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

Tunnelblick 3.7.3 - GUI for OpenVPN.
Tunnelblick is a free, open source graphic user interface for OpenVPN on OS X. It provides easy control of OpenVPN client and/or server connections. It comes as a ready-to-use application with all... Read more
Opera 48.0.2685.50 - High-performance We...
Opera is a fast and secure browser trusted by millions of users. With the intuitive interface, Speed Dial and visual bookmarks for organizing favorite sites, news feature with fresh, relevant content... Read more
Tor Browser Bundle 7.0.7 - Anonymize Web...
The Tor Browser Bundle is an easy-to-use portable package of Tor, Vidalia, Torbutton, and a Firefox fork preconfigured to work together out of the box. It contains a modified copy of Firefox that... Read more
FotoMagico 5.5 - Powerful slideshow crea...
FotoMagico lets you create professional slideshows from your photos and music with just a few, simple mouse clicks. It sports a very clean and intuitive yet powerful user interface. High image... Read more
Adobe Audition CC 2018 11.0.0 - Professi...
Audition CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Audition customer). Adobe Audition CC 2018 empowers you to create and... Read more
Alfred 3.5.1 - Quick launcher for apps a...
Alfred is an award-winning productivity application for OS X. Alfred saves you time when you search for files online or on your Mac. Be more productive with hotkeys, keywords, and file actions at... Read more
AirRadar 4.0 - $9.95
With AirRadar, scanning for wireless networks is now easier and more personalized! It allows you to scan for open networks and tag them as favourites or filter them out. View detailed network... Read more
DEVONthink Pro 2.9.16 - Knowledge base,...
Save 10% with our exclusive coupon code: MACUPDATE10 DEVONthink Pro is your essential assistant for today's world, where almost everything is digital. From shopping receipts to important research... Read more
ForkLift 3.0.8 Beta - Powerful file mana...
ForkLift is a powerful file manager and ferociously fast FTP client clothed in a clean and versatile UI that offers the combination of absolute simplicity and raw power expected from a well-executed... Read more
Data Rescue 5.0.1 - Powerful hard drive...
Data Rescue’s new and improved features let you scan, search, and recover your files faster than ever before. We have modernized the file-preview capabilities, added new files types to the recovery... Read more

Wheels of Aurelia (Games)
Wheels of Aurelia 1.0.1 Device: iOS Universal Category: Games Price: $3.99, Version: 1.0.1 (iTunes) Description: | Read more »
Halcyon 6: Starbase Commander guide - ti...
Halcyon 6 is a well-loved indie RPG with stellar tactical combat and some pretty good writing, too. It's now landed on the App Store, so mobile fans, if you're itching for a good intergalactic adventure, here's your game. Being a strategy RPG, the... | Read more »
Game of Thrones: Conquest guide - how to...
Fans of base building games might be excited to know that yet another entry in the genre has materialized - Game of Thrones: Conquest. Yes, you can now join the many kingdoms of the famed book series, or create your own, as you try to conquer... | Read more »
Halcyon 6: Starbase Commander (Games)
Halcyon 6: Starbase Commander 1.4.2.0 Device: iOS Universal Category: Games Price: $6.99, Version: 1.4.2.0 (iTunes) Description: An epic space strategy RPG with base building, deep tactical combat, crew management, alien diplomacy,... | Read more »
Legacy of Discord celebrates its 1 year...
It’s been a thrilling first year for fans of Legacy of Discord, the stunning PvP dungeon-crawling ARPG from YOOZOO Games, and now it’s time to celebrate the game’s first anniversary. The developers are amping up the festivities with some exciting... | Read more »
3 reasons to play Thunder Armada - the n...
The bygone days of the Battleship board game might have past, but naval combat simulators still find an audience on mobile. Thunder Armada is Chinese developer Chyogames latest entry into the genre, drawing inspiration from the explosive exchanges... | Read more »
Experience a full 3D fantasy MMORPG, as...
Those hoping to sink their teeth into a meaty hack and slash RPG that encourages you to fight with others might want to check out EZFun’s new Eternity Guardians. Available to download for iOS and Android, Eternity Guardians is an MMORPG that lets... | Read more »
Warhammer Quest 2 (Games)
Warhammer Quest 2 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Dungeon adventures in the Warhammer World are back! | Read more »
4 of the best Halloween updates for mobi...
Halloween is certainly one of our favorite times for mobile game updates. Many popular titles celebrate this spooky season with fun festivities that can stretch from one week to even the whole month. As we draw closer and closer to Halloween, we'... | Read more »
Fire Rides guide - how to swing to succe...
It's another day, which means another Voodoo game has come to glue our hands to our mobile phones. Yes, it's been an especially prolific month for this particular mobile publisher, but we're certainly not complaining. Fire Rides is yet another... | Read more »

Price Scanner via MacPrices.net

Apple restocks full line of refurbished 13″ M...
Apple has restocked a full line of Apple Certified Refurbished 2017 13″ MacBook Pros for $200-$300 off MSRP. A standard Apple one-year warranty is included with each MacBook, and shipping is free.... Read more
13″ 3.1GHz/256GB MacBook Pro on sale for $167...
Amazon has the 2017 13″ 3.1GHz/256GB Space Gray MacBook Pro on sale today for $121 off MSRP including free shipping: – 13″ 3.1GHz/256GB Space Gray MacBook Pro (MPXV2LL/A): $1678 $121 off MSRP Keep an... Read more
13″ MacBook Pros on sale for up to $120 off M...
B&H Photo has 2017 13″ MacBook Pros in stock today and on sale for up to $120 off MSRP, each including free shipping plus NY & NJ sales tax only: – 13-inch 2.3GHz/128GB Space Gray MacBook... Read more
15″ MacBook Pros on sale for up to $200 off M...
B&H Photo has 15″ MacBook Pros on sale for up to $200 off MSRP. Shipping is free, and B&H charges sales tax in NY & NJ only: – 15″ 2.8GHz MacBook Pro Space Gray (MPTR2LL/A): $2249, $150... Read more
Roundup of Apple Certified Refurbished iMacs,...
Apple has a full line of Certified Refurbished 2017 21″ and 27″ iMacs available starting at $1019 and ranging up to $350 off original MSRP. Apple’s one-year warranty is standard, and shipping is free... Read more
Sale! 27″ 3.8GHz 5K iMac for $2098, save $201...
Amazon has the 27″ 3.8GHz 5K iMac (MNED2LL/A) on sale today for $2098 including free shipping. Their price is $201 off MSRP, and it’s the lowest price available for this model (Apple’s $1949... Read more
Sale! 10″ Apple WiFi iPad Pros for up to $100...
B&H Photo has 10.5″ WiFi iPad Pros in stock today and on sale for $50-$100 off MSRP. Each iPad includes free shipping, and B&H charges sales tax in NY & NJ only: – 10.5″ 64GB iPad Pro: $... Read more
Apple iMacs on sale for up to $130 off MSRP w...
B&H Photo has 21-inch and 27-inch iMacs in stock and on sale for up to $130 off MSRP including free shipping. B&H charges sales tax in NY & NJ only: – 27″ 3.8GHz iMac (MNED2LL/A): $2179 $... Read more
2017 3.5GHz 6-Core Mac Pro on sale for $2799,...
B&H Photo has the 2017 3.5GHz 6-Core Mac Pro (MD878LL/A) on sale today for $2799 including free shipping plus NY & NJ sales tax only . Their price is $200 off MSRP. Read more
12″ 1.2GHz Space Gray MacBook on sale for $11...
Amazon has the 2017 12″ 1.2GHz Space Gray Retina MacBook on sale for $100 off MSRP. Shipping is free: 12″ 1.2GHz Space Gray MacBook: $1199.99 $100 off MSRP Read more

Jobs Board

Product Manager - *Apple* Pay on the *Appl...
Job Summary Apple is looking for a talented product manager to drive the expansion of Apple Pay on the Apple Online Store. This position includes a unique Read more
*Apple* Retail - Multiple Positions - Farmin...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Frameworks Engineer, *Apple* Watch - Apple...
Job Summary Join the team that is shaping the future of software development for Apple Watch! As a software engineer on the Apple Watch Frameworks team you will Read more
*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
Fraud Analyst, *Apple* Advertising Platform...
Job Summary Apple Ad Platforms has an opportunity to redefine advertising on mobile devices. Apple reaches hundreds of millions of iPhone, iPod touch, and iPad Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.