz 128GB MacBook Air on sale for $849.99, or $150 off MSRP, on their online store. Choose free home shipping or free local store pickup (if available). Price valid... Read more
Nimbus Note Cross=Platform Notes Utility
Nimbus Note will make sure you never forget or lose your valuable data again. Create and edit notes, save web pages, screenshots and any other type of data – and share it all with your friends and... Read more
NewerTech’s Snuglet Makes MagSafe 2 Power Con...
NewerTech has introduced the Snuglet, a precision-manufactured ring designed to sit inside your MagSafe 2 connector port, providing a more snug fit to prevent your power cable from unintentional... Read more
Apple Planning To Sacrifice Gross Margins To...
Digitimes Research’s Jim Hsiao says its analysts believe Apple is planning to sacrifice its gross margins to save its tablet business, which has recently fallen into decline. They project that Apple’... Read more
Who’s On Now? – First Instant-Connect Search...
It’s nighttime and your car has broken down on the side of the highway. You need a tow truck right away, so you open an app on your iPhone, search for the closest tow truck and send an instant... Read more
13-inch 2.5GHz MacBook Pro on sale for $949,...
Best Buy has the 13″ 2.5GHz MacBook Pro available for $949.99 on their online store. Choose free shipping or free instant local store pickup (if available). Their price is $150 off MSRP. Price is... Read more
Save up to $125 on Retina MacBook Pros
B&H Photo has the new 2014 13″ and 15″ Retina MacBook Pros on sale for up to $125 off MSRP. Shipping is free, and B&H charges NY sales tax only. They’ll also include free copies of Parallels... Read more
Apple refurbished Time Capsules available sta...
The Apple Store has certified refurbished Time Capsules available for up to $60 off MSRP. Apple’s one-year warranty is included with each Time Capsule, and shipping is free: - 2TB Time Capsule: $255... Read more
Textilus New Word, Notes and PDF Processor fo...
Textilus is new word-crunching, notes, and PDF processor designed exclusively for the iPad. I haven’t had time to thoroughly check it out yet, but it looks great and early reviews are positive.... Read more
WD My Passport Pro Bus-Powered Thunderbolt RA...
WD’s My Passport Pro RAID solution is powered by an integrated Thunderbolt cable for true portability and speeds as high as 233 MB/s. HighlightsOverviewSpecifications Transfer, Back Up And Edit In... Read more

Jobs Board

*Apple* Solutions Consultant - Apple Inc. (U...
…important role that the ASC serves is that of providing an excellent Apple Customer Experience. Responsibilities include: * Promoting Apple products and solutions Read more
Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Project Manager / Business Analyst, WW *Appl...
…a senior project manager / business analyst to work within our Worldwide Apple Fulfillment Operations and the Business Process Re-engineering team. This role will work Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.